RIKEN Lunch Seminar Talks and Other Information
July 2018  

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JUL
27
Friday
Nuclear Theory/RIKEN Seminar
"Jets as a probe of transverse spin physics"
Presented by Zhongbo Kang, UCLA
2 pm, Building 510, CFNS Seminar Room 238
Friday, July 27, 2018, 2:00 pm
Hosted by: Chun Shen
Jets are collimated spray of hadrons that are naturally produced in high energy colliders. They are powerful probes of many different aspects of QCD dynamics. In this talk, we will demonstrate how to use jets to explore the transverse momentum dependent (TMD) physics. A novel TMD framework to deal with backtoback two particle correlations is presented, with which we could study the Sivers asymmetry for photon+jet or dijet production in transversely polarized protonproton collisions. At the end of the talk, we also show how jet substructure could be used to explore the TMD fragmentation functions. We expect these studies to have important applications at RHIC in the future.
Nuclear Theory/RIKEN Seminar
"Confronting hydrodynamic predictions with XeXe heavyion collision data"
Presented by Matt Luzum, Univeristy of Sao Paulo
Friday, July 13, 2018, 2 pm
Building 510, CFNS Seminar Room 238
Hosted by: Chun Shen
Comparing collision systems of different size, at near the same collision energy, offers us the opportunity to probe the scaling behavior and therefore the nature of the system itself. Recently, we made predictions for XeXe collisions at 5.44 TeV using viscous hydrodynamic simulations, noting that the scaling from the larger PbPb system is rather generic, and arguing that robust predictions can be made that do not depend on details of the model. Here we confront our predictions with measurements that were subsequently made in a short XeXe run at the LHC by the ALICE, ATLAS, and CMS collaborations. We find that the predictions are largely confirmed, with small discrepancies that could point the way to a better understanding of the medium created in such collisions.
RIKEN Lunch Seminar
"Topological structures in finite temperature QCD"
Presented by Rasmus Larsen, BNL
Thursday, July 12, 2018, 12:30 pm
Building 510, Room 2160
Hosted by: Yuya Tanizaki
We report our study on the properties of the topological structures present in the QCD medium. We use dynamical domain wall fermion configurations on lattices of size 32^3x8 and detect the topological structures through the zero modes of the overlap operator. We explicitly show that the properties of the zero modes of the QCD Dirac operator agrees well with that of calorons with nontrivial holonomy. Different profiles of the zero modes are observed, ranging from solutions that are localized in all four spacetime dimensions, to profiles that are localized in the spatial directions, and constant along the temporal extent of the lattice. This indicates towards the presence of instantondyons in the hot QCD medium around Tc, where the distance between dyons control the shape and extent of the zero modes.
Nuclear Theory/RIKEN Seminar
"Liouville action, high multiplicity tail and shape of proton"
Presented by Vladimir Skokov, BNL
Friday, June 1, 2018, 2 pm
CFNS Seminar Room, 238
Hosted by: Chun Shen
In this talk I violate the common wisdom "one seminar — one message" and discuss two seemingly unrelated results in the framework of the dilutedense CGC approach: the effect of spatial eccentricity of the projectile (proton) shape on the second harmonic in doubleinclusive gluon production and the theoretical description of the high gluon multiplicity tail. I will show that these two superficially unrelated results in combination may lead to unexpected consequences for the phenomenology of pA collisions.
Joint Nuclear Theory/RIKEN/CFNS Seminar
"Novel QCD Physics at an ElectronIon Collider"
Presented by Stanley Brodsky, SLAC National Accelerator Laboratory, Stanford University
Friday, May 25, 2018, 10:30 am
Building 510, CFNS Seminar Room 238
Hosted by: Chun Shen
An electronion collider can test many fundamental features of QCD for hadron and nuclear physics, including flavordependent antishadowing in deep inelastic electronnucleus scattering, the breakdown of sum rules for nuclear structure functions, the role of ``hiddencolor " degrees of freedom, and the effects of "color transparency" on the baryontomeson anomaly observed at high transverse momentum in heavyion collisions. I will also discuss intrinsic heavy quark phenomena and the production of exotic multiquark states at the EIC. On the theory side, I will discuss the new insights into color confinement that one obtains from lightfront holography, including supersymmetric features of the meson, baryon, and tetraquark spectroscopy. The Principle of Maximum Conformality (PMC) can be used to systematically eliminate renormalization scale ambiguities and thus obtain schemeindependent pQCD predictions.
HET/RIKEN Lunch Seminar
"Quantum Simulation from Quantum Chemistry to Quantum Chromodynamics"
Presented by Peter Love, Tufts
Thursday, May 10, 2018, 12:30 pm
Building 510, Room 2160
Hosted by: Mattia Bruno and Enrico Rinaldi
Quantum simulation proposes to use future quantum computers to calculate properties of quantum systems. In the context of chemistry, the target is the electronic structure problem: determination of the electronic energy given the nuclear coordinates of a molecule. Since 2006 we have been studying quantum approaches to quantum chemical problems, and such approaches must face the challenges of high, but fixed, precision requirements, and fermion antisymmetry. I will describe several algorithmic developments in this area including improvements upon the Jordan Wigner transformation, alternatives to phase estimation, adiabatic quantum computing approaches to the electronic structure problem, methods based on sparse Hamiltonian simulation techniques and the potential for experiments realizing these algorithms in the near future. I will also briefly review work by others on the analog and digital simulation of lattice gauge theories using quantum simulators.
Nuclear Theory/RIKEN Seminar
"Exploring the QCD phase structure with functional methods"
Presented by BerndJochen Schaefer, University of Giessen
Friday, April 27, 2018, 2 pm
Building 510, CFNS Seminar Room 238
Hosted by: Chun Shen
QCD at finite temperature and moderate densities predicts a phase transition from a chiral symmetry broken hadronic phase to a chirally restored deconfined quarkgluon plasma phase. In this talk I report on recent progress achieved basically with functional renormalization group (FRG) methods to reveal the QCD phase structure. Two and three quark flavor FRG investigations are confronted to results obtained with effective chiral lowenergy models. The importance of quantum and thermal fluctuations is demonstrated and their consequences for the experimental signatures to detect possible critical endpoints in the phase diagram are discussed.
Nuclear Theory/RIKEN Seminar
"Dense nuclear and quark matter from holography"
Presented by Andreas Schmitt, University of Southampton
Friday, April 6, 2018, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Chun Shen
QCD at large, but not asymptotically large, baryon density presents an enormous theoretical challenge because firstprinciple calculations are nearly impossible. Phenomenologically, dense QCD is of great interest for the interior of neutron stars, in particular after the recent detection of gravitational waves from neutron star mergers. I will discuss a holographic approach to dense matter, making use of the SakaiSugimoto model, which can account for both nuclear matter and quark matter and the transition between them. In particular, nucleons are implemented as instantons in the bulk, and I will discuss certain approximations for manynucleon matter based on the flatspace instanton solution and present the resulting phase diagrams.
Nuclear Theory/RIKEN Seminar
"Correlators of twist2 lightray operators in the BFKL approximation"
Presented by Ian Balitsky
Friday, March 16, 2018, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Andrey Tarasov
It is well known that BFKL gives anomalous dimensions of twist2 operators of spin j in the "BFKL limit'' $g^2\righarrow 0,\omega\equiv j1\righarrow 0,{g^2\over\omega}$ fixed. I demonstrate that such limit describes the nonlocal lightray operators and present the results of calculation of two and threepoint correlation functions of these operators in this limit. The calculation is performed in ${\cal N}$=4 SYM but the result is valid in other gauge theories such as QCD.
Nuclear Theory/RIKEN Seminar
"YangMills action on the light front: MHV amplitudes and Wilson lines"
Presented by Anna Stasto, Penn State
Friday, March 9, 2018, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Chun Shen
The MHV action is the YangMills action quantized on the lightfront, where the two explicit physical gluonic degrees of freedom have been canonically transformed to a new set of fields. This transformation leads to the action with vertices being offshell continuations of the MHV amplitudes. We show that the solution to the field transformation expressing one of the new fields in terms of the YangMills field is a certain type of the Wilson line. More precisely, it is a straight infinite gauge link with a slope extending to the lightcone minus and the transverse direction. One of the consequences of that fact is that certain MHV vertices reduced partially onshell are gauge invariant — a fact discovered before using conventional lightfront perturbation theory. We also analyze the diagrammatic content of the field transformations leading to the MHV action. We found that the diagrams for the solution to the transformation (given by the Wilson line) and its inverse differ only by lightfront energy denominators.
Nuclear Theory/RIKEN Seminar
"Quark / Antiquark Correlations in HeavyLight Ion Collisions"
Presented by Matt Sievert, LANL
Friday, March 2, 2018, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Chun Shen
It has long been known that subnucleonic fluctuations of the energy density in the initial stages of heavy ion collisions play an important role in generating the observed distributions of particles and their flow. These energy density fluctuations are dominated by the radiation of smallx gluons which are populated to classically large occupation numbers in the wave functions of ultrarelativistic heavy ions. While these soft gluons dominate the initial conditions for the energy density, it is quark production which determines the initial conditions of other conserved charges, like flavor and baryon number. With the recent development of stateofthe art hydrodynamics codes tailored to the Beam Energy Scan which can propagate these conserved charges into the final state, it is timely and important to calculate the initial conditions of these conserved charges from first principles in QCD. In this talk, I will present new results for the spatial correlations among quarks and antiquarks produced at midrapidity by pair production from smallx gluons. This singlepair production mechanism, which has been studied for some time in momentum space, is the leading contribution to these correlations in coordinate space for dilutedense collisions. As one moves from the dilutedense regime toward the densedense regime, correlations due to double pair production become more important, and these correlations persist over larger length scales than the singlepair production mechanism. Over nonperturbative length scales, only the correlations from the overlap geometry remain. I will present explicit results for quarkantiquark correlations due to single pair production, and I will outline some preliminary results for the various doublepair production mechanisms. The ultimate goal of this work will be to construct a code which can initialize these conserved charges over all length scales in heavyion collisions.
HighEnergy Physics & RIKEN Theory Seminar
"Preparing High Energy Physics Software for the Future  the Community White Paper"
Presented by Dr. Benedikt Hegner, CERN, Switzerland
Wednesday, February 28, 2018, 12 pm
Seminar Room, Bldg. 725
Hosted by: Eric Lancon
Particle physics has an ambitious and broad experimental program for the coming decades. This program requires large investments in detector hardware, either to build new facilities and experiments, or to upgrade existing ones. Similarly, it requires commensurate investment into R&D of software to acquire, manage, process, and analyses the shear amounts of data to be recorded. In planning for the High Luminosity LHC in particular, it is critical that all of the collaborating stakeholders agree on the software goals and priorities, and that their efforts complement each other. In this spirit, the High Energy Physics community has created a white paper (arXiv:1712.06982) to describe and define the R&D activities required in order to prepare for this software upgrade. This presentation describes the expected software and computing challenges, and the plans to address them that are laid out in the white paper.
Nuclear Theory/RIKEN Seminar
"New nonperturbative scales and glueballs in confining gauge theories"
Presented by Mohamed Anber, Lewis & Clark College
Friday, February 2, 2018, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Chun Shen
Studying confining gauge theories on a circle can provide answers to some of the deepest questions about QCD. In this talk, I start by summarizing the main characteristics shared by the compactified theories and their four dimensional cousins. Next, I show that the glueball spectrum of the compactified theories is much richer than what have been thought before. In particular, new nonperturbative scales and glueballs emerge in the deep IR regime of the theory. I discuss the spectrum in the context of super YangMills and show that the lightest glueball states fill a chiral supermultiplet with doubly nonperturbative binding energy. I end with possible implications of these findings for the four dimensional gauge theories.
RIKEN Lunch Seminar
"Exact results on massless 3flavor QCD through new anomaly matching"
Presented by Yuya Tanizaki, RBRC
Thursday, January 25, 2018, 12:30 pm
Building 510, Room 2160
Hosted by: Enrico Rinaldi
Recently, we find a new 't Hooft anomaly of massless 3flavor QCD, and it turns out to be useful for constraining the possible chiral symmetry breaking at finite density and zero temperature. We briefly review the anomaly matching by a toy example, and show that massless 3flavor QCD has an 't Hooft anomaly related to ''center'' and discrete axial symmetries. We also discuss its consequences on the expectation value of the special symmetrytwisting operator, which gives the phase diagram of socalled Z(3)QCD.
Nuclear Theory/RIKEN Seminar
"Semiinclusive jet cross sections within SCET"
Presented by Felix Ringer, LBL
Friday, January 19, 2018, 2 pm
Small Seminar Room, Bldg. 510
We review the denition of semiinclusive jet functions within Soft Collinear Eective Theory (SCET) and their application to inclusive jet cross sections. We consider the fully inclusive production cross section of jets as well as several jet substructure observables in protonproton collisions relevant for the LHC and RHIC. The corresponding semiinclusive jet functions satisfy renormalization group (RG) equations which take the form of standard timelike DGLAP evolution equations, analogous to collinear fragmentation functions. By solving these RG equations, the resummation of potentially large single logarithms n s lnn R can be achieved. We present numerical results at NLO+NLLR accuracy and compare to the available data.
RIKEN Lunch Seminar
"Worldline Approach to Chiral Kinetic Theory and the Chiral Magnetic Effect"
Presented by Niklas Mueller, BNL
Thursday, January 18, 2018, 12:30 pm
Building 510, Room 1224
Hosted by: Enrico Rinaldi
Experimental searches for messengers of CP and P odd phenomena at RHIC and LHC have attracted much interest and are a prime motivation for significant theoretical effort: Anomalous and topological effects receive important contributions from the preequilibrium phase of a collision and an interesting question of phenomenological relevance is how the chiral imbalance generated at early times persists through a fluctuating background of sphalerons in addition to other "nonanomalous" interactions with the QGP. To address this question, we construct a relativistic chiral kinetic theory using the worldline formulation of quantum field theory. We outline how Berry's phase arises in this framework, and how its effects can be clearly distinguished from those arising from the chiral anomaly. We further outline how this framework can be matched to classical statistical simulations at early times and to anomalous chiral hydrodynamics at late times.
RIKEN Lunch Seminar
"Threedimensional gauge theories using lattice regularization"
Presented by Nikhil Karthik
Thursday, January 11, 2018, 12:30 pm
Building 510, Room 2160
Hosted by: Yuya Tanizaki
Threedimensional gauge theories with massless fermions provide a simple yet nonperturbative setting to understand why QCD has a scale, and also provide effective descriptions of condensed matter systems. Along these lines, I will present results on infrared scaling and scalebreaking in threedimensional QED, QCD and largeNc theories. I will also present some preliminary results on threedimensional QED with one flavor of fermion regulated with and without parity anomaly.
Nuclear Theory/RIKEN Seminar
"Thermodynamics of string bits"
Presented by Sourav Raha, University of Florida
Friday, January 5, 2018, 2 pm
Small Seminar Room, Bldg. 510
We study the Hagedorn transition in the singlet sector of the simplest superstring bit model in the tensionless limit. The gauge group of our model is SU(N) and this transition takes place when N is infinite. We use orthogonality of group characters in order to calculate the partition function. At the Hagedorn temperature there is a change in the distribution of parameters that maximize this partition function. We conclude by devising a fieldtheoretic interpretation of the this phenomenon.
Nuclear Theory/RIKEN Seminar
"Simultaneous extraction of spindependent parton distributions"
Presented by Nobuo Sato, Jlab/University of Connecticut
Friday, December 15, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Andrey Tarasov
In this talk, I will present a recent global QCD analysis of spindependent PDFs and FFs using a MC methodology by the Jefferson Angular Momentum collaboration (JAM).
RIKEN Lunch Seminar
"Pushing the boundaries of relativistic fluid dynamics"
Presented by Jorge Noronha
Thursday, December 7, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Enrico Rinaldi
For nearly a century, dissipative effects have been included in fluid dynamics using gradients of macroscopic quantities such as the temperature and fluid velocity. Recently, results from heavy ion collision experiments and explicit model calculations have pushed the boundaries of relativistic fluid dynamics towards the farfromequilibrium regime. In this talk I will present calculations of the large order behavior of the gradient expansion, both in kinetic theory and in holography, which have demonstrated that this series has zero radius of convergence. I will discuss the role played by novel nonequilibrium attractor solutions in determining the emergence of fluid dynamic behavior in manybody systems under extreme conditions.
Nuclear Theory/RIKEN seminar
"Medium modification of jet and jetinduced medium excitation"
Presented by Shanshan Cao, Wayne State University
Friday, December 1, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Chun Shen
A coupled linear Boltzmann transport and hydrodynamics model (CoLBThydro) is developed for concurrent simulation of jet propagation and hydrodynamic evolution in highenergy nuclear collisions. Diverse microscopic scattering processes (elastic and inelastic) are incorporated for parton showers, and both massive and massless partons are calculated on the same footing. Energy deposition from jets into nuclear matter is treated as source term of hydrodynamic evolution. Within this CoLBThydro model, nuclear modification of heavy and light flavor hadrons are simultaneously described. Evidence of jetinduced medium excitation is explored with photontriggered jets, where significant enhancement of soft hadron production is found due to energy deposition from jets.
Nuclear Theory/RIKEN Seminar
"Higherorder corrections to jet quenching"
Presented by Yacine MehtarTani, University of Washington
Friday, November 17, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Chun Shen
The phenomenon of jet quenching in ultrarelativistic heavy ion collisions reveals to effect of substantial finial state interactions which cause QCD jets to lose energy to the quarkgluon plasma (QGP), mainly by induced gluon radiation. In standard analytic approaches to energy loss, jets are approximated by single partons and thus higherorder effects in the strong coupling constant are neglected. This may prove insufficient to reliably extract QGP properties at high pT, where a significant jet suppression was recently reported by the ATLAS collaboration in PbPb collisions at the LHC. In this work we explore higherorder corrections to the inclusive jet spectrum which may be sizable owing to the fact that the probability for a highly virtual parton to split in the medium increases with the jet pT. As the effective number of jet constituents increases, jets are expected to lose more energy than a single color charge. This translates into large logarithmic enhancements of higherorders in the perturbative series, that need to be resummed. As a result we obtain a Sudakovlike suppression factor which we investigate in the leading logarithmic approximation. We note, however, that the phase space for higherorder corrections is mitigated by coherence effects that relate to the fact that, below a characteristic angular scale, the medium does not resolve the inner jet structure. In this case, the jet lose energy coherently as a single color charge, namely, the primary parton.
RIKEN Lunch Seminar
"QCD from gluon, quark, and meson correlators"
Presented by Mario Mitter, BNL
Thursday, November 16, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Hiromichi Nishimura
We present nonperturbative firstprinciple results for quark, gluon and meson 1PI correlation functions of twoflavour Landaugauge QCD in the vacuum and YangMills theory at finite temperature. They are obtained by solving their Functional Renormalisation Group equations in a systematic vertex expansion, aiming at apparent convergence within a selfconsistent approximation scheme. These correlation functions carry the full information about the theory and their connection to physical observables is discussed. The presented calculations represent a crucial prerequisite for quantitative firstprinciple studies of QCD and its phase diagram within this framework. In particular, we have computed the ghost, quark and scalarpseudoscalar meson propagators, as well as gluon, ghostgluon, quarkgluon, quark, quarkmeson, and meson interactions and the magnetic and electric components of the gluon propagator, and the three and fourgluon vertices. Our results stress the crucial importance of the quantitatively correct running of different vertices in the semiperturbative regime for describing the phenomena and scales of confinement and spontaneous chiral symmetry breaking without phenomenological input. We confront our results for the correlators with lattice simulations and compare our Debye mass to hard thermal loop perturbation theory. Finally, applications to "QCDenhanced" lowenergy effective models of QCD are discussed.
RIKEN Lunch Seminar
"Approach to equilibrium of quarkonium in quarkgluon plasma"
Presented by Xiaojun Yao, BNL
Thursday, October 26, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Hiromichi Nishimura
Quarkonium can be used as a probe of quarkgluon plasma (QGP) in heavy ion collisions. The production process is complicated by several factors: plasma screening effect, inmedium dissociation and recombination, cold nuclear matter effect and feeddown contributions. In this talk, I will present a set of Boltzmann transport equations that govern the inmedium evolution of the heavy quark and quarkonium system. The dissociation and recombination rates are calculated from potential nonrelativistic QCD at leading order. I will explain how the system reaches equilibrium in a QGP box and show how the system evolves under a boost invariant longitudinal expansion. I will argue that the angular distribution of quarkonium probes the stages at which recombination occurs. The presented framework will be extended in future work to include other factors influencing quarkonium production.
Nuclear Theory/RIKEN Seminar
"Quantization of threebody scattering amplitude in isobar formulation"
Presented by Maxim Mai, George Washington University
Friday, October 20, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Chun Shen
In the socalled isobar parametrization the threeparticle states are populated via an interacting twoparticle system (resonant or nonresonant), and a spectator. Using this parametrization, we derive the isobarspectator interaction such that the threebody Unitarity is ensured exactly. In the first part of my talk I will show the major steps of this derivation. (arXiv:1706.06118) The second part of the talk will be dedicated to the finitevolume implementation of the framework (arXiv:1709.08222). Imaginary parts in the infinite volume, dictated by Unitarity, determine the dominant powerlaw finite volume effects to ensure the correct 3body quantization condition. Furthermore, various building blocks of the 3>3 amplitude in the finite volume can become singular. However, when all contributions are summedup, only genuine 3body singularities remain. I will demonstrate the corresponding cancellation mechanisms explicitly for the simplified case of only one Swave isobar.
RIKEN Lunch Seminar
"Lattice QCD and Neutrino Physics"
Presented by Aaron Meyer, HET Group
Thursday, October 19, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Enrico Rinaldi
The nucleon axial form factor is a dominant contribution to systematic uncertainties in neutrino oscillation studies. The most commonly used model parametrization of the axial form factor has uncontrolled and underestimated systematic errors. Firstprinciples computations from lattice QCD have the potential to control theory errors by disentangling the effects of nuclear corrections from the nucleon amplitudes. In this talk, I discuss fits to the axial form factor with deuterium bubble chamber data using the modelindependent $z$ expansion parameterization. I then present preliminary results for a blinded lattice QCD calculation of the nucleon axial charge $g_A$ with physical light quark masses. This calculation is being done with the Highly Improved Staggered Quark (HISQ) action and 2+1+1 flavors of sea quarks.
Nuclear Theory/RIKEN Seminar
"What can we learn from flow observables in heavyion collisions?"
Presented by Jacquelyn NoronhaHostler, Rutgers University
Thursday, October 12, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Chun Shen
The Quark Gluon Plasma (QGP), nature's first and most perfect liquid, has been successfully reproduced in heavyion collisions at RHIC and the LHC. The dynamics of the QGP can be well described by relativistic viscous hydrodynamics, allowing for precise comparisons to experimental data in order to extract the properties of the QGP. While a small shear viscosity is wellestablished, questions still remain regarding the precise initial state, the temperature dependence of viscosity, the smallest system that displays QGPlike properties, and the equation of state at large densities. In this talk, the various flow harmonic observables are analyzed to help answer these remaining questions.
Nuclear Theory/RIKEN Seminar
"QCD on a small circle"
Presented by Aleksey Cherman, University of Washington
Friday, September 29, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
Recent developments have shown that QCDlike theories can be engineered to remain in a confined phase when compactified on an arbitrarily small circle, where their features may be studied quantitatively in a controlled fashion. I'll explain how a nonperturbative mass gap and chiral symmetry breaking, which are both historically viewed as prototypical strong coupling effects, appear from systematic weakcoupling calculations. Then I'll describe the rich spectrum of hadronic states, including glueball, meson, and baryon resonances in the calculable smallcircle context.
RIKEN Lunch Seminar
"Color Memory, Large Gauge Transformations, and Soft Theorems in YangMills Theory"
Presented by Monica Pate, Harvard University
Thursday, September 28, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Hiromichi Nishimura
An infinite dimensional symmetry group which governs the infrared sectors of gauge and gravity theories has been recently discovered. This symmetry can be established both from an asymptotic symmetry analysis as well as from the corresponding Ward identities which are quantum field theoretic soft theorems. Moreover, the spontaneous breaking of these symmetries induces vacuum transitions which are detectable by charged particles through the socalled memory effect. In this seminar, I will explain the precise equivalence between asymptotic symmetries, soft theorems and memory effects in the context of tree level YangMills. In particular, in this context the soft gluon theorem is Ward identity of a large gauge symmetry, whose action on the vacuum can be measured from the relative color charge of colored detectors.
Nuclear Theory/RIKEN Seminar
"TMD gluon distributions for dijet production and their behavior at small x"
Presented by Elena Petreska, NIKHEF
Friday, September 15, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
Starting from the Color Glass Condensate (CGC) cross section for dijet production in protonnucleus collisions we derive a transversemomentumdependent (TMD) factorization formula for small transversemomentum imbalance of the jets and for finite number of colors. For the eight TMD distributions appearing in the cross section we determine their operator definitions at smallx as CGC correlators of Wilson lines and we study their JIMWLK evolution. We find that at large transverse momentum the universality of TMDs gets restored. We also discuss an extension of the approach to generalized TMDs (GTMDs) that can give an insight into the angular correlations between impact parameter and dipole size in the CGC framework.
RIKEN Lunch Seminar
"Thermal Fluctuations in Hydrodynamic Simulations of QGP"
Presented by Mayank Singh, McGill University
Thursday, September 14, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Hiromichi Nishimura
Multiparticle correlations measured in heavyion collision experiments carry info on fluctuations present in the entire evolutionary history of the system. Initial states include geometric and quantum fluctuations and are important contributors. The thermal fluctuations during the course of QGP evolution is another conceptually important source of these fluctuations and should be studied in detail. We begin by treating thermal fluctuations as a linearized perturbation on hydrodynamic background. We present a full calculation of hadronic and photonic observables including these fluctuations. Recently we have included fluctuations in our simulations in a nonperturbative manner. Progress based on this approach will be discussed.
Nuclear Theory/RIKEN Seminar
"QCD corrections to highpT hadron production in ep scattering"
Presented by Werner Vogelsang, Tuebingen University
Friday, August 25, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
We discuss various cross sections and spin observables in highpT hadron production in lepton proton collisions, with special focus on the role of perturbative QCD corrections. We present phenomenological studies relevant for present fixedtarget experiments and for a future EIC.
Nuclear Theory/RIKEN Seminar
"Factorization and phenomenology for Transverse Momentum Dependent distributions"
Presented by Ignazio Scimemi, Universidad Complutense de Madrid
Friday, August 18, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
Factorization and phenomenology for Transverse Momentum Dependent distributions Abstract: The factorization of the hadronic part of the cross sections plays a central role in our comprehension of collider physics. I will review some aspects of the factorization, like the appearence of rapidity divergences and the related subtractions and log resummation (up to higher orders in QCD perturbative expansion) in transverse momentum dependent cross sections. As an application I will describe the inclusion of the TMD formalism in an analysis of vector boson production data.
RIKEN Lunch Seminar
"Revisit the energy density and the gluon spectrum in the boostinvariant Glasma from a semianalytic approach"
Presented by Ming Li
Thursday, August 17, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Hiromichi Nishimura
In high energy heavyion collisions, the soft degrees of freedom at the very initial stage after the collision can be effectively represented by strong classical gluonic fields within the Color Glass Condensate framework. Understanding the spacetime evolution of the system is equivalent to solving the classical YangMills equations for the gluonic fields. There have been many efforts in the past two decades in numerically solving these equations. In this talk, on the contrary, I will use a semianalytic approach that assumes the solution has the form of a power series expansion in the proper time. I will discuss the energymomentum tensor and the gluon spectrum obtained from this approach and make comparisons with the numerical results in the literature.
Nuclear Theory/RIKEN Seminar
"Resummation of nonglobal logarithms in QCD"
Presented by Yoshitaka Hatta, Kyoto University
Friday, August 11, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
The large angle emission of soft gluons from QCD jets gives rise to the socalled nonglobal logarithms. In this talk I discuss the resummation of nonglobal logarithms at finite Nc with particular emphasis on its deep connection to the smallx logarithms in high energy scattering.
Nuclear Theory/RIKEN Seminar
"General formulae for dipole Wilson line correlators with the Color Glass Condensate"
Presented by Kenji Fukushima, University of Tokyo
Friday, August 4, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
I talk about general formulae to compute Wilson line correlators with the Color Glass Condensate approximated by the McLerranVenugopalan model. Specifically, as an application, I explain about a perturbative expansion of the dipole correlators in terms of 1/N_c to derive fully analytical expressions. I finally discuss the validity of the largeN_c expansion by calculating the higherorder harmonics of the flow observables in the dipole model.
Nuclear Theory/RIKEN Seminar
"Holographic Pomeron: Scattering, saturation, entropy and black hole."
Presented by Ismail Zahed, Stony Brook
Friday, July 7, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
I will discuss the general nature of the holographic Pomeron as a quantum QCD string exchange in both flat and curved AdS space for both pp and ep collisions at either large energies or small x. This description leads naturally to the concept of weestrings and their distribution both in rapidity and transverse space. The holographic Pomeron carries intrinsic temperature and entropy, with the latter being identical to the recently reported entanglement entropy. I will show that this nonperturbative description of the Pomeron cross over to the the perturbative one, with a phase boundary dominated by string balls, i.e. long and massive strings near their intrinsic Hagedorn temperature. These string balls lead to a distribution of large multiplicity pp events that is in agreement with the one reported for pp collisions at the LHC. I will show that at lowx, the quantum string is so entangled that very weak string selfinteractions can cause it to turn to a black hole. I will suggest that lowx saturation occurs when the density of weestrings reaches the Bekenstein bound, with a proton size that freezes with increasing rapidity.
Nuclear Theory/RIKEN Seminar
"Probing Transverse Momentum Broadening in Heavy Ion Collisions"
Presented by Feng Yuan, LBL
Friday, June 30, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
In this talk, we will discuss the dijet azimuthal decorrelation in relativistic heavy ion collisions as an important probe of the transverse momentum broadening effects in heavy ion collisions. We take into account both the soft gluon radiation in vacuum associated with the Sudakov logarithms and the jet PTbroadening effects in the QCD medium. We find that the Sudakov effects are dominant at the LHC, while the medium effects can play an important role at RHIC energies. This explains why the LHC experiments have not yet observed sizable PTbroadening effects in the measurement of dijet azimuthal correlations in heavy ion collisions. Future investigations at RHIC will provide a unique opportunity to study the PTbroadening effects and help to pin down the underlying mechanism for jet energy loss in a hot and dense medium.
Nuclear Theory/RIKEN Seminar
"Better fitting through (fictitious) chemistry"
Presented by Pasi Huovinen, Uniwersytet Wroclawski
Monday, June 19, 2017, 10 am
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
One of the puzzles we have faced at the LHC is why the thermal models apparently cannot properly fit the yield of protons. I will explore how the fit improves if we assume that nucleonantinucleon annihilations freezeout way later than all other number changing processes or if strange particles freezeout before nonstrange particles, and how this affects the final particle distributions in hydrodynamical calculations.
Nuclear Theory/RIKEN Seminar
"Exploring the phase structure and dynamics of QCD"
Presented by Jan Pawlowski, Heidelberg
Friday, June 16, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
The past years have seen tremendous progress in the description of Quantum Chromodynamics at vanishing and finite temperature and density with functional approaches, such as the functional renormalisation group or DysonSchwinger equations. Within these approaches QCD correlation functions of quarks, gluon and hadrons are computed nonperturbatively from first principles. In the talk I will discuss results for the phase structure of QCD at finite temperature and density, as well as for thermodynamical obserables such as the pressure and the trace anomaly. The approach is also applied to baryon number fluctuations. By now functional approaches also allow for a direct computation of transport coefficients in QCD. First results concern the temperature dependence of the shear viscosity over entropy ratio in YangMills theory and QCD. The talk concludes with a discussion of the further prospects for our understanding of the phase structure and dynamics of QCD.
Nuclear Theory/RIKEN Seminar
"Gluon structure of hadrons and nuclei"
Presented by Phiala Shanahan, MIT
Friday, June 9, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
I will present the results of recent lattice QCD studies of the gluon generalised form factors of both hadrons and light nuclei. The generalised transversity gluon distributions are of particular interest since they are purely gluonic; they do not mix with quark distributions at leading twist. In light nuclei they moreover provide a clean signature of nonnucleonic degrees of freedom. The goal of these studies is to provide QCD predictions to be tested at an electronion collider (EIC) designed to access gluon structure quantities including transversemomentum dependent distributions (TMDs) and gluon generalised parton distributions (GPDs).
Nuclear Theory/RIKEN Seminar
"Hydrodynamic Fluctuations in Heavy Ion Collisions"
Presented by Derek Teaney, Stony Brook
Friday, June 2, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
We develop a set of kinetic equations for hydrodynamic fluctuations which are equivalent to nonlinear hydrodynamics with noise. The hydrokinetic equations can be coupled to existing secondorder hydrodynamic codes to incorporate the physics of these fluctuations. We use the hydrokinetic equations to analyze thermal fluctuations for a Bjorken expansion, evaluating the contribution of thermal noise from the earliest moments and at late times. In the Bjorken case, the solution to the kinetic equations determines the coefficient of the first fractional power of the gradient expansion $ \sim 1/(\tau T)^{3/2}$ for the expanding system. Numerically, we find that the contribution to the longitudinal pressure from hydrodynamic fluctuations is larger than secondorder hydrodynamics for typical medium parameters used to simulate heavy ion collisions. Subsequently we analyze the behaviour of hydrodynamic fluctuations of near the QCD critical point, and dilineate the relevance KiblleZurek scaling relative to other physics. If time permits we will also describe how thermal fluctuations place a lower bound on the bulk viscosity of QCD. References: Y.~Akamatsu, A.~Mazeliauskas and D.~Teaney, ``A kinetic regime of hydrodynamic fluctuations and long time tails for a Bjorken expansion,'' [arXiv:1606.07742 [nuclth]]. Y.~Akamatsu, D. Teaney, F. Yan, Y. Yin, ``Transitting the critical point,'' in progress.
RIKEN Lunch Seminar
"Mixed Anomaly and Global Consistency"
Presented by Yuya Tanizaki, RBRC
Thursday, May 25, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Hiromichi Nishimura
Symmetry and topology are powerful tools to study strongly interacting dynamics. In this talk, we will see that mixed 't Hooft anomaly and global consistency strongly constrains the possible lowenergy dynamics in a simple quantum mechanical example. I will briefly explain the same idea is useful to study the phase diagram of bifundamental gauge theories at finite theta angles.
Nuclear Theory/RIKEN Seminar
"Probing nucleon substructure with Bayesian parameter estimation"
Presented by Scott Moreland, Duke
Friday, May 5, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
Multiparticle correlations observed in small collision systems at top LHC energies exhibit signatures which are similar to those observed in large collision systems and generally attributed to the formation of a deconfined quarkgluon plasma (QGP). This suggests that even protonproton and protonlead collisions may produce small droplets of QGP which translate spatial inhomogeneities into finalstate momentum anisotropies. A primary challenge in testing hydrodynamic descriptions of small collision systems is in modeling the initial stages of the collision. In this talk, I discuss recent efforts to apply Bayesian methodology to parametric descriptions of initial state physics. I show that such methods can be extended to smaller length scales which include partonic degrees of freedom and glean information regarding the fluctuating nature of the proton.
RIKEN Lunch Seminar
"Lattice study of gauge theory with multiple fermion representations"
Presented by Ethan Neil, University of Colorado, Boulder and RBRC
Thursday, May 4, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Enrico Rinaldi
"There is longstanding theoretical interest in the behavior of a stronglycoupled gauge theory in the presence of multiple fermions charged under different representations of the gauge group. In addition to the question of whether generation of dynamically separated scales will occur, such theories appear commonly in UV realizations of composite Higgs models with partially composite top quarks. I will present a first lattice study of SU(4) gauge theory with fermions in each of the two lowestlying representations, discussing the finitetemperature phase structure and lowlying spectrum. Connections to BSM physics through a particular composite Higgs model will also be made."
Nuclear Theory/RIKEN Seminar
"Analyticity in Spin and Causality in Conformal Theories"
Presented by Simon CaronHuot, McGill
Friday, April 28, 2017, 2 pm
Large Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
The conformal bootstrap aims to calculate scaling dimensions and correlation functions in various theories, starting from general principles such as unitarity and crossing symmetry. I will explain that local operators are not independent of each other but organize into analytic functions of spin, and I will present a formula, extending a classic one due to Froissart and Gribov in the early days of Regge theory, which quantifies the consequences of this fact. Applications will include a new way to solve crossing symmetry at large spin, as well as new bounds encoding bulk locality in theories with a gravity dual. Based on 1703.00278.
Nuclear Theory/RIKEN Seminar
"Forward particle production in pA: implementing the NLO hybrid formalism"
Presented by Tuomas Lappi, University of Jyväskylä
Friday, April 21, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
Single inclusive particle production cross sections in high energy hadron collisions at forward rapidity are an important benchmark process for the CGC picture of small x QCD. The process can be calculated in the "hybrid formalism", where a collinear largex quark or gluon scatters off the dense color field of the target. Recent calculations at nexttoleading order in perturbation theory have not led to a stable physical result for the single inclusive cross section at high transverse momenta. The problem with these NLO calculations lies in the subtraction procedure for the soft "rapidity" divergence which must be absorbed into BK renormalization group evolution of the target. This talk discusses recent work to understand and resolve the problems with the subtraction procedure. In particular, we have recently implemented numerically the quark channel production cross section using a new rapidity factorization procedure proposed by Iancu et al. For a fixed coupling one does indeed obtain a physically meaningful cross section which is positive and reduces in a controlled way to previous leading order calculations. However, it is not yet clear how to generalize this to running coupling in a way that is fully consistent with previous leading order calculations in coordinate space.
Nuclear Theory/RIKEN Seminar
"Effect of magnetic field on flow fluctuations in"
Presented by Ajit M. Srivvastava
Friday, April 14, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
Very strong magnetic fields can arise in noncentral heavyion collisions at ultrarelativistic energies, which may not decay quickly in a conducting plasma. We carry out magnetohydrodynamics simulations to study the effects of this magnetic field on the evolution of the plasma and on resulting flow fluctuations. Our results show that magnetic field leads to enhancement in elliptic flow, while flow fluctuations lead to reorganization of magnetic flux resulting in a transient increase in the local magnetic field. We also show generation of vorticity arising from nontrivial dependence of magnetosonic waves on pressure gradients and magnetic field direction. Magnetic field from collision of deformed nuclei shows very nontrivial features and can lead to qualitatively new effects on plasma evolutions. We discuss possibility of dynamo effect in the presence of vortices if any exotic high baryon density QCD phases are achieved in heavyion collisions.
Nuclear Theory/RIKEN Seminar
"Anisotropic dissipative fluid dynamics  foundations & applications in heavyion physics"
Presented by Professor Dirk Rischke, Johann Wolfgang GoetheUniversität
Friday, April 7, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
In collisions of heavy ions at ultrarelativistic energies, a system of hot and dense strongly interacting matter is created. This matter exhibits a surprisingly strong degree of collectivity, implying a short mean free path of its constituents and, consequently, a small shear viscositytoentropy density ratio. This allows to describe the evolution of the system using relativistic dissipative fluid dynamics. Dissipative fluid dynamics can be understood as an expansion around local thermodynamical equilibrium, corresponding to the idealfluid limit where dissipative corrections are absent. A short mean free path means that this expansion is well defined and converges sufficiently rapidly. Nevertheless, in the initial stage of a heavyion collision, spacetime gradients of the fluiddynamical fields (energymomentum and netcharge densities) are so large that dissipative corrections to the idealfluid limit can become sizable. In this situation, novel approaches to relativistic dissipative fluid dynamics are called for. One such approach is anisotropic dissipative fluid dynamics, which is based on an expansion around an anisotropic nonequilibrium state (instead of local thermodynamical equilibrium, as in conventional dissipative fluid dynamics). In this talk, I present a derivation of the equations of motion of anisotropic dissipative fluid dynamics from the Boltzmann equation, using the method of moments. I also discuss how to resolve an ambiguity to close the system of equations of motion in the case when there are no corrections to the anisotropic state which constitutes the basis of the moment expansion.
A Special HET/RIKEN Lunch Seminar
"The Road to Nuclear Physics from Standard Model"
Presented by Zohreh Davoudi, MIT
Thursday, April 6, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Hiromichi Nishimura
At the core of nuclear physics is to understand complex phenomena occurring in the hottest and densest known environments in nature, and to unravel the mystery of the dark sector and other new physics possibilities. Nuclear physicists are expected to predict, with certainty, the reaction rates relevant to star evolutions and nuclear energy research, and to obtain the "standard" effects in nuclei to reveal information about the "nonstandard" sector. To achieve such certainty, the field has gradually started to eliminate its reliance on the phenomenological models and has entered an era where the underlying interactions are "effectively" based on the Standard Model of particle physics, in particular Quantum Chromodynamics (QCD). The fewnucleon systems can now emerge directly from the constituent quark and gluon degrees of freedom and with only QCD interactions in play, using the numerical method of lattice QCD. Fewbody observable, such as fewnucleon interactions and scattering amplitudes, as well transition amplitudes and reaction rates, have been the focus of this vastly growing field, as once obtained from QCD, and matched to effective field theories, can advance and improve the nuclear manybody calculations of exceedingly complex systems. This talk is a brief introduction to this program and its goals, with a great focus on the progress in fewbody observables from QCD.
RIKEN Lunch Seminar
"The hadronic lightbylight contribution to muon g2 from lattice QCD"
Presented by Luchang Jin, BNL
Thursday, March 30, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Enrico Rinaldi
The current measurement of muonic g2 disagrees with the theoretical calculation by about 3 standard deviations. Hadronic vacuum polarization (HVP) and hadronic light by light (HLbL) are the two types of processes that contribute most to the theoretical uncertainty. The current value for HLbL is still given by models. We report our latest lattice calculation of hadronic lightbylight contribution to muon g2 using our recent developed moment method. The connected diagrams and the leading disconnected diagrams are included. The calculation is performed on a 48^3 × 96 lattice with physical pion mass and 5.5 fm box size. We expect sizable finite volume and finite lattice spacing corrections to the results of these calculations which will be estimated in calculations to be carried out over the next 12 years.
Nuclear Theory/RIKEN Seminar
"A solitonic approach to neutron stars: The (BPS) Skyrme model"
Presented by Carlos Naya, Durham
Friday, March 24, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
The Skyrme model is a low energy effective field theory of strong interactions where nuclei and baryons appear as collective excitations of pionic degrees of freedom. Proposed by Tony Skyrme in the sixties, his ideas received further support when it was discovered that in the limit of the large number of colours of QCD, an effective theory of mesons arises. In the last years, there has been a revival of Skyrme's ideas and new related models, some of them with BPS bounds (topological lower energy bounds), have been proposed. It is the aim of this talk to focus on the one known as BPS Skyrme model. After a brief introduction to this BPS limit we study its application to neutron stars where we will find that high maximal masses are supported. In addition, the BPS Skyrme model allow us to perform both meanfield and exact calculations and a comparison between both approaches will be presented.
Nuclear Theory/RIKEN Seminar
"Universal Transverse Momentum Dependent Fragmentation"
Presented by Duff Neill, LANL
Friday, March 17, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
Fragmentation is the earliest and perhaps most interesting QCD jet observable, since it directly deals with the partonhadron duality at the end of the QCD cascade. The most basic fragmentation observables all enjoy the property of being universal, in the sense that a sufficiently energetic parton that initiates the cascade factorizes from the rest of the event, so that the underlying soft structure of the event to a good approximation does not change the fragmentation spectrum. With the luminosities and resolution of modern detectors, we can begin to study the fragmentation process in three dimensions: both the energy spectrum and the transverse fluctuations to the collinear direction of initiating hard parton. However, when one wants to study the transverse fluctuations, one becomes very sensitive to the underlying jet definition, in particular, how the collinear direction is defined. Intuitive definitions of the jet direction, like the total momentum of the jet constituents, are inherently sensitive to soft processes, and can spoil the universality of the spectrum. I will discuss how a simple change in the jet definition removes this soft sensitivity, and allows one to study the intrinsic three dimensional structure of collinear splittings, which should be process independent.
RIKEN Lunch Seminar
"FiniteTemperature Perturbative QCD confronts Lattice"
Presented by Thorben Graf, University of Frankfurt
Thursday, March 9, 2017, 12:30 pm
Building 510, Room 1224
Hosted by: Heikki Mantysaari
Since decades expressions for the thermodynamic potential were calculated perturbatively at finite temperature (and density) and pushed to higher orders. I review the current status of these efforts including resummation techniques and compare them to results of lattice Monte Carlo simulations and address unanswered questions. Finally, I present results for several thermodynamic quantities within the nexttoleading order calculation of the thermodynamic potential at finite T and \mu including nonvanishing quark masses.
RIKEN Lunch Seminar
"Generalized NambuGoldstone theorem"
Presented by Yoshimasa Hidaka, RIKEN
Thursday, March 2, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Hiromichi Nishimura
Symmetry and its spontaneous breaking are of basic importance for understanding the low energy physics in manybody systems. When a continuum symmetry is spontaneously broken, there exist a zero mode called NambuGoldstone (NG) mode, which is well developed in Lorentz invariant systems. In contrast, in nonLorentz invariant systems, the NG theorem has not been well developed. In this talk, we discuss the recent progress in generalization of NG theorem in nonrelativistic systems, open systems, and systems with higher form symmetries.
RIKEN Lunch Seminar
"The KibbleZurek scaling for the Entanglement Entropy on the scalar field in 1+1 dimension"
Presented by Akio Tomiya, CCNU
Monday, February 27, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Hiromichi Nishimura
The entanglement entropy is a candidate of an entropy in Nonequilibrium physics and recently, relaxation or thermalization is studied through the entanglement entropy with quamtum quenching, which is sudden change of parameter(s) in the Hamiltonian of the system. Global quantum quench with a finite rate which crosses critical points is known to lead to universal scaling of correlation functions as functions of the quench rate. We explore scaling properties of the entanglement entropy of a subsystem of a scaler field on the lattice, harmonic chain, during a mass quench which asymptotes to finite constant values at early and late times and for which the dynamics is exactly solvable. Both for fast and slow quenches we find that the entanglement entropy has a constant term plus a term proportional to the subsystem size. For slow quenches, the constant piece is consistent with Kibble Zurek predictions. Furthermore, the quench rate dependence of the extensive piece enters solely through the instantaneous correlation length at the KibbleZurek time, suggesting a new scaling hypothesis similar to that for correlation functions. This talk is based on arXiv:1702.04359.
RIKEN Lunch Seminar
"Pathintegral formula for local thermal equilibrium"
Presented by Masaru Hongo, RIKEN
Thursday, February 23, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Hiromichi Nishimura
Relativistic hydrodynamics is formulated based on the assumption that systems are almost in local thermal equilibrium. However, a quantum field theoretical way to handle such a locally thermalized system has not been clearly clarified. In this study, we develop a complete pathintegral formulation of relativistic quantum fields in local thermal equilibrium, which brings about the emergence of thermally induced curved spacetime. The obtained pathintegral formula for local thermal equilibrium enables us to derive nondissipative part of hydrodynamic constitutive relations based on symmetry arguments. As one application, we discuss a field theoretical derivation of anomalous hydrodynamics which captures the chiral magnetic/vortical effects.
RIKEN Lunch Seminar
"The search for gluon saturation in pA collisions and at the EIC"
Presented by Bowen Xiao, Central China Normal University
Thursday, February 16, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Heikki Mantysaari
In this talk, I plan to discuss the recent theoretical progress towards the exploration of the gluon saturation phenomenon in pA collisions and at the future EIC. Two important pillars of this exploration are the single inclusive forward hadron productions and forward dijet correlations, which have both been computed up to oneloop order within the smallx factorization formalism. Complementary measurements in pA collisions and at the EIC can help us measure smallx gluon distributions and test the generalized smallx factorization. In addition, DIS diffractive dijet process is another interesting process which is sensitive to the dipole Wigner gluon distributions. This process can provide us 3D tomographic images of lowx gluons inside high energy protons and nuclei.
Nuclear Theory/RIKEN Seminar
"What shines brighter, Glasma or QuarkGluon Plasma?"
Presented by Naoto Tanji, University of Heidelberg
Friday, January 27, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
Recent classicalstatistical numerical simulations have established the "bottomup" thermalization scenario of Baier et al. as the correct weak coupling effective theory for thermalization in ultrarelativistic heavyion collisions. I will talk on a parametric study of photon production in the various stages of this bottomup framework to ascertain the relative contribution of the offequilibrium "Glasma" relative to that of a thermalized QuarkGluon Plasma. Taking into account the constraints imposed by the measured charged hadron multiplicities at RHIC and the LHC, we find that Glasma contributions are important especially for large values of the saturation scale at both energies. Furthermore, I will report on first kinetic simulations of photon production in the expanding Glasma that will quantify our estimates.
RIKEN Lunch Seminar
"From small to moderatex: beyond the eikonal approximation"
Presented by Andrey Tarasov, BNL
Thursday, January 26, 2017, 12:30 pm
Building 510, Room 1224
Hosted by: Hiromichi Nishimura
In recent years significant progress has been made in our understanding of the smallx physics beyond the eikonal approximation. Rigorous analysis of the dependence on the transverse momentum helps us better understand not only physics of the Regge limit, but to connect it to the kinematic limit of the moderatex as well. I'll describe the technique we used in calculation of TMD evolution observed in the DrellYan process and present some recent results.
RIKEN Lunch Seminar
"Vector mesons and chiral symmetry restoration"
Presented by Fabian Rennecke, Heidelberg University
Thursday, January 19, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Hiromichi Nishimura
Vector mesons play a prominent role for the detection of chiral symmetry restoration in the quarkgluon plasma since their inmedium modifications are directly observable in dilepton spectra. However, a direct connection between their inmedium modifications and chiral symmetry restoration remains elusive. To shed some light on this, I will first address the question how chiral symmetry breaking and the light (vector) mesons emerge from the underlying quarkgluon dynamics. Then, I will present preliminary results on the inmedium spectral functions of the rho and a1 mesons obtained from analytic continuation of Euclidean twopoint functions.
Nuclear Theory/RIKEN Seminar
"Going with the flow: solving sign problems in complex space"
Presented by Paulo Bedaque, University of Maryland
Friday, January 13, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
We discuss a new approach to solve the sign problem arising in the Monte Carlo evaluation of path integrals. It is based on deforming the contour of integration into complex space. We will argue that for conceptual and numeric reasons it may be advantageous not to use the steepest descent manifolds (thimbles). We will discuss a variety of algorithms and their application to field theories with a fermionic sign problem and to quantum mechanical models, including real time dynamics.
RIKEN Lunch Seminar
"Plasmon mass scale and linearized gauge field fluctuations in classical YangMills theory"
Presented by Jarkko Peuron, University of Jyvaskyla
Thursday, January 12, 2017, 12:30 pm
Building 510, Room 2160
Hosted by: Heikki Mantysaari
In this talk I discuss the determination of plasmon mass in classical realtime YangMills theory on a lattice in 3 spatial dimensions. I compare 3 different methods to determine the plasmon mass : a hard thermal loop expression in terms of the particle distribution, an effective dispersion relation constructed from fields and their time derivatives, and by measuring oscillations between electric and magnetic field modes after artificially introducing a homogeneous color electric field. Due to plasma instabilities, small quantum fluctuations on top of the classical background may significantly affect the dynamics of the system. I argue for the need for a numerical calculation of a system of classical gauge fields and small linearized fluctuations in a way that keeps the separation between the two manifest. I derive and test an explicit algorithm to solve these equations on the lattice, maintaining gauge invariance and Gauss's law.
Nuclear Theory/RIKEN Seminar
"Prompt atmospheric neutrino flux and forward charm production in protonnucleus collisions"
Presented by Anna Stasto, Penn State
Friday, January 6, 2017, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
The discoveries of the extraterrestrial neutrino flux by IceCube renewed interest in the precise evaluation of the background neutrinos which are produced in the atmosphere due the cosmic ray interactions. One of the most relevant processes at high energies is the charm and beauty production in protonnucleus collisions which needs to be evaluated at very high energies where small x effects may become important. I will discuss a recent calculation of the forward charm production in pp and pA, and compare results from different models which include small x effects due to resummation and saturation. Comparison with the LHC data will be presented and nuclear effects on light nuclei will also be discussed. Finally, I will show the resulting prompt neutrino flux and its uncertainties and discuss the potential improvements.
Nuclear Theory/RIKEN Seminar
"Proton fluctuations and multiparticle rapidity correlations"
Presented by Kevin Dusling, PRL
Friday, December 16, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
The effect of intrinsic fluctuations of the proton saturation momentum scale on eventbyevent rapidity distributions in small systems is explored. Saturation scale fluctuations generate an asymmetry in the single particle rapidity distribution in each event resulting in genuine nparticle correlations. We introduce a color domain model that naturally explains the centrality dependence of the twoparticle rapidity correlations recently measured by ATLAS, constraining the probability distribution of saturation scale fluctuations in the proton. Predictions for n=4, 6 and 8 particle rapidity correlations find that the four and eightparticle cumulant change sign at intermediate multiplicities, a signature which could be tested experimentally.
Nuclear Theory/RIKEN Seminar
"Hydrodynamics, the gradient expansion and transient modes"
Presented by Michal Heller, Perimeter Institute
Friday, December 9, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
I will discuss recent developments at the interplay between hydrodynamic gradient expansion and transient modes in expanding plasma.
RIKEN Lunch Seminar
"Analytic Results for Color Glass In SpaceTime Coordinates"
Presented by Rainer Fries, Texas A&M University
Thursday, December 8, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Heikki Mantysaari
I will start by reviewing some previous results for the McLerranVenugopalan model for nuclear collisions solved analytically in spacetime coordinates. I will then discuss some recent work on initial angular momentum in the resulting YangMills system, which leads to an interesting picture of gluon flow in the event plane. I will also describe further evolution of these results in fluid dynamics. Time permitting I will touch on ongoing efforts to construct an event generator based on analytic solutions.
Nuclear Theory/RIKEN Seminar
"Squeeze Out"
Presented by Ron Longacre, BNL
Wednesday, December 7, 2016, 11 am
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
Squeeze out happen when the expanding central fireball flows around a large surface flux tube in a central AuAu collision at RHIC. We model such an effect in a flux tube model. Two particle correlations with respect to the $v_2$ axis formed by the soft fireball particles flowing around this large flux tube is a way of measuring the effect.
Nuclear Theory/RIKEN Seminar
"Renormalizationgroup flow of the effective action of cosmological largescale structures"
Presented by Stefan Flörchinger, Heidelberg
Friday, December 2, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
The large scale structure of the universe forms a particular type of fluid which is governed by the properties of dark matter. I discuss how one can derive renormalization group equations for the effective action that describes the statistical properties of this fluid. Taking into account in particular effective viscosity and sound velocity terms leads to an improved framework to determine density and velocity power spectra.
HET/RIKEN Seminars
"Heavy meson decays to light resonances"
Presented by Luka Leskovec, University of Arizona
Wednesday, November 30, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Mattia Bruno
Lattice QCD calculations of electroweak decays with single, stronginteractionstable hadrons in the initial and final state have recently reached a high level of precision. Many phenomenologically important decays, however, involve hadronic resonances, and their naive analysis on the lattice leads to uncontrolled systematic errors. Recent theoretical developments in the finitevolume treatment of $1 \to 2$ transition matrix elements now enable us to perform rigorous lattice calculations of electroweak decays to light resonances such as the $\rho$. After presenting the BricenoHansenWalkerLoud formalism, I will discuss our numerical implementation for the $D\to\rho \ell \nu$ and $B\to\rho \ell \nu$ decays, where we aim to quantify the effect of the unstable nature of the $\rho$. Our calculations are performed on a gauge ensemble with 2+1 flavors of clover fermions with a pion mass of ~320 MeV and a lattice size of ~3.6 fm.
Nuclear Theory/RIKEN Seminar
"Phase structure and dynamics of dense QCD"
Presented by Armen Sedrakian, Frankfurt
Friday, November 18, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
In the first part of the talk I will discuss recent computations of the transport coefficients of dense QCD from the Kubo formalism on the basis of a twoflavor model of QCD. The second part of the talk will discuss the properties of compact stars featuring color superconducting phases of dense QCD. This will include modeling of massive compact stars, neutrino cooling of such stars, and possible signatures of a phase transition within the QCD phase diagram in the Xray data from the young neutron star in Cassiopea A.
Nuclear Theory/RIKEN Seminar
"Quantumfieldtheoretical approach to shear and bulk relaxation times"
Presented by Alina Czajka, McGill
Thursday, November 17, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Heikki Mantysaari
The shear and the bulk relaxation times are important ingredients of the second order hydrodynamics whose success in heavy ion phenomenology is unquestioned. Unlike viscosites themselves, field theoretical calculations of the relaxation times are hard to come by in literature, especially for the bulk relaxation time. In this talk, we report two fieldtheoretical analyses involving the shear and the bulk relaxation time. First, by carefully examining the analytic structure of the stressenergy tensor response functions, we have been able to derive, for the first time, a Kubo formula involving both the shear and the bulk relaxation times. Second, by evaluating the Kubo formula within the massless scalar theory, we have so far been able to calculate the shear relaxation time in a simple form. We will then show how this calculation can be extended to calculate the bulk relaxation time as well.
Nuclear Physics & RIKEN Theory Seminar
"Glue spin from lattice QCD"
Presented by YiBo Yang, University of Kentucky
Friday, November 4, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Heikki Mantysaari
I will present the result of the glue spin in proton from the lattice QCD simulation, and also the renormalization and matching issues. The lattice calculation is carried out with valence overlap fermions on 2+1 flavor DWF gauge configurations on four lattice spacings and four volumes including an ensemble with physical values for the quark masses. The glue spin $S_G$ in the $\overline{\text{MS}}$ scheme is obtained with the 1loop perturbative matching. I will also discuss the generic strategy and possible difficulties of calculating the glue helicity on the lattice, from the large momentum effective theory to the lattice simulations.
RIKEN Lunch Seminar
"Form Invariance, Topological Fluctuations and Mass Gap of YangMills Theory"
Presented by Yachao Qian, Stony Brook University
Thursday, November 3, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Hiromichi Nishimura
We study the quantum YangMills theory in the presence of topologically nontrivial backgrounds. The topologically stable gauge fields are constrained by the form invariance condition and the topological properties. Obeying these constraints, the known classical solutions to the YangMills equation in the 3 and 4dimensional Euclidean spaces are recovered, and the other allowed configurations form the nontrivial topological fluctuations at quantum level. Together, they constitute the background configurations, upon which the quantum YangMills theory can be constructed. We demonstrate that the theory mimics the Higgs mechanism in a certain limit and develops a mass gap at semiclassical level on a flat space with finite size or on a sphere.
RIKEN Lunch Seminar
"Hybrid approach to relativistic heavyion collisions at the RHIC BES energies"
Presented by Chun Shen, BNL
Thursday, October 27, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Hiroshi Oki
Using a hybrid (viscous hydrodynamics + hadronic cascade) framework, we model the bulk dynamics of relativistic heavyion collisions at the RHIC BES collision energies, including the effects from nonzero net baryon current and its dissipative diffusion during the evolution. The framework is in full 3+1 dimension which allows us to study the nontrivial longitudinal structure and dynamics of the collision systems, for example, the baryon stopping/transport. The collision energy dependence of hadronic chemistry, identified particle spectra, anisotropic flows, and HBT radii is studied from 200 GeV to 19.6 GeV. Effects of breaking boostinvariance, netbaryon current, and its related diffusion on hadronic observables will be addressed. Finally, flow prediction for recent d+Au collisions at the BES energies will be presented within the same framework.
Special Nuclear Theory/RIKEN seminar
"A new relativistic viscous hydrodynamics code for highenergy heavyion collisions"
Presented by Chihi Nonaka, Nagoya University, Japan
Wednesday, October 26, 2016, 11 am
Small Seminar Room, Bldg. 510
Hosted by: Chun Shen
Relativistic hydrodynamic simulations play a key role in exploring the QGP bulk property and the QCD phase transition from analyses of highenergy heavyion collisions at RHIC and LHC. From the intensive study based on relativistic viscous hydrodynamic models with eventbyevent initial fluctuations, we can extract detailed information of the bulk feature of the QGP such as transport coefficients and the QCD equations of states. In the quantitative analyses of the QGP property, highprecision numerical treatment on the hydrodynamic calculation is important. Recently, we developed a new 3+1 dimensional relativistic viscous hydrodynamics code in Cartesian coordinates. In the algorithm, we use a Riemann solver based on the twoshock approximation which is stable under existence of large shock waves. We extend the algorithm in Cartesian coordinates to that in Milne coordinates so that we can efficiently apply it to the analyses of relativistic heavyion collisions. We check the correctness of the numerical algorithm by comparing numerical calculations and analytical solutions in various problems for ideal and viscous fluids. The new numerical scheme is stable even with small numerical viscosity, which is very important to discuss the physical viscosities at RHIC and LHC.
RIKEN Lunch Seminar
"Chiral magnetic effect and anomalous transport from realtime lattice simulations"
Presented by Niklas Mueller, Heidelberg University
Thursday, October 20, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Hiroshi Oki
We present a firstprinciples study of anomaly induced transport phenomena by performing realtime lattice simulations with dynamical fermions coupled simultaneously to nonAbelian SU(Nc) and Abelian U(1) gauge fields. Investigating the behavior of vector and axial currents during a sphaleron transition in the presence of an external magnetic field, we demonstrate how the interplay of the chiral magnetic and chiral separation effect leads to the formation of a propagating wave. We further analyze the dependence of the magnitude of the induced vector current and the propagation of the wave on the amount of explicit chiral symmetry breaking due to finite quark masses. Further we perform simulations using overlapfermions for the first time in realtime, showing that in the classical statistical regime they can be related to the Wilson formulation.
RIKEN Lunch Seminar
"KibbleZurek dynamics and universal offequilibrium scaling of critical cumulants in the QCD phase diagram"
Presented by Raju Venugopalan, BNL
Thursday, October 13, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Hiroshi Oki
We exploit the universality between the QCD critical point and the three dimensional Ising model to derive closed form expressions for nonequilibrium critical cumulants on the crossover side of the critical point. Novel expressions are obtained for the nonGaussian Skewness and Kurtosis cumulants; our results reveal that they can differ both in magnitude and sign from equilibrium expectations. We show further that key elements of the KibbleZurek framework of nonequilibrium phase transitions can be employed to describe the dynamics of these critical cumulants. As a consequence, observables sensitive to critical dynamics in heavyion collisions are expressible as universal scaling functions and thereby provide powerful model independent guidance in searches for the QCD critical point.
RIKEN Lunch Seminar
"Complex spectrum of QCD at finite density"
Presented by Hiromichi Nishimura, RBRC
Thursday, October 6, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Hiroshi Oki
We consider the effective action of the Polyakov loop at finite temperature and density. Using simple models, we show two novel manifestations of the sign problem in QCD: the nonhermitian transfer matrix and the complex saddle point. As a result the mass matrix associated with the Polyakov loop becomes complex, and it gives rise to damped oscillatory behavior in Polyakov loop correlation functions, which reflects oscillatory behavior in the quarknumber density reminiscent of densitydensity correlation functions in liquids. The complex spectrum should be observable in lattice simulations of QCD and may provide a test for finitedensity algorithms.
RIKEN Lunch Seminar
"Quark Polarization at Small x"
Presented by Matt Sievert, BNL
Thursday, September 15, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Hiroshi Oki
Parton distribution functions in the smallx limit have long been known to be dominated by gluon bremsstrahlung produced in the BFKL and BK / JIMWLK evolution mechanisms. This smallx gluon cascade generates high colorcharge densities, leading to the effective semiclassical theory known as the colorglass condensate (CGC). While this unpolarized smallx evolution has been thoroughly studied, the evolution of the polarized parton distributions is much less understood. Using modern CGC techniques, we calculate the smallx evolution equations for the helicity distribution of polarized quarks. This polarized smallx evolution is quite different from the unpolarized evolution, bringing in much more complicated dynamics which transfer spin to small x. Although the quark polarization at small x is initially suppressed, strong evolution corrections substantially enhance the amount of spin at small x. By solving our equations (numerically, in the largeNc limit), we compute the asymptotic behavior of the quark helicity at small x, and we discuss the implications of this result for the outstanding Proton Spin Puzzle.
RIKEN Lunch Seminar
"Photonjet Ridge at RHIC and the LHC"
Presented by Amir Rezaeian, The Federico Santa Maria Technical University
Thursday, August 4, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Hiroshi Oki
I will talk about inclusive prompt photon and photonjet production in p+A collisions at RHIC and the LHC. In particular, I show that photonjet correlations in the Color Glass Condensate (CGC) picture exhibit longrange azimuthal collimation at nearside for low transverse momenta of the produced photon and jet in highmultiplicity events. These ridgelike features are strikingly similar to the observed ridge effect for dihadron correlations at RHIC and the LHC. I show that correlations in the relative rapidity and the relative azimuthal angle between pairs of prompt photon and jet strongly depend on the gluon saturation dynamics at smallx kinematics and such measurements can help to understand the true origin of the observed dihadron ridge in p+A collisions, and address whether the ridge is a universal phenomenon for all two particle correlations at high energy and high multiplicity events.
RIKEN Lunch Seminar
"CME in Chiral Viscous Hydrodynamics"
Presented by Shuzhe Shi, Indiana University
Thursday, July 14, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Hiroshi Ohki
Anomalous chiral transport processes, with the notable examples of Chiral Magnetic Effect (CME) and Chiral Magnetic Wave (CMW), are remarkable phenomena that stem from highly nontrivial interplay of QCD chiral symmetry, axial anomaly, and gluonic topology. The heavy ion collisions, in which topological fluctuations generate chirality imbalance, and very strong magnetic fields $\vec{\bf B}\sim m_\pi^2$ are present during the early stage of such collisions, provide a unique environment to study these anomalous chiral transport processes. Significant experimental efforts have been made to look for signals of CME and various other signals of anomalous chiral transport effects in heavy ion collisions. Crucial for such efforts, is the theoretical development of quantitative simulations based on hydrodynamics that incorporates chiral anomaly, implements realistic initial conditions and properly accounts for possible backgrounds. We will introduce our recent progress to understand CME qualitatively, based on a 2+1D viscous hydrodynamics framework
RIKEN Lunch Seminar
"Kondo effect in QCD"
Presented by Sho Ozaki, Keio University
Thursday, June 30, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Hiroshi Oki
In condensed matter physics, Kondo effect is known as an enhancement of electrical resistance of impure metals with decreasing temperature/energy. This phenomenon is the first known example of asymptotic freedom in physics, which is found well before the discovery of that of QCD. Kondo effect is caused by the combination of the following ingredients: In addition to the existence of a heavy impurity, (i) Fermi surface, (ii) quantum fluctuations (loop effects), (iii) nonAbelian nature of interaction (e.g. spinflip interaction in the case of condensed matter physics). In this talk, I will discuss Kondo effect realized in QCD. We found the characteristic behavior of Kondo effect in quark matter with heavy quark impurity. There, the color exchange interaction mediated by gluons plays the role of the third condition (iii) for the appearance of Kondo effect. Furthermore, we found a novel type of Kondo effect induced by strong magnetic fields. In addition to the fact that the magnetic field dose not affect the color degrees of freedom, dimensional reduction to 1+1 dimensions and degenerate quarks in lowest Landau level play essential role for the magnetically induced QCD Kondo effect.
Nuclear/Riken Theory Committee
"On Pressure Isotropization in HeavyIon Collisions"
Presented by Bin Wu, The Ohio State University
Friday, June 24, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
In this talk, I would like to start with a brief introduction to nonequilibrium quantum field theory in the SchwingerKeldysh formalism. This formalism provides a systematic way to study isotropization and other timedependent nonequilibrium (and equilibrium) phenomena in heavyion collisions. I shall first discuss the foundation of classical field approximations (CSA), which is an important tool to study the evolution at very early stages. It is, however, found to be nonrenormalizable. This helps us understand better the applicability of such an approximation. it is now wellknown that isotropization can not be established before the breakdown of the CSA. We then use another approximation, the quasiparticle approximation (the Boltzmann equation), to study the isotropization in a scalar field theory. Our result shows explicitly the importance of quantum effects. Motivated by these observations, we have been studying whether the isotropization can be reached before the dense system of gluons, produced in the collisions of two big nuclei, becomes too dilute to be studied perturbatively in the SchwingerKeldysh formalism. Some preliminary results shall be reported.
RIKEN Lunch Seminar
"Lefschetzthimble path integral for studying the sign problem and Silver Blaze phenomenon"
Presented by Yuya Tanizaki, RBRC
Thursday, May 26, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Hiroshi Ohki
Recently, PicardLefschetz theory gets much attention in the context of the sign problem, because it enables us to study the system with the complex classical action nonperturbatively by employing the semiclassical analysis. In this seminar, after its brief introduction, I will apply it to the onesite Hubbard model. This model has a severe sign problem, which looks quite similar to that of the finitedensity QCD at low temperatures. By solving this model using the Lefschetzthimble path integral, we are trying to understand the structure of the sign problem of finitedensity QCD. Especially, I give a qualitative picture (or speculation) about the earlyonset problem of the baryon number density, called the baryon Silver Blaze problem. The complex Langevin method will also be discussed if time allows.
Nuclear Theory/RIKEN Seminar
"The jet quenching parameter qhat, and its relation to the TMDPDF"
Presented by Abhijit Majumdar, Wayne State University
Friday, May 20, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Based on prior work by the JET collaboration, the importance of the factorization and scale evolution of the jet quenching parameter qhat will be outlined. This will turn out to be important for both phenomenological extractions of qhat as well as for first principle determinations on the lattice. I will argue that for jets at RHIC and LHC, qhat does not lie within the range of Bjoerkenx where small x effects would be considered to be dominant. Given this situation, qhat will be found to be an integral over an operator product separated in both lightcone and transverse distance, but somewhat different from a ``traditional'' TMDPDF. This new distribution will be studied at NexttoLeading Order and the fate of nonstandard divergences discussed.
RIKEN Lunch Seminar
"KosterlitzThouless transition and chiral rotation in external electromagnetic field"
Presented by Gaoqing Cao, Fudan University
Thursday, May 19, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Daniel Pitonyak
In 2+1 dimensional system, the most important phase transition should be of the KosterlitzThouless (KT) type. We determined the KT transition temperature T_KT as well as the mass melting temperature T^* as a function of the magnetic field. It is found that the pseudogap domain T_KT < T < T^* is enlarged with increasing strength of the magnetic field. The influence of a chiral imbalanceμ_5 was also studied. We found that even a constant axial chemical potential μ_5 can lead to inverse magnetic catalysis of the KT transition temperature in 2+1 dimensions. This is actually the de Haas—van Alphen oscillation. Furthermore, we studied the QCD vacuum structure under the influence of an electromagnetic field with a nonzero second Lorentz invariant I_2=E·B. We showed that the presence of I_2 can induce neutral pion (π_0) condensation in the QCD vacuum through the electromagnetic triangle anomaly. Within the frameworks of chiral perturbation theory at leading smallmomenta expansion as well as the Nambu—JonaLasinio model at leading 1/Nc expansion, a universal dependence of the π_0 condensate on I_2 was found. The stability of the π_0condensed vacuum is also discussed.
HET/RIKEN Seminar
"Higgs Pair Production in Extensions of the Standard Model"
Presented by Ramona Groeber, Roma Tre
Wednesday, May 18, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Pier Paolo Giardino
Higgs pair production is not only interesting as a probe of the trilinear Higgs selfcoupling, but beyond the Standard Model physics can influence the Higgs pair production cross section in many different ways, for example by new couplings, new loop particles or new resonances. In this talk, I will address the question whether we could see for the first time deviations from the Standard Model in Higgs pair production assuming that no deviations were seen before. Furthermore, for certain models I will show how higher order corrections influence the cross section.
Nuclear Theory/RIKEN Seminar
"Evolution of the jet opening angle distribution in holographic plasma"
Presented by Andrei Sadofyev, MIT
Friday, May 13, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Energetic jets are particularly interesting probes of QGP created in heavy ion collisions. Recently a lot of progress was made in attempting to describe the jet evolution in holography. In this talk I'll present an application of a simple dual model to study the jet substructure starting with energy and angle distributions from pQCD. In particular I will show that there are two competing effects: (1) each individual jet widens as it propagates through plasma; (2) the final jet opening angle distribution becomes narrower since wider jets lose more energy and less likely to survive. So, the mean opening angle for jets with a given energy can easily shift toward smaller angles, even while every jet in the ensemble broadens.
RIKEN Lunch Seminar
"The Functional Renormalization Group Method and Delayed Magnetic Catalysis"
Presented by Stefan Rechenberger, University of Darmstadt
Thursday, May 12, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Daniel Pitonyak
This talk will start with a very general introduction to the Functional Renormalization Group method, a powerful nonperturbative tool which can be applied to various problems. The second part of the talk will demonstrate this by discussing the influence of an external magnetic field on the chiral phase transition in the theory of strong interaction. The Functional Renormalization Group analysis shows that, driven by gluon dynamics, the chiral critical temperature decreases for small values of the magnetic field. For large values of the external field, however, the phase transition temperature increases.
HET/RIKEN Seminar
"Axions and Topology"
Presented by Simon Mages, Forschungszentrum Juelich
Wednesday, May 11, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Tomomi Ishikawa
This talk will be centered around the calculation of the high temperature topological susceptibility in QCD. It will provide some background on our motivation from cosmology and particle physics, which is the dependence of axion physics on nonperturbative QCD. I will show our recent results on the quenched high temperature topological susceptibility and discuss difficulties with this conventional approach, which render dynamical studies unfeasible. I will also present our new approach based on formulating QCD on a nonorientable manifold, which is a promising candidate to solve issues related to topological freezing and the divergence of autocorrelations when approaching the continuum limit.
Nuclear Theory/RIKEN seminar
"Fluid dynamics for the anisotropically expanding quarkgluon plasma"
Presented by Dennis Bazow, The Ohio State University
Friday, May 6, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Local momentum anisotropies become large in the early stages of the quarkgluon plasma created in relativistic heavyion collisions, due to the extreme difference in the longitudinal and transverse expansion rates. In such situations, fluid dynamics derived from an expansion around an isotropic local equilibrium state is bound to break down. Instead, we subsume the slowest nonhydrodynamic degree of freedom (associated with the deviation from momentum isotropy) at leading order defining a local anisoptropic quasiequilibrium state, thereby treating the longitudinal/transverse pressure anisotropy nonperturbatively. Perturbative transport equations are then derived to deal with the remaining residual momentum anisotropies creating a complete transient effective theory called viscous anisotropic hydrodynamics. This approach has been shown to dramatically outperform viscous hydrodynamics in several simplified situations for which exact solutions exits but which share with realistic expansion scenarios the problem of large dissipative currents. We will discuss the present status of applying viscous anisotropic hydrodynamics to the phenomenological description of the quarkgluon plasma in realistic expansion scenarios.
RIKEN Lunch Seminar
"Vorticity in heavyion collisions and cold atoms"
Presented by XuGuang Huang, Fudan University
Thursday, May 5, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Daniel Pitonyak
Vorticity describes the local rotation of the fluid. I will talk about our recent study of the eventbyevent generation of flow vorticity in heavyion collisions. Several special properties of the vorticity in heavyion collisions will be discussed, e.g., the impact parameter dependence, the collision energy dependence, the spatial distribution, the eventbyevent fluctuation of the magnitude and azimuthal direction. Vorticity can drive vector and axial current in chiral quarkgluon plasma via the chiral vortical effect. I will discuss the collective gapless mode, the chiral vortical wave, emerging from CVE and its experimental implications in heavyion collisions. Finally, I will consider the rotating trapped cold atomic gases and show that when there is a Weyl spinorbit coupling such cold atomic gases provide a desktop simulator of the chiral magnetic effect and chiral separation effect.
Nuclear Theory/RIKEN Seminar
"Going with the flow: sign problem, Lefschetz thimbles and beyond"
Presented by Gokce Basar, University of Maryland
Friday, April 29, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Monte Carlo method, a robust way of studying field theories and many body systems, suffers from the sign problem when the action is complex. This includes an important set of problems such as most field theories, including QCD, and strong correlated electronic systems at finite density, as well as computation of real time quantities like transport coefficients. I will show that lifting the path integration to a complex manifold provides a way to ameliorate the sign problem, and introduce a new algorithm for carrying on such a computation. I will give some quantum mechanical examples with severe sign problems, including finite density of fermions and real time observables where Monte Carlo simulations can be profitably performed by this method. Finally I will discuss the 3+1d Bose gas with nonzero chemical potential.
RIKEN Lunch Seminar
"Solving QCD2"
Presented by Alexei Tsvelik, BNL
Thursday, April 28, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Daniel Pitonyak
We study a (1+1)dimensional version of the famous NambuJonaLasinio model of Quantum Chromodynamics (QCD2) both at zero and finite chemical potential. We use non perturbative techniques (nonAbelian bosonization and Truncated Conformal Space Approach). At zero chemical potential we describe a formation of fermion threequark (nucleons and ?baryons) and boson (twoquark mesons, sixquark deuterons) bound states and also a formation of a topo logically nontrivial phase. When the chemical potential exceeds the critical value, the model has a rich phase diagram which includes phases with density wave and superfluid quasilongrange (QLR) order and also a phase of a baryon TomonagaLuttinger liquid (strange metal). The QLR order results as a condensation of scalar mesons (the density wave) or sixquark bound states (deuterons).
HET/RIKEN Seminar
"Heavy Higgs Resonance Dip"
Presented by Sunghoon Jung, SLAC
Wednesday, April 27, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Cen Zhang
We discuss overlooked resonance shapes of heavy Higgs bosons that arise from the resonancecontinuum interference with a complex phase. They include pure resonance dips and nothingness. We derive conditions under which they are produced and we modify narrow width approximation suitable for them. We then discuss how MSSM heavy Higgs searches at the LHC can be challenged and changed.
RIKEN Lunch Seminar
"Color fluctuation phenomena in high energy hadron & photonA collisions"
Presented by Mark Strikman, Penn State University
Thursday, April 21, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Daniel Pitonyak
Compositeness of the bound states and the Lorentz slowing down of high energy interactions in QED and QCD lead to emergence of new coherent phenomena. We focus on the phenomena related to the fluctuations of the strength of interaction (color fluctuations phenomena). First we consider gross violations of the Glauber model for centrality dependence of production of the leading jets in pA scattering predicted earlier within QCD and recent evidence for this phenomenon from the studies of hard pA collisions at the LHC and dAu collisions at RHIC. Color fluctuations also explain a large suppression of the cross section of coherent vector meson photoproduction as compared to the Glauber model observed recently in the ultraperipheral collisions at LHC. We outline perspectives of future studies of the color fluctuation phenomenon in ultraperipheral heavy ion collisions at the LHC and electron  nucleus colliders.
Nuclear Theory/RIKEN seminar
"Vorticular fluid and Lambda Polarization in Highenergy Heavyion Collisions"
Presented by XinNian Wang, LBNL/CCNU
Friday, April 15, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
The strongly coupled quarkgluon plasma created in highenergy heavyion collisions has rich vortical structures that are caused by global total orbital angular momentum and transverse evolution of longitudinal flow. Fermions (quarks in sQGP phase and baryons in the hadronic phase) in such a vorticular fluid are naturally polarized due to spinorbital. I will discuss both local and global quark polarization and how one can use the lambda polarization in the final state to study the vortical structure and constrain the transport properties of sQGP.
Nuclear Theory/RIKEN seminar
"Studying Nucleons in Soliton Models"
Presented by Song Shu, Stonybrook University
Friday, April 1, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Both chiral solitons and confined solitons are discussed at finite temperatures and densities in effective models. Based on the solitons the nucleon properties are studied in thermal medium. The nucleon mass in medium is carefully calculated. It is showed that the chiral solitons could even survive after the chiral phase transition, while confined solitons collapse after the system is deconfined.
RIKEN Lunch Seminar
"Sphalerons Far From Equilibrium and Associated Phenomena"
Presented by Mark Mace, Stony Brook University
Thursday, March 31, 2016, 12:30 pm
Building 510 Room 2160
Hosted by: Daniel Pitonyak
In this talk, I will present a first computation of sphalerons in the glasma; the highly occupied, weakly coupled gluon dominated preequilibrium matter created at early times after an ultrarelativistic heavy ion collisions. The sphaleron transition is a well known ingredient in the generation of anomalous vector current from a strong external magnetic field, the socalled Chiral Magnetic Effect. We perform classicalstatistical realtime lattice simulations to study the dynamics of these topological transitions; simplifying our description by employing SU(2) gauge fields and neglecting the longitudinal expansion for this first study. I will show that the nonequilibrium sphaleron transition rate is time dependent and nonMarkovian, in addition to being dominant in comparison to the thermal equilibrium sphaleron transition rate. In addition, we can measure the scaling and separation of physical scales in analogy to those from thermal equilibrium, in order to parameterize this rate and understand the approach to equilibrium. I will then demonstrate that it is the magnetic screening length, which we extract nonperturbatively, that controls this rate. Additionally, I will briefly mention studies of related anomalous transport effects that we plan on studying using this first principles classicalstatistical realtime lattice technology.
Special RIKEN/HET Seminar
"Axion Phenomenology from Unquenched Lattice QCD"
Presented by Guido Martinelli, Rome University
Thursday, March 24, 2016, 11 am
Large Seminar Room, Bldg. 510
Hosted by: Hiroshi Oki
We investigate the topological properties of Nf = 2 + 1 QCD with physical quark masses, both at zero and finite temperature. At zero temperature both finite size and finite cutoff effects have been studied by comparing the continuum extrapolated results for the topological susceptibility χ with the predictions from chiral perturbation theory. At finite temperature, we explore a region going from Tc up to around 4Tc, where continuum extrapolated results for the topological susceptibility and for the fourth moment of the topological charge distribution are obtained. While the fourth moment converges to the dilute instanton gas prediction the topological susceptibility differs strongly both in the size and in the temperature dependence. This results in a shift of the axion dark matter window of almost one order of magnitude with respect to the instanton computation.
Nuclear Theory/RIKEN Seminar
"Duality, Dimensions and Reduction on the Lattice"
Presented by Joel Giedt, Rensselaer Polytechnic Institute
Friday, March 18, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Montonen and Olive found evidence that a duality could exist in YangMills with adjoint scalars. In this scheme, the 't HooftPolyakov monopole forms a gauge triplet with the photon, leading to a theory equivalent to the GeorgiGlashow model but with magnetic charge replacing electric charge. The duality is believed to be realized in N=4 superYangMills. We are pursuing numerical, nonperturbative evidence for this Sduality using our lattice formulation. Two lines of approach are being taken, which I will discuss. First, we attempt to show that there is a value of the gauge coupling for which the W boson mass is equal to the monopole mass. Second, we are relating the 't Hooft loop to the Wilson loop at this selfdual coupling. On a somewhat unrelated topic, we also discuss the determination of anomalous dimensions on the lattice. In the dual gravitational picture these correspond to masses of fields in the bulk, so that some aspects of the gaugegravity duality could be tested by such determinations. In particular in N=4 superYangMills there are predictions for the dimensions of nonprotected operators at the selfdual point, based on the superconformal bootstrap.
RIKEN Lunch Seminar
"Investigation of anomalous dynamics and the Chiral Magnetic Effect far from equilibrium"
Presented by Niklas Mueller, University of Heidelberg
Thursday, March 3, 2016, 12:30 pm
Building 510, Room 2160
Hosted by: Daniel Pitonyak
We investigate the impact of the AdlerBellJackiw axial anomaly on the realtime dynamics of gauge theories in the strong field regime. By studying and comparing Abelian gauge theories, such as QED, with nonAbelian systems, we try to clarify the role of topological properties and initial conditions relevant far from equilibrium. We show that the Abelian version of the Chiral Magnetic Effect, which has been predicted in the context of ultrarelativistic heavy ion collisions, can result in nontrivial experimental signatures, which could possibly be observed in future highintensity laser experiments. Further I will report on recent investigations of chiral production mechanisms in strong nonAbelian gauge fields and I will discuss the influence of topological objects such as sphalerons, far from equilibrium. Moreover I will show first results of the studies we have undertaken since my arrival here at BNL and discuss how the combination of these studies might be used to shed more light on the role played by anomalies in the early stages of a heavy ion collision.
Nuclear Theory/RIKEN Seminar
"Real time method of thermal field theory"
Presented by Samir Mallik, Saha Institute of Nuclear Physics
Friday, February 26, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
I review the basic ideas of real time formulation of thermal field theory. Then I like to consider the following topics in this formulation: 1) thermal propagator for a scalar field 2) spectral representation of twopoint functions for arbitrary fields 3) perturbation expansion 4) oneloop self energy 5) dilepton production
RIKEN Lunch Seminar
"Lambda_c  N interaction from lattice QCD"
Presented by Takaya Miyamoto, Yukawa Institute for Theoretical Physics, Kyoto University
Thursday, February 25, 2016, 12:30 pm
Building 510 Room 2160
Hosted by: Hiroshi Oki
Recently, a new approach to investigate hadron interactions in lattice QCD has been proposed[1] and developed extensively by the HAL QCD Collaboration[2]. This method can be easily applied to heavy baryon systems even though it is difficult to obtain experimental data of heavy baryons. We have investigated the interaction between Lambda_c and nucleon (N) from lattice QCD using the HAL QCD method. This is the first step to understand charmedbaryon interaction in lattice QCD. In this talk, we present the current status of our research project onLambda_cN interactions as well as future prospects. This talk is based on PoS (LATTICE 2015) 090.
Nuclear Theory/RIKEN Seminar
"Lattice QCD investigations of quark transverse momentum in hadrons"
Presented by Michael Engelhardt, New Mexico State University
Friday, February 19, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
An ongoing program of evaluating transverse momentum dependent parton distributions (TMDs) within lattice QCD is reviewed, summarizing recent progress with respect to several challenges faced by such calculations. These lattice calculations are based on a definition of TMDs through hadronic matrix elements of quark bilocal operators containing stapleshaped gauge connections. A parametrization of the matrix elements in terms of invariant amplitudes serves to cast them in the Lorentz frame preferred for a lattice calculation. Results presented include data on the naively Todd Sivers and BoerMulders effects, as well as the transversity and a wormgear distribution. Correlating quark transverse momentum with impact parameter, one can extract quark orbital angular momentum directly,including both the Ji as well as the JaffeManohar definitions.
Nuclear/Riken Theory Seminar
"The Transverse Structure of the Nucleon"
Presented by Marc Schlegel, University of Tuebingen
Friday, February 19, 2016, 11 am
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Perturbative QCD based on the Parton Model of the nucleon is a very successful theoretical approach to describe highenergy processes at particle accelerators and colliders. In particular, parton distribution functions are key ingredients of this approach and give information on the partonic substructure of the nucleon. As such they deliver a onedimensional picture of how the parton momenta are distributed in the nucleon. In this talk extensions of the parton model are presented which provide access to more detailed information on the dynamics of partons in the nucleon. In particular observables involving transversely polarized nucleons are discussed. They can be described in terms of dynamical quarkgluon correlations which in turn can be studied at an ElectronIon Collider. Another extension of the parton model takes into account the intrinsic transverse motion of the partons. In this approach  called Transverse Momentum Dependent (TMD) factorization  one can study threedimensional distributions of the parton momenta. In addition, implications of the transverse motion of gluons in the nucleon will be discussed for LHC physics.
Nuclear Theory/RIKEN Seminar
"Understanding the structure of hadrons through spin observables in hardscattering processes"
Presented by Daniel Pitonyak, BNL
Friday, February 12, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Almost all of the visible matter in the universe is built from hadrons, which are composed of quarks and gluons. One of the main challenges in nuclear physics is to understand this complex internal structure. In this talk, I will discuss how hardscattering processes that involve the spin of hadrons give us insight into aspects of their innerworkings that otherwise would be inaccessible. I will focus on phenomena that arise when hadrons carry spin transverse to their direction of motion, which allow us to examine them in 3D and analyze correlations between their quarks and gluons. I will also consider a new attempt to resolve the socalled "spin crisis" of how the proton gets its spin by looking at how much spin can be carried by smallx quarks and gluons.
RIKEN Lunch Seminar
"Kinetic regime of hydrodynamic fluctuations"
Presented by Yukinao Akamatsu, Stony Brook University
Thursday, February 4, 2016, 12:30 pm
Building 510 Room 2160
Hosted by: Hiroshi Ohki
Hydrodynamics is an effective theory of systems close to equilibrium. It has been applied to description of fireballs created in the heavyion collisions. With growing interests in fluctuation of observables, theoretical identification of its origin is crucial. One of such origins is thermal fluctuation required by the fluctuationdissipation theorem. In this talk, I will present a new insight into the thermal fluctuation of hydrodynamics by separating the hard and soft scales in a given background. As an illustration, we adopt the Bjorken expansion as a background. The kinetic description of hard modes allows us simple interpretation of renormalization, longtime tails, and fractional powers of derivative expansion.
Nuclear Theory/RIKEN Seminar
"New aspects of QCD dynamics at high density: Jet evolution in the QGP and wave turbulence""
Presented by Yacine MehtarTani, INT Seattle
Friday, January 29, 2016, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
An essential feature of the parton shower that form a jet evolving in vacuum is color coherence that suppresses large angle soft gluon radiation and thus, ensuing the collimation of the jet. In the presence of dense QCD matter jet constituents suffer a rapid color randomization and thus an alteration of color coherence: as a result a mediuminduced gluon cascade, that can be described by a classical Makovian process, develop at large angles with respect to the jet axis [3]. A remarkable phenomenon emerges from such a cascade: the energy spectrum (of jet constituents) exhibits a scaling behavior, akin to wave turbulence, characterized by a constant flow of energy from the forward energetic patrons towards low momentum gluons down to the temperature of the plasma where energy is dissipated [4]. This picture is in agreement with a recent CMS analysis of missing energy in asymmetric dijet events where the energy balance is recovered at large angles and very soft particles [5]. In the second part of the talk I will discuss radiative corrections to jet observables that were shown to exhibit large double logarithmic enhancements. Owing to a large separation of time scales we have shown that these large corrections can be reabsorbed in a renormalization of the jetquenching parameter q^, preserving the probabilistic picture of the parton cascade [6]. This result leads us to question the standard viewpoints of the coupling of jets to the medium: the naive perturbative approach based on a leading order calculation and the AdS/CFT correspondence for strongly coupled plasmas. I will briefly invoke in the final part of my talk the various questions that remain to be addressed. Indeed, despite the recent progress much remains to be understood about jet fragmentation in a dense medium in order to construct a systematic and predictive approach to jetquenching from first principles.
RIKEN Lunch Seminar
"Confinement and Chiral symmetry breaking from an Interacting Instantondyon ensemble for 2 colors and Nf flavors"
Presented by Rasmus Larsen, Stony Brook University
Thursday, January 14, 2016, 12:30 pm
Building 510 Room 2160
Hosted by: Daniel Pitonyak
I will present numerical results based on an interacting ensemble of instantondyons, that explains the connection between chiral symmetry breaking and confinement. The instantondyons have the nice properties to behave as monopoles at low temperatures, and as instantons at high temperatures. We will see how the scaling behavior of the instantondyons creates a Polyakov loop dependent potential, which forces the Polyakov loop to the confining value as the density of dyons increases at lower temperatures. For 2 flavors we find that the dominating configuration in the ensemble exhibit a chiral symmetry transition at the same temperature as the confinement transition, within accuracy. The important factor in explaining confinement and chiral symmetry breaking is the density of the Instantondyons.
RIKEN Lunch Seminar
"Baryon interactions from Lattice QCD by Luscher's finite volume method and HAL QCD method"
Presented by Takumi Iritani, Stony Brook University
Thursday, December 17, 2015, 12:30 pm
Building 510 Room 2160
Hosted by: Hiroshi Oki
Both Luscher's finite volume method and HAL QCD method are used to analyze the hadronhadron interaction in lattice QCD. However, some systematic discrepancies are reported between them.For example, Luscher's method shows the bound states of both deuteron and dineutron at the heavy pion mass,while these channels are scattering states from HAL QCD method. In this talk, to understand the deviations between them, we investigate the baryon interaction from both methods with the same lattice setups.From a systematic comparison of two methods, we clarify the problems in the previous studies. We also discuss the improvement of the analyses.
Nuclear Theory/RIKEN seminar
"Evolution of gluon TMDs: from small to moderate x"
Presented by Andrey Tarasov, Jefferson Lab
Friday, December 11, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Recently we obtained an evolution equation for gluon TMDs, which addresses a problem of unification of different kinematic limits. It describes evolution in the whole range of Bjorken x and transverse momentum kâŠ¥. I plan to discuss this evolution equation and show how in different kinematic regimes it yields several wellknown and some previously unknown results.
RIKEN Lunch Seminar
"Phase structure of lattice QCD with Wilson and twistedmass fermions including isospin breaking"
Presented by Derek Horkel, University of Washington
Thursday, December 10, 2015, 12:30 pm
Building 510 Room 2160
Hosted by: Hiroshi Oki
As the precision frontier of particle physics continues to develop, the field of lattice QCD has risen to the challenge. Modern lattice simulations, have increasingly included light nondegenerate up and down quark masses and electromagnetism. Previously answered questions about the vacuum structure of QCD on the lattice must be reexamined when these isospin breaking effects are included. If not careful, lattice practitioners may simulate in nonphysical phases which cannot be extrapolated to the continuum limit. Using chiral perturbation theory, I will discuss where these nonphysical phases can arise for Wilson and twisted mass fermions. I will also explain some of the complications which arise when tuning the up and down twisted quark masses to their critical values in the presence of electromagnetism.
Nuclear Theory/RIKEN Seminar
"Semiclassics, complex saddles and real path integrals"
Presented by Tin Sulejmanpasic, North Carolina State University
Friday, December 4, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
I will discuss the use of semiclassics and instanton calculus and argue that, contrary to common wisdom, complex solutions of the equations of motion are a necessary ingredient of any semiclassical expansion. In particular, I will show that without the complex solutions semiclassical expansion of supersymmetric theories cannot be reconciled with supersymmetry. This has a natural interpretation in the PicardLefschetz theory.
RIKEN Lunch Seminar
"Sterile neutrino dark matter produced after the QCD phase transition"
Presented by Louis Lello, University of Pittsburgh
Thursday, December 3, 2015, 12:30 pm
Building 510 Room 2160
Hosted by: Daniel Pitonyak
Sterile neutrinos are SU(2) singlets that mix with active neutrinos via a mass matrix, its diagonalization leads to mass eigenstates that couple via standard model vertices. We study the production of sterile neutrinos in the early universe from pion decays shortly after the QCD phase transition in the absence of a lepton asymmetry. We introduce the quantum kinetic equations that describe their production, freeze out and decay and discuss the various processes that lead to their production in a wide range of temperatures assessing their feasibility as dark matter candidates. We consider the production of heavy neutrinos in the mass range < 140MeV from pion decay shortly after the QCD crossover including finite temperature corrections to the pion form factors and mass. We consider the different decay channels that allow for the production of heavy neutrinos showing that their frozen distribution functions exhibit effects from "kinematic entanglement" and argue for their viability as mixed dark matter candidates. We discuss abundance, phase space density and stability constraints and argue that heavy neutrinos with lifetime >1/H0 freeze out of local thermal equilibrium.
Nuclear Theory/RIKEN Seminar
"Transversity Distribution and Collins Fragmentation Functions with QCD Evolution"
Presented by Alexei Prokudin, Jefferson Lab
Friday, November 20, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
We study the transverse momentum dependent (TMD) evolution of the Collins azimuthal asymmetries in e+eâˆ' annihilations and semiinclusive hadron production in deep inelastic scattering (SIDIS) processes. All the relevant coefficients are calculated up to the nexttoleading logarithmic (NLL) order accuracy. By applying the TMD evolution at the approximate NLL order in the CollinsSoperSterman (CSS) formalism, we extract transversity distributions for u and d quarks and Collins fragmentation functions from current experimental data by a global analysis of the Collins asymmetries in backtoback dihadron productions in e+eâˆ' annihilations measured by BELLE and BABAR Collaborations and SIDIS data from HERMES, COMPASS, and JLab HALL A experiments. The impact of the evolution effects and the relevant theoretical uncertainties are discussed. We further discuss the TMD interpretation for our results, and illustrate the unpolarized quark distribution, transversity distribution, unpolarized quark fragmentation and Collins fragmentation functions depending on the transverse momentum and the hard momentum scale. We make detailed predictions for future experiments and discuss their impact.
HET/RIKEN Lunch Seminar
"Collider Phenomenology of the Right Handed Heavy Neutrinos"
Presented by Arindam Das, University of Alabama
Friday, November 20, 2015, 12 pm
Building 510 Room2160
Hosted by: Amarjit Soni
We study the collider signature of pseudoDirac heavy neutrinos in the inverse seesaw scenario, where the heavy neutrinos with mass at the electroweak scale can have sizable mixings with the Standard Model neutrinos, while providing the tiny light neutrino masses by the inverse seesaw mechanism. Based on a simple, concrete model realizing the inverse seesaw scenario, we fix the model parameters so as to reproduce the neutrino oscillation data and to satisfy other experimental constraints, assuming two typical flavor structures of the model and the different types of hierarchical light neutrino mass spectra. For completeness, we also consider a general parametrization for the model parameters by introducing an arbitrary orthogonal matrix and the nonzero Dirac and Majorana phases. We perform a parameter scan to identify an allowed parameter region which satisfies all experimental constraints. With the fixed parameters, we analyze the heavy neutrino signal at the LHC through trilepton final states with large missing energy and at the ILC through a single lepton plus dijet with large missing energy.
RIKEN Lunch Seminar
"Viscous Velocity Gradient Correction to Thermal Photon Emission Rate at Strong Coupling"
Presented by Kiminad Mamo, University of Illinois at Chicago
Thursday, November 19, 2015, 12:30 pm
Building 510 Room 2160
Hosted by: Daniel Pitonyak
We compute the correction to the thermal photon emission rate in first order of shear components of fluid velocity gradients in nearequilibrium hydrodynamic plasma at strong coupling regime using the realtime SchwingerKeldysh formalism in AdS/CFT correspondence. We find that the gradient correction to the thermal photon emission rate at strong coupling is about 0.3  0.4 times of the equilibrium rate.
Nuclear Theory/RIKEN Seminar
"Linearly resummed hydrodynamics from gravity"
Presented by Yanyan Bu, Ben Gurion University of the Negev
Friday, November 13, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Using fluid/gravity correspondence, we study allorder resummed hydrodynamics in a weakly curved spacetime. The underlying microscopic theory is a finite temperature \mathcal{N}=4 superYangMills theory at strong coupling. To linear order in the amplitude of hydrodynamic variables and metric perturbations, the fluid's stressenergy tensor is computed with derivatives of both the fluid velocity and background metric resummed to all orders. In addition to two viscosity functions, we find four curvature induced structures coupled to the fluid via new transport coefficient functions, which were referred to as gravitational susceptibilities of the fluid (GSF). We analytically compute these coefficients in the hydrodynamic limit, and then numerically up to large values of momenta. We extensively discuss the meaning of all order hydrodynamics by expressing it in terms of the memory function formalism, which is also suitable for practical simulations. We also consider GaussBonnet correction in the dual gravity, which is equivalent to some 1/N corrections in the dual CFT. To leading order in the GaussBonnet coupling, we find that the memory function is still vanishing.
Joint RIKEN Lunch/HET Seminar
"Gluonfusion Higgs production: the final frontier"
Presented by Elisabetta Furlan, ETH, Zurich
Thursday, November 12, 2015, 12:30 pm
Building 510 Room 2160
Hosted by: Tomomi Ishikawa
The gluonfusion Higgs production cross section has been recently computed through the nexttonexttonext to leading order (N^3LO) in QCD. This unprecedented level of accuracy is crucial to exploit fully the LHC data in the validation of the Standard Model and in the search for potential (small) deviations due to new physics. I will give an overview of the tools that we employed to achieve this result, from the framework of heavyquark effective theories to the analytical and mathematical machinery that we developed. I will conclude with some results and future prospects.
Nuclear Theory/RIKEN Seminar
"Massless QED in three dimensions with even number of flavors"
Presented by Rajamani Narayanan, Florida International University
Friday, November 6, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Massless QED in three (two space and one Euclidean time) with even number of flavors does not break parity. There are analytical arguments for chiral symmetry to be spontaneously broken and some numerical evidence supporting these arguments. An interesting "open" question is the possibility of a critical number of flavors below which chiral symmetry is broken. Numerical results obtained using dynamical Wilson fermions will be presented with emphasis on the behavior of the low lying eigenvalues of the Wilson Dirac operator. Finite volume analysis will be used to obtain conclusions about the absence or presence of a chiral condensate.
Nuclear Theory/RIKEN Seminar
"Observable consequences of eventbyevent fluctuations of HBT radii"
Presented by Christopher J. Plumberg, Ohio State University
Friday, October 30, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
One of the major lessons from the field of heavyion physics in the past several years has been the significance of the role played by eventbyevent fluctuations in the evolution of a heavyion collision. Their important effects on many momentumspace observables (particle yields and spectra, anisotropic flows, etc.) have already been studied systematically, and some of the properties of their eventbyevent distributions, and their consequences for the extraction of medium properties such as the specific viscosity of the quarkgluon plasma (QGP), are already known. In this talk it is pointed out that similar eventbyevent fluctuations of spatiotemporal observables provide complementary constraints on our understanding of the dynamical evolution of heavyion collisions. The relation of Hanbury BrownTwiss (HBT) radii extracted from ensembleaveraged correlation function measurements to the mean of their eventbyevent probability distribution is clarified, and a method to experimentally determine the mean and variance of this distribution is proposed and demonstrated using an ensemble of fluctuating events generated with the viscous hydrodynamic code VISH2+1. The sensitivity of the mean and variance of the HBT radii to the specific QGP shear viscosity Î·/s is studied using simulations with the same code. We report sensitivity of the mean pion HBT radii and their variances to the temperature dependence of Î·/s near the quarkhadron transition at a level similar (1020%) to that which was previously observed for elliptic and quadrangular flow of charged hadrons.
Nuclear Theory/RIKEN Seminar
"Thermal photons from a modern hydrodynamical model of heavy ion collisions"
Presented by JeanFrancois Paquet, Stonybrook University
Friday, October 23, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Early fluiddynamical calculations of direct photon spectra and momentum anisotropy were found to be systematically smaller than measurements from the RHIC and the LHC, an observation that became known as the "direct photon puzzle". I will show that the use of a modern hydrodynamical model of heavy ion collisions and of the latest photon emission rates greatly improves agreement with both ALICE and PHENIX data, supporting the idea that thermal photons are the dominant source of direct photon momentum anisotropy in heavy ion collisions. The eventbyevent hydrodynamical model used includes, for the first time, both shear and bulk viscosities, along with second order couplings between the two viscosities. Calculations using different photon emission rates will be shown, including one that takes into account the effect of confinement on photon emission. The effect of both shear and bulk viscosities on the photon rates will be shown to have a measurable effect on the photon momentum anisotropy.
RIKEN Lunch Seminar
"Walking and conformal dynamics in manyflavor QCD"
Presented by Hiroshi Ohki, RIKEN BNL Research Center
Thursday, October 22, 2015, 12:30 pm
Building 510 Room 2160
Hosted by: Tomomi Ishikawa
We present our lattice results of SU(3) gauge theory with many flavors, in particular with Nf=8, as a model of a walking or conformal gauge theory. We study the scaling properties of various hadron spectra including the (pseudo)scalar, vector, and baryon channels. From the Nf dependence of the theory, possible signals of walking or conformal dynamics will be discussed.
HET/RIKEN Seminar
"Phenomenology of semileptonic Bmeson decays with form factors from lattice QCD"
Presented by Ran Zhou, Fermilab
Wednesday, October 21, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Tomomi Ishikawa
The exclusive semileptonic $B$meson decays $B\to K(\pi)\ell^+\ell^$, $B \to K(\pi)\nu\bar\nu$, and $B\to\pi\tau\nu$ are used to extract the CKM elements and probe new physics beyond Standard Model. The errors of the form factors used to be an important source of the uncertainties in the theoretical predictions. Recent developments in latticeQCD provide more accurate form factors and enable us to have better theoretical predictions. In this talk, I will present the latest latticeQCD results of the form factors in the semileptonic $B$meson decays processes. In addition, I will compare the theoretical predictions and recent experimental results. The tension between the Standard Model and semileptonic $B$meson decay experimental data will be discussed.
RIKEN Lunch Seminar
"pQCD thermodynamics with massive quarks"
Presented by Thorben Graf, Institut fÃ¼r Theoretische Physik, Johann Wolfgang GoetheUniversitÃ¤t
Thursday, October 15, 2015, 12:30 pm
Building 510 Room 2160
Hosted by: Daniel Pitonyak
Results for several thermodynamic quantities within the nexttoleading order calculation of the thermodynamic potential in perturbative QCD at finite temperature and chemical potential including nonvanishing quark masses are presented. These results are compared to lattice data and to higherorder optimized perturbative calculations to investigate the trend brought about by mass corrections. Furthermore, the equation of state for nonvanishing isospin density was investigated within the introduced framework and the findings are also presented.
Nuclear Theory/RIKEN Seminar
"Single inclusive particle production at NLO: revised and improved"
Presented by Alex Kovner, University of Connecticut
Friday, September 18, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
We discuss the recent improvement of the NLO calculation of single inclusive particle production in pA collisions within the CGC formalizm. The two points that have not been addressed previously, and are treated consistently in the current approach are the Ioffe time cutoff on the configurations that can participate in the scattering, and the careful treatment of the evolution interval.
Nuclear Theory/RIKEN Seminar
"Asymptotic freedom of gluons in the Fock space"
Presented by Stanislaw Glazek, University of Warsaw
Friday, September 4, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Asymptotic freedom of gluons is defined in terms of scaledependent renormalized QCD Hamiltonian operators that act in the Fock space. These operators are calculable in a new way [1,2], by solving a doublecommutator differential equation [3], where the derivative is with respect to a scale parameter defined within the renormalization group procedure for effective particles (RGPEP). The RGPEP equation and its solutions are invariant with respect to boosts and may serve as a tool in attempts to dynamically explain the parton and constituent models of hadrons in QCD. The thirdorder QCD solution of the RGPEP equation to be discussed [2], provides an explicit example of how asymptotic freedom of gluons is exhibited in the scaledependence of Hamiltonians as operators in the Fock space. This example also prepares ground for the fourthorder calculations of effective strong interactions using the same RGPEP equation [3], to facilitate Hamiltonian studies of many stronginteraction processes, e.g., those that involve heavy quarkonia in relativistic motion. Applications to other sectors of the Standard Model than the strong interactions await development, while only preliminary results are currently available in the domain of precise calculations in QED[4]. [1] Dynamics of effective gluons, S. D. Glazek, Phys. Rev. D63, 116006, 29p (2001). [2] Asymptotic freedom in the frontform Hamiltonian for gluons, M. GomezRocha, S. D. Glazek, arXiv:1505.06688 [hepph], to appear in Phys. Rev. D. [3] Perturbative formulae for relativistic interactions of effective particles, S. D. Glazek, Acta Phys. Pol. B43, 1843, 20p (2012). [4] Calculation of size for boundstate constituent
RIKEN Lunch Seminar
"Analytic solution of the Boltzmann equation in the early universe"
Presented by Jorge Noronha, University of Sao Paulo
Thursday, September 3, 2015, 12:30 pm
Building 510 Room 2160
Hosted by: Daniel Pitonyak
A general method for exactly computing the nonlinear collision term of the Boltzmann equation for a massless relativistic gas in a homogeneous and isotropic spacetime is presented. This approach is used to find an exact analytical solution of the nonlinear relativistic Boltzmann equation in a FriedmannRobertsonWalker spacetime. This solution can be used to investigate analytically the interplay between global expansion and local thermalization in rapidly evolving systems.
Special Nuclear Theory/RIKEN seminar
"Thermodynamics and topology from lattice QCD"
Presented by Michael MullerPreussker, Humboldt University Berlin
Monday, August 24, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Recent efforts to investigate the thermodynamics of lattice QCD with N_f=2+1+1 fermion degrees of freedom at realistic strange and charm quark masses and at various up and down quark mass values within the framework of Wilson twisted mass fermion discretization are discussed. Comparing with recently published results in the N_f=2 case we are going to present results for the pseudocritical temperature and preliminary results on the way to the thermodynamic equation of state. Moreover, we would like to discuss various methods to determine the topological susceptibility as a function of the temperature.
Nuclear Theory/RIKEN Seminar
"Initial state correlations, entanglement entropy and all that"
Presented by Michal Lublinsky, Ben Gurion University of the Negev
Friday, August 14, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
I will discuss high energy collisions of dilute on dense systems (pA) and review some ideas about initialstate induced correlations.
RIKEN Lunch Seminar
"Discrimination of large quantum ensembles"
Presented by Emilio Bagan, GIQ, Physics Dept., UAB, Spain and Hunter College of the CUNY
Thursday, August 13, 2015, 12:30 pm
Building 510, Room 2160
Hosted by: Daniel Pitonyak
"Hypothesis testing is arguably the most common and elementary task in information processing (e.g., we constantly make decisions based on incomplete information). Its quantum version, quantum state discrimination, is likewise central in quantum information processing. The talk gives an introduction to the topic, focussing on discrimination of a large amount of identically prepared systems. In this limit, a powerful bound on the error rate can be derived. In classical statistics this is know as Chernoff bound. The quantum version of the Chernoff bound will be presented and discussed."
HET/RIKEN seminar
"Higgs coupling deviations, vacuum stability and new bosons at the TeV scale"
Presented by Raffaele D'Agnolo, Institute for Advanced Study
Wednesday, August 5, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: ChienYi Chen
Higgs coupling measurements can shed light on the nature of electroweak symmetry breaking. However it is not trivial to go beyond generic intuitions, such as the expectation that natural theories generate large deviations, and make precise statements. In this talk I will show in a model independent way that measuring deviations at the LHC implies the existence of new bosons between a few TeV and a few hundred TeV. This is true in general, including theories where new fermions produce the deviations.
Nuclear Theory/RIKEN seminar
"Generalized Landaulevel representation for spin1/2 fermions and its applications"
Presented by Igor Shovkovy, Arizona State University
Friday, July 31, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
I will discuss the recently proposed generalized Landaulevel representation for charged fermions in an external magnetic field. After demonstrating its key advantages over the other existing representations, I will mention several of its applications. One of them is the quantum Hall effect in graphene, where the new representation is essential for a sufficiently detailed theoretical description, in which all the dynamical parameters are running functions of the Landaulevel index. The other application is the chiral asymmetry induced in dense relativistic matter in an external magnetic field. The quantitative measure of such an asymmetry is the chiral shift parameter that measures a relative shift of the longitudinal momenta (along the direction of the magnetic field) in the dispersion relations of opposite chirality fermions. Using the language of solid state physics, the corresponding ground state of dense relativistic matter could be interpreted as a Weyl metal state. Incidentally, the exact same mechanism also works in real Dirac metals.
RIKEN Lunch Seminar
"Podd Spectral Density at Weak Coupling: Photon Emission and Second"
Presented by HoUng Yee, University of Illinois at Chicago
Thursday, July 30, 2015, 12:30 pm
Building 510 Room 2160
Hosted by: Daniel Pitonyak
The Podd spectral density of current correlation functions appears in several physical observables which are related to chiral anomaly, and is a sensitive probe of microscopic dynamics which is less protected by symmetry alone. We discuss two examples of their appearance: photon emission and the second order transport coefficient from chiral anomaly. We describe leading order weak coupling computations for these examples.
Nuclear Theory/RIKEN seminar
"Resumming large radiative corrections in the highenergy evolution of the Color Glass Condensate"
Presented by Edmond Iancu, CEA Saclay
Friday, July 24, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Speren Schlichting
The BKJIMWLK equations describing the evolution of the Color Glass Condensate with increasing energy have recently been extended to nexttoleading order (NLO) accuracy. However, some of the NLO corrections turn out to be extremely large, since amplified by (double and single) `collinear' logarithms, i.e. logarithms of ratios of transverse momenta. This difficulty points towards the existence of large radiative corrections to all orders in $\alpha_s$, as generated by the transverse phasespace, which must be computed and resummed in order to restore the convergence of the perturbative expansion. In a couple of recent papers, we developed a resummation scheme in that sense, which achieves a complete resummation of the doublelogarithmic corrections and a partial resummation of the singlelogarithmic ones (including the running coupling effects). We have thus deduced a collinearlyimproved version of the BK equation which includes the largest radiative corrections to all orders. To demonstrate the usefulness of this equation as a tool for phenomenology, for have used it for fits to the HERA data for electronproton deep inelastic scattering at high energy. We have obtained excellent fits with a reduced number of free parameters and with initial conditions at low energy taken from perturbative QCD.
Nuclear Theory/RIKEN seminar
"The LPM effect in energy loss and sequential bremsstrahlung"
Presented by Peter Arnold, University of Virginia
Friday, July 17, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Highenergy particles passing through matter lose energy by showering via hard bremsstrahlung and pair production. At very high energy, the quantum duration of each splitting process, known as the formation time, exceeds the mean free time for collisions with the medium, leading to a significant reduction in the splitting rate, known as the LandauPomeranchukMigdal (LPM) effect. A longstanding problem in field theory has been to understand how to implement this effect in cases where the formation times of two consecutive splittings overlap. I will review why this question is interesting and discuss recent progress in the context of jet energy loss in quarkgluon plasmas.
Nuclear Theory/RIKEN Seminar
"Event by Event fluctuations in pQCD + saturation + hydro model: pinning down QCD matter shear viscosity in AA collisions"
Presented by Risto Paatelainen, University of Jyvaskyla
Friday, June 26, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
We introduce an eventbyevent perturbativeQCD + saturation + hydro ("EKRT") framework for ultrarelativistic heavyion collisions, where we compute the produced fluctuating QCDmatter energy densities from nexttoleading order perturbative QCD using a saturation conjecture to control soft particle production, and describe the spacetime evolution of the QCD matter with dissipative fluid dynamics, event by event. We perform a simultaneous comparison of the centrality dependence of hadronic multiplicities, transverse momentum spectra, and flow coefficients of the azimuthangle asymmetries, against the LHC and RHIC measurements. We compare also the computed eventbyevent probability distributions of relative fluctuations of elliptic flow, and eventplane angle correlations, with the experimental data from Pb+Pb collisions at the LHC. We show how such a systematic multienergy and multiobservable analysis tests the initial state calculation and the applicability region of hydrodynamics, and in particular how it constrains the temperature dependence of the shear viscositytoentropy ratio of QCD matter in its different phases in a remarkably consistent manner.
RIKEN Lunch Seminar
"OneFlavor QCD and the Dirac Spectrum at $\theta=0$"
Presented by Jacobus Verbaarschot, Stony Brook University
Thursday, June 25, 2015, 12:30 pm
Building 510 Room 2160
Hosted by: Daniel Pitonyak
The chiral condensate of oneflavor QCD is continuous when the quark mass crosses zero. In the sector of fixed topological charge though, the chiral condensate becomes discontinuous at zero mass in the the thermodynamical limit. To reconcile these contradictory observations, we have evaluated the spectral density of the Dirac operator in the epsilon domain of oneflavor QCD. In this domain, we have obtained exact analytical expressions which show that the spectral density at $\theta = 0$ becomes a strongly oscillating function for negative quark mass with an amplitude that increases exponentially with the volume. As is the case for QCD at nonzero chemical potential, these strong oscillations invalidate the BanksCasher formula and result in a chiral condensate that is continuous as a function of the quark mass. An additional subtlety is the effect of the topological zero modes which will be discussed as well.
Nuclear Theory/RIKEN seminar
"Jet angular broadening in HeavyIon collisions"
Presented by Yacine MehtarTani, University of Washington
Friday, June 19, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
The advent of the LHC opened up new perspectives for jetquenching physics. For the first time, high enough energies are reached in heavyion experiments to produced jets in large numbers, and the unprecedented detector capabilities of ALICE, ATLAS and CMS, not only extend the kinematic range for the measurements previously performed at RHIC, but also allow to explore a variety of new jetquenching observables. In this talk, I address the question of the angular broadening of jets in the presence of a dense QCD matter. I start by discussing the fundamental mechanisms underlying the formation of gluon cascades induced by multiple interactions of high energy jets with the quarkgluon plasma. Then, the rate equation that describes the evolution of the energy and angular distribution of the inmedium gluon shower is presented and solved. Two remarkable phenomena emerge. First and foremost the energy spectrum (of jet constituents) exhibits a scaling behavior characterized by a constant flow of energy towards low momenta akin to wave turbulence. As a result, energy is rapidly transported from the energy containing partons to low momentum gluons before it dissipates into the medium. Second, mediuminduced gluon cascades develop and transport energy at parametrically large angles with respect to the jet axis. This picture is in semiquantitive agreement with a recent CMS analysis of the missing energy in asymmetric dijet events where the energy balance is recovered at large angles and very soft particles.
RIKEN Lunch Seminar
"Selfsimilar evolution for inverse cascade of magnetic helicity driven by the chiral anomaly"
Presented by Yi Yin, Brookhaven National Laboratory
Thursday, June 18, 2015, 12:30 pm
Small Seminar Room, Bldg. 510
Hosted by: Daniel Pitonyak
We show by solving Maxwell's equations in the presence of chiral magnetic current that the chiral anomaly would induce the inverse cascade of magnetic helicity. We found at late time, the evolution of magnetic helicity spectrum is selfsimilar and axial charge decays as a power law in time. We visualize how a linked magnetic configuration would evolve into a knotted configuration in real space during such evolution.
HET/RIKEN seminar
"New physics in b—>s transitions after LHC run 1"
Presented by Wolfgang Altmannshofer, Perimeter Institute
Wednesday, June 10, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: ChienYi Chen
I will discuss interpretations of the recent updated angular analysis of the B>K*mu+mu decay by the LHCb collaboration. A global fit to all relevant measurements probing the flavor changing neutral current b>s mu mu transition shows tensions with Standard Model expectations. Assuming hadronic uncertainties are estimated in a sufficiently conservative way, I will discuss the implications of the experimental results on new physics, both model independently as well as in the context of models with flavor changing Z' bosons.
Nuclear Theory/RIKEN seminar
"Novel mechanisms of charmonium suppression/enhancement in pA and AA collisions"
Presented by Boris Kopeliovich, Universidad Tecnica Federico Santa Maria, Valparaiso
Friday, June 5, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Charmonium production in pA collisions is known to be suppressed by shadowing and absorption. There are however nuclear effects, which enhance charmonium yield. They steeply rise with energy and seem to show up in LHC data for J/psi production in pA collisions. In the case of heavy ion collisions produced charmonia are additionally suppressed by final state interaction in the created dense medium. On the contrary to current evaluations of the melting effects caused by Debye screening, a charmonium produced with a large pT easily survives even at high temperatures. Another source of charmonium suppression, missed in previous calculations, colorexchange interactions with the medium, leads to suppression of a comparable magnitude. A quantitative comparison is performed.
RIKEN Lunch Seminar
"Dysonian dynamics of the Ginibre ensemble"
Presented by Piotr Warchol, Jagiellonian University
Thursday, May 21, 2015, 12:30 pm
Building 510 Room 2160
Hosted by: Tomomi Ishikawa
I will present a study of the time evolution of Ginibre matrices whose elements undergo Brownian motion. The nonHermitian character of the Ginibre ensemble binds the dynamics of eigenvalues to the evolution of eigenvectors in a nontrivial way, leading to a system of coupled nonlinear equations resembling those for turbulent systems. We will formulate a mathematical framework allowing simultaneous description of the flow of eigenvalues and eigenvectors, and unravel a hidden dynamics as a function of new complex variable, which in the standard description is treated as a regulator only. We shall solve the evolution equations for large matrices and demonstrate that the nonanalytic behavior of the Green's functions is associated with a shock wave stemming from a Burgerslike equation describing correlations of eigenvectors. I will start by reviewing similar notions in a simpler, Hermitian setting. Joint work with Zdzislaw Burda, Jacek Grela, Maciej A. Nowak and Wojtek Tarnowski (Phys.Rev.Lett. 113 (2014) 104102).
RIKEN Lunch Seminar
"Geometrical scaling  a window to saturation"
Presented by Michal Praszalowicz, Jagiellonian University
Thursday, May 14, 2015, 12:30 pm
Building 510 Room 2160
Hosted by: Daniel Pitonyak
Geometrical is a consequence of a traveling wave solution of the nonlinear QCD evolution equation, so called BalitskiKovchegov equation. We shall demonstrate the existence of GS in various high energy reactions. Among different consequences of GS there is a linear rise of charged particle multiplicity (Nch) and mean transverse momentum (pT) with scattering energy. Furthermore, a correlation of meant pT and Nch is predicted to scale in a way that depends on the the way particles are produced from the volume excited in a hadronhadron scattering. This is mostly visible in heavy ion collisions at different centralities.
Nuclear Theory/RIKEN Seminar
"Solving the NLO BK equation in coordinate space"
Presented by Tuomas Lappi, University of Jyvaskyla
Friday, May 8, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
We present results from a numerical solution of the nexttoleading order (NLO) BalitskyKovchegov (BK) equation in coordinate space in the large Nc limit. We show that the solution is not stable for initial conditions that are close to those used in phenomenological applications of the leading order equation. We identify the problematic terms in the NLO kernel as being related to large logarithms of a small parent dipole size, and also show that rewriting the equation in terms of the "conformal dipole" does not remove the problem. Our results qualitatively agree with expectations based on the behavior of the linear BFKL equation.
Nuclear Theory/RIKEN Seminar
"Applications of SoftCollinear Effective theory to hadronic and nuclear collisions"
Presented by Ivan Vitev, Los Alamos National Laboratory
Friday, May 1, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Effective field theory (EFT) is a powerful framework based on exploiting symmetries and controlled expansions for problems with a natural separation of energy or distance scales. EFTs are particularly important in QCD and nuclear physics. An effective theory of QCD, ideally suited to jet applications, is SoftCollinear Effective Theory (SCET). Recently, first steps were taken to extend SCET and describe jet evolution in stronglyinteracting matter. In this talk I will demonstrate that the newly constructed theory, called SCETG, allows us to go beyond the traditional energy loss approximation in heavy ion collisions and unify the treatment of vacuum and mediuminduced parton showers. It provides quantitative control over the uncertainties associated with the implementation of the inmedim modification of hadron production cross sections and allows us to accurately constrain the coupling between the jet and the medium. I will further show how SCET and SCETG can be implemented to evaluate reconstructed jet observables, such as jet shapes.
Nuclear Theory/RIKEN seminar
"Heavy Hadrons under Extreme Conditions"
Presented by Laura Tolos, Instituto de Ciencias del Espacio (IEECCSIC)
Friday, April 24, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Hadrons under extreme conditions of density and temperature have captured the interest of particle and nuclear physicists as well as astrophysicists over the years in connection with an extensive variety of physical phenomena in the laboratory as well as in the interior of stellar objects, such as neutron stars. One of the physics goals is to understand the origin of hadron masses in the context of the spontaneous breaking of the chiral symmetry of Quantum Chromodynamics (QCD) at low energies in the nonperturbative regime and to analyze the change of the hadron masses due to partial restoration of this symmetry under extreme conditions. Lately other proper QCD symmetries have also become a matter of high interest, such as heavyquark flavor and spin symmetries. These symmetries appear when the quark masses become larger than the typical confinement scale and they are crucial for characterizing hadrons with heavy degrees of freedom. In this talk I will address the properties of heavy hadrons under extreme conditions based on effective theories that incorporate the most appropriate scales and symmetries of QCD in each case. With the ongoing and upcoming research facilities, the aim is to move from the lightquark to the heavyquark sector and to face new challenges where heavy hadrons and new QCD symmetries will play a dominant role.
Nuclear Physics & RIKEN Theory Seminar
"Consistency of Perfect Fluidity and Jet Quenching in semiQuarkGluon Monopole Plasmas"
Presented by Jiechen Xu, Columbia University
Friday, April 17, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Abstract: We utilize a new framework, CUJET3.0, to deduce the energy and temperature dependence of jet transport parameter, q^(E>10GeV,T), from a combined analysis of available data on nuclear modification factor and azimuthal asymmetries from RHIC/BNL and LHC/CERN on high energy nuclear collisions. Extending a previous perturbativeQCD based jet energy loss model (known as CUJET2.0) with (2+1)D viscous hydrodynamic bulk evolution, this new framework includes three novel features of nonperturbative physics origin: (1) the Polyakov loop suppression of colorelectric scattering (aka "semiQGP" of Pisarski et al) and (2) the enhancement of jet scattering due to emergent magnetic monopoles near Tc (aka "magnetic scenario" of Liao and Shuryak) and (3) thermodynamic properties constrained by lattice QCD data. CUJET3.0 reduces to v2.0 at high temperatures T>400 MeV, but greatly enhances q^ near the QCD deconfinement transition temperature range. This enhancement accounts well for the observed elliptic harmonics of jets with pT>10 GeV. Extrapolating our dataconstrained q^ down to thermal energy scales, Eâˆ¼2 GeV, we find for the first time a remarkable consistency between high energy jet quenching and bulk perfect fluidity with Î·/sâˆ¼T3/q^âˆ¼0.1 near Tc.
Nuclear Theory/RIKEN seminar
"Hydrodynamics Beyond the Gradient Expansion: Resurgence and Resummation"
Presented by Michael Heller, Perimeter Institute
Friday, April 10, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Consistent formulations of relativistic viscous hydrodynamics involve short lived modes, leading to asymptotic rather than convergent gradient expansions. In this talk I will consider the MuellerIsraelStewart theory applied to a longitudinally expanding quarkgluon plasma system and identify hydrodynamics as a universal attractor without invoking the gradient expansion. I will give strong evidence for the existence of this attractor and then show that it can be recovered from the divergent gradient expansion by Borel summation. This requires careful accounting for the shortlived modes which leads to an intricate mathematical structure known from the theory of resurgence.
Nuclear Theory/RIKEN seminar
"Gravitational collapse, holography and hydrodynamics in extreme conditions"
Presented by Paul Chesler, Harvard University
Friday, April 3, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
A remarkable observation from RHIC and the LHC is that the quarkgluon plasma produced in heavyion collisions behaves as a strongly coupled and nearly ideal liquid. Data also suggests that the debris produced by protonnucleus collisions can also behave as a liquid. Understanding the dynamics responsible for the rapid equilibration of such tiny droplets is an outstanding problem. In recent years holography has emerged as a powerful tool to study nonequilibrium phenomena, mapping challenging quantum dynamics onto the classical dynamics of gravitational fields in one higher dimension. In the dual gravitational description the process of quarkgluon plasma formation and equilibration maps onto the process of gravitational collapse and black hole formation. I will describe how one can apply techniques and lessons learned from numerical relativity to holography and present recent work on holographic models of high energy collisions and the applicability of hydrodynamics to tiny droplets of quarkgluon plasma.
RIKEN Lunch Seminar
"SpinOrbit Coupling in an Unpolarized Heavy Nucleus"
Presented by Matt Sievert, BNL
Thursday, April 2, 2015, 12:30 pm
Building 510 Room 2160
Hosted by: Daniel Pitonyak
The nextgeneration ElectronIon Collider (EIC) will make high precision measurements of spindependent observables at high energies on nuclear targets. This unique nuclear physics laboratory will bring together access to the multitude of spinspin and spinorbit structures which can exist in hadronic targets, and the high colorcharge densities which generate the most intense gluon fields permitted by quantum mechanics. The interplay between those two features gives rise to new physical mechanisms which translate these spinorbit structures into the observed crosssections, and it makes these mechanisms amenable to firstprinciples calculation. In this talk, I will discuss the spinorbit structure of quarks within an unpolarized heavy nucleus in the quasiclassical approximation. The possibility of polarized nucleons with orbital motion inside the unpolarized nucleus generates nontrivial mixing between the spinorbit structures of the nucleons, and the corresponding structures in the nucleus. This generic feature of a dense quasiclassical system leads to direct predictions testable at an EIC, and in principle allows direct access to the orbital angular momentum in the nucleus.
HET/RIKEN seminar
"Flavored Dark Matter with Weak Scale Mediators"
Presented by Can Kilic, The University of Texas, Austin
Wednesday, March 25, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: ChienYi Chen
All matter in the Standard Model appears in three generations, with an intricate flavor structure the origin of which is not well understood. This motivates the question whether distinct phenomenological features arise if dark matter (DM) also has a nontrivial flavor structure. In this talk I will review the experimental signatures of this scenario. In the case of leptonflavored DM, I will argue that the generation of a lepton asymmetry at a high energy scale can also produce a DM asymmetry, which can strongly affect the sensitivity of direct detection experiments, and I will present novel signatures that can appear at colliders and in indirect detection experiments. I will also review the case of top quarkflavored DM with a distinct collider phenomenology including final states of top pairs and missing energy as well the possibility of displaced decays.
Joint NT/RIKEN Seminar
"Flowlike behavior in small systems — Multiparton interactions and color reconnection effects at the LHC"
Presented by Antonio Ortiz Velasquez, National Autonomous University of Mexico
Friday, March 20, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Soeren Schlichting
Collectivity in high multiplicity pp and pPb collisions is the most unexpected discovery at the LHC, its origin is still an open question. In heavy ion collisions, collectivity is attributed to final state effects due to the presence of a hot and dense QCD medium, and it is well described by viscous hydrodynamical calculations with fluctuating initial state geometries. Surprisingly, calculations which employ hydrodynamics reproduce qualitatively well the features of pPb data, but, the applicability of hydro in small systems faces conceptual problems. This is not the case of other approaches which do not require a medium to be formed and also are able to reproduce qualitatively well some features of data. In this talk it will be shown that multiparton interactions and color reconnection (CR) produce flowlike effects in high multiplicity pp collisions. A study of the transverse momentum (pT) distribution of identified hadrons as a function of the event multiplicity will be presented. This comprises studies of the average pT vs hadron mass and number of constituent quarks, and a pT differential study using the BoltzmannGibbs BlastWave model. A comparison between hydro and color reconnection calculations will be presented. In this context, the results from the same study using LHC data (pp, pPb and PbPb collisions) will be discussed.
RIKEN BNL
"The title of my talk is "How Jets and TwoParticle Correlations Impact Our Understanding of the Quark Gluon Plasma"
Presented by Megan Connors, Yale University
Wednesday, March 18, 2015, 2 pm
Building 510 Room 2160
Hosted by: Samuel Aronson
Relativistic heavy ion collisions can reproduce the conditions necessary to form a hot and dense medium known as the Quark Gluon Plasma (QGP), the state of the universe immediately following the Big Bang, in which quarks and gluons are deconfined. Results from experiments at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC), which study the properties of the QGP, will be presented. This seminar will focus on two particle correlations and jet physics results in PbPb and AuAu collisions at the LHC and RHIC respectively and the prospects for such measurements at the proposed sPHENIX detector. In addition, the implications of using pp or pA systems as a reference for these AA measurements will be discussed. Jets are the result of a hard scattering, which occurs early in the collision process, and probe how partons interact and lose energy in the medium. Two particle correlations are used to study jet physics and energy loss, as well as the underlying event. The interplay between the two is important for understanding how high momentum particles lose energy and for finding where that lost energy goes. To quantify the influence of the QGP on these measurements, it is important to have a good baseline measurement. AA measurements are typically compared to expectations based on pp collisions. Recent results from pA collisions are used to quantify cold nuclear matter effects not captured in pp collisions. However, pA measurements have proven to be interesting in their own unexpected way which has implications for physics measurements at the future Electron Ion Collider.
RIKEN/BNL Lunch Time Talk
"BoseEinstein Condensation, Isotropization, and Thermalization in Overpopulated Systems"
Presented by Jinfeng Liao, Indiana University / RBRC
Thursday, February 12, 2015, 12:30 pm
Building 510 Room 2160
Hosted by: Tomomi Ishikawa
We discuss recent progress, using the kinetic theory framework, in understanding the nonequilibrium evolution of overpopulated systems that resemble the glasma during the early stage of heavy ion collisions. We analyze a number of important factors that influence the course of thermalization in such systems, and in particular their consequences for the nontrivial dynamics driving BoseEinstein Condensation as well as the isotropization. We discuss recent progress, using the kinetic theory framework, in understanding the nonequilibrium evolution of overpopulated systems that resemble the glasma during the early stage of heavy ion collisions. We analyze a number of important factors that influence the course of thermalization in such systems, and in particular their consequences for the nontrivial dynamics driving BoseEinstein Condensation as well as the isotropization.
HighEnergy Physics & RIKEN Theory Seminar
"Electric Dipole Moments, New Physics, and (lattice) QCD"
Presented by Vincenzo Cirigliano, Los Alamos
Wednesday, February 11, 2015, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Sally Dawson
In this talk I will discuss the role of electric dipole moments (EDMs) as probes of physics beyond the Standard Model (BSM). In the first part of the talk I will present an overview of the physics reach of various searches and I will discuss the complementarity of different EDM probes. In the second part of the talk I will discuss ongoing work towards the computation of the BSMinduced neutron and proton EDM using lattice Quantum ChromoDynamics.
RIKEN/BNL Lunch Time Talk
"The Higgs boson mass  what does it mean for the Standard Model?"
Presented by Fedor Bezrukov, University of Connecticut/RBRC
Thursday, August 16, 2012, 12:30 pm
Building 510 / Room 2160
Hosted by: Tomomi Ishikawa
The Higgs boson with the mass recently announced by the LHC experiments corresponds within current precision to the boundary value between the situations when the electroweak vacuum is stable and metastable. I will discuss the latest developments in the calculation of this boundary mass and importance of measurement of other SM parameters (top quark mass and the strong coupling constant). I will also discuss what is the meaning of this boundary value in various minimal modifications of the Standard Model.
Nuclear Physics & RIKEN Theory Seminar
"The azimuthal anisotropy of high P_t hadrons in RHIC and LHC"
Presented by Xilin Zhang, Indiana University
Friday, July 27, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
In this talk, I will present our study on the azimuthal anisotropy of high p_t particles (from jets) in the relativistic heavy ion collisions, which encode the information about jet energy loss in the medium as well as the medium itself. We focus on three different models with distinctive pathlength and matterdensity dependence of the energy loss: L^{2}, L^{3}, and nearTcenhancement (NTcE). We will first show our simple estimate of jet response to the shape fluctuation of the medium (initial state fluctuation) in the central 200 AGeV AuAu collision. Second, the MC Glauber model is applied to study different Fourierharmonics (V_{1,2,3,,,6}) of the final high P_t hadron spectrum in the noncentral collisions at both RHIC and LHC (PbPb collision). We find both L^{3} and NTcE can explain V_2 at RHIC (L^{2} underestimates it by roughly 20%), while L^{2} and NTcE are successful at LHC@2.76 TeV (L^{3} overestimates it by roughly 20%). In addition, we see the consistency between our NTcE calculations for other higher harmonics and the LHC@2.76 TeV data. The predictions of these harmonics for LHC@5.5 TeV will also be presented.
Nuclear Physics & RIKEN Theory Seminar
"Hydrodynamics at large baryon densities: Understanding proton vs. antiproton $v_2$ and other puzzles"
Presented by Jan SteinheimerFroschauer, University of Frankfurt/Lawrence Berkeley National Laboratory
Friday, July 20, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Adam Bzdak
Using hydrodynamics we explore the effects of the initial state, baryon stopping and baryon number transport on various observables such as spectra, elliptic flow and particle yields for heavy ion collisions at beam energies from $\sqrt{s_{NN}}=7.7$ to $200$ GeV. In our setup the transition from the equilibrated hydrodynamical phase to the final transport phase occurs over a broad range of temperatures/densities. Even though particle yields, extracted at this transition, can be described well by a single temperature freeze out we observe a correlation of particle mass, average transition temperature and flow velocity which allows us to successfully describe the measured nonmonotonic behavior of the effective slope parameter as a function of particle mass. Furthermore we show that observed phenomena such as the centrality dependent freeze out parameters as well the asymmetry in particle/antiparticle $v_2$ at large baryon densities can be explained by a collective hydrodynamic expansion, once baryon stopping and baryon number conservation are properly taken into account. We will further discuss how the various stages of the collision contribute to the $p_{\bot}$ spectra and the mass dependence of $T_{eff}$.
Nuclear Physics & RIKEN Theory Seminar
"More on the string inspired solution to the sign problem and overlapping problem"
Presented by Masanori Hanada, KEK Theory Center
Friday, July 13, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
The effect of the complex phase of the fermion determinant is a key question related to the sign problem in finitedensity QCD. Recently, based on a fieldtheoretic argument inspired by the string theory, it has been shown that ignoring the complex phase  the phase quenching  does not change the expectation values of a class of observables in a certain region of the phase diagram when a number of colors Nc is large. In this talk we briefly explain this equivalence and show that the same equivalence holds in effective models and holographic models. We show, in a unified manner, that the phase quenching gives exact results for a class of fermionic observables (e.g., chiral condensate) in the meanfield approximation and for gaugeinvariant gluonic observables (e.g., Polyakov loop) up to onemesonloop corrections beyond mean field. We also discuss implications for the lattice simulations and confirm good quantitative agreement between our prediction and existing lattice QCD results. Therefore the phase quenching provides rather accurate answer already at Nc=3 with small 1/Nc corrections which can be taken into account by the phase reweighting.
RIKEN/BNL Lunch Time Talk
"Evolution of singularities in unequal time correlator in thermalization of strongly coupled gauge theory"
Presented by Shu Lin, RBRC
Thursday, July 12, 2012, 12:30 pm
Building, 510/Room 2160
Hosted by: Tomomi Ishikawa
Thermalization of strongly coupled gauge theory can be described by a gravitational collapse process via gauge/gravity duality. We studied the evolution of unequal time correlator in a gravitational collapse background, which allowed us to probe different stages of thermalization process. We found that the singularities of the correlator are consistent with geometric optics picture in the gravitational collapse background. We found the thermalization is characterized by the disappearance of singularities on real time axis and possible emergence of singularities in complex time plane in the correlator.
Nuclear Physics & RIKEN Theory Seminar
"Quark superfluidity in the twofluid formalism"
Presented by Andreas Schmitt, Vienna Technical University
Friday, June 29, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
Various observables of neutron stars depend on hydrodynamic properties of the matter inside the star. This matter is likely to be a superfluid, for instance in the colorflavor locked (CFL) phase of quark matter. I will discuss the nontrivial superfluid properties of CFL and, in particular, present a "translation" between microscopic, fieldtheoretical calculations and the twofluid picture of a relativistic superfluid.
Nuclear Physics & RIKEN Theory Seminar
"Putting a Saturation Spin on Transverse Spin Asymmetries"
Presented by Matt Sievert, Ohio State University
Friday, June 22, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
In hadron collisions, the single transverse spin asymmetry (STSA) is an observable describing the leftright asymmetry in the spectrum of produced particles when one of the colliding hadrons is polarized transverse to the beam axis. Since the discovery of unexpectedly large STSA's at the Tevatron in the 1990's, these spin asymmetries have consistently challenged accepted paradigms in factorization, universality, and perturbative QCD. Current theoretical treatments describe the generation of asymmetry in two nonperturbative sectors: the intrinsic parton distribution functions (Sivers effect) and the fragmentation functions (Collins effect). In this talk, I will discuss how the systematic enhancement of certain scattering processes for high energies or large nuclei (saturation formalism) leads to an asymmetry that can be generated at the perturbative level. Our new mechanism generates the STSA through a Codd scattering process known as the “odderon,” a hypothetical interaction originating from the field of Regge physics. I will present our general result deriving the new mechanism and some numerical estimates illustrating its features. I will conclude by describing some of the scaling properties of our mechanism and illustrating its essential features.
RIKEN/BNL Lunch Time Talk
"Nucleon structure from 2+1flavor dynamical DWF QCD at nearly physical pion mass"
Presented by Shigemi Ohta, KEK/RBRC
Thursday, June 7, 2012, 12:30 pm
Building 510 / Room 2160
Hosted by: Tomomi Ishikawa
I report the current status of joint RBC+UKQCD numerical lattice QCD study of nucleon structure using several 2+1flavor dynamical domainwall fermions (DWF) ensembles with pion mass as low as 170 MeV and spatial volume as large as \(L=4.6\) fm across. Isovector form factors of vector and axialvector currents and some low moments of isovector structure functions will be discussed. In particular the results for the ratio of vector and axial charges, gA/gV, calculated at pion mass of about \(m_\pi=250\) MeV seems to confirm our earlier conjecture that the quantity scales with a parameter \(m_\pi L\).
Nuclear Physics & RIKEN Theory Seminar
"Aspects of the nonequilibrium dynamics of relativistic heavy ion collisions"
Presented by Soeren Schlichting, University of Heidelberg
Friday, May 25, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
The nonequilbrium dynamics of relativistic heavy ion collisions provides one of the key challenges in our current understanding of the experiments carried out at RHIC and the LHC. In this talk I will discuss the evolution of the 'Glasma' created immediately after the collision of heavy nuclei. I will discuss the different dynamical stages which arise in this context and are characterized by the rapid growth of quantum fluctuations due to nonequilbirum instabilities, the onset of nonlinear effects and ultimately the approach to thermal equilibrium. Both numerical and analytical considerations will be presented.
RIKEN/BNL Lunch Time Talk
"Electroweak Axions, Instantons and the Cosmological Constant"
Presented by Larry McLerran, Brookhaven National Laboratory
Thursday, May 3, 2012, 12:30 pm
Building 510 / Room 2160
Hosted by: Tomomi Ishikawa
I argue that in electroweak theory, an electroweak axion has the right energy density to correspond to the dark energy. This electroweak axion is the Goldstone boson of B+L symmetry, in the absence of instantons. Instantons generate an axion mass. The resulting axion has a mass of the order the inverse size of the universe. The dark energy is associated with the axion field energy. This result assumes no new physics up to of order the Planck scale.
Nuclear Physics & RIKEN Theory Seminar
"Scattering from N=4 to N=0"
Presented by Simon CaronHuot, IAS Princeton
Friday, April 27, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
I will discuss the simplicity found empirically for gluon scattering amplitudes in planar N=4 super YangMills over the past few years, and argue that its origin is now fully understood. The amplitudes are governed by symmetries, and can be computed using them. I will then discuss how this leads to striking facts about individual Feynman integrals, which remain true beyond N=4 and can be applied to QCD.
Joint HET/RIKEN/YITP Seminar
"A novel phase in SU(3) gauge theory with many light fermions"
Presented by Anna Hasenfratz, University of Colorado at Boulder
Wednesday, April 18, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Christoph Lehner
In this talk I will discuss the results of our recent study of the phase structure of SU(3) lattice gauge theory with $N_f = 12$ and 8 staggered fermions in the fundamental representation. For small fermion masses we found two bulk phase transitions at strong gauge couplings. The phase between the two transitions appears to be a novel phase that breaks the single site shift symmetry of staggered fermions. The eigenvalue spectrum of the Dirac operator, the static potential and the meson spectrum collectively establish that this novel phase is confining but chirally symmetric. The phase is bordered by firstorder phase transitions, and since we find the same phase structure with $N_f = 8$ fermions, it is most likely that this novel phase is a strongcoupling lattice artifact, the existence of which does not imply IR conformality. (ArXiv:1111:2317)
Nuclear Physics & RIKEN Theory Seminar
"Understanding the noise in lattice calculations"
Presented by Amy Nicholson, University of Maryland
Friday, April 13, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
Learning about the QCD phase diagram at low temperatures using lattice QCD has proven highly difficult due to the wellknown sign problem, which manifests itself as a noise problem in canonical formalisms. In this talk, I will show that noise in lattice calculations tends to fall into two classes, corresponding to symmetric and longtailed distributions, respectively, based on the physics of the system under study. I will present a lattice study of unitary fermions, a simplified system which we can use to understand the noise problem for longtailed distributions, and show that understanding the distribution allows us to both tame the noise problem and extract previously unknown physical results for systems of bosons at unitarity, known as Efimov states, from the distribution itself. Finally, I will discuss the possible applicability of these findings to lattice QCD calculations.
Nuclear Physics & RIKEN Theory Seminar
"Recent results from chiral effective models"
Presented by Dirk Rischke, J.W. Goethe University, Frankfurt, Germany
Friday, April 6, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Rob Pisarski
In this talk, I present results from an effective model based on the linear representation of the chiral U(N_f)_r x U(N_f)_l symmetry of QCD. It is demonstrated that a reasonable fit of the mass parameters and coupling constants of the model to hadron vacuum properties is possible. This fit can contribute to answering the question about the quark content of the scalar isoscalar mesons. The ultimate goal is to use this model to investigate signatures for chiral symmetry restoration at nonzero temperatures and densities.
HighEnergy Physics & RIKEN Theory Seminar
"Parity violation constraints on top physics"
Presented by Sean Tulin, Michigan Center for Theoretical Physics
Wednesday, April 4, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Elisabetta Furlan
An excess top forwardbackward asymmetry has been measured by the CDF and D0 collaborations, motivating many new physics theories beyond the Standard Model and searches for toprelated anomalies at the LHC. I discuss the implications of lowenergy precision tests of parity violation (PV) on these new physics models, and in fact many of the most promising scenarios are actually ruled out by current PV constraints.
Nuclear Physics & RIKEN Theory Seminar
"Heavy Flavor in Hot/Dense Matter"
Presented by Ralf Rapp, Texas A&M
Friday, March 23, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
Heavy quarks (charm and bottom) provide a versatile tool to study properties of the QuarkGluon Plasma (QGP) and their manifestation in ultrarelativistic heavyion collisions. The large quark mass offers unique opportunities for theoretical control over basic inmedium quantities. We will discuss how a potentialbased Tmatrix approach can be used to comprehensively evaluate both quarkonium boundstate properties and heavyflavor transport in the medium. Constraints from vacuum spectroscopy, perturbative QCD and thermal latticeQCD are applied to enhance the reliability of the calculations. The heavylight quark Tmatrices in the QGP lead to resonance formation close to Tc which naturally lead to coalescence mechanisms for hadronization. Pertinent Langevin simulations of heavyflavor transport through QGP, hadronization and the hadronic phase are implemented into a hydrodynamic evolution to arrive at a uniform strongcoupling treatment of both micro and macrophysics in heavyflavor observables.
Nuclear Physics & RIKEN Theory Seminar
"Dihadron angular correlations in Color Glass Condensate formalism: multigluon correlators"
Presented by Jamal JalilianMarian, Baruch College
Friday, March 16, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
Dihadron angular correlations in the forward rapidity region of protonnucleus collisions probe multigluon correlators (npoint functions of Wilson lines) in the wave function of target nucleus at small x and thus, provide a more detailed picture of QCD dynamics at high energy (CGC). The Renormalization Group equations that govern the energy dependence of these npoint functions will be derived and their approximate solutions motivated. A connection to an alternative approach to high energy QCD, based on BJKP equation involving pomeron and Reggeon exchanges, will be made.
Nuclear Physics & RIKEN Theory Seminar
"Thermal production of relativistic righthanded neutrinos"
Presented by Dietrich Bodeker, Universitaet Bielefeld
Wednesday, March 14, 2012, 11 am
Small Seminar Room, Bldg. 510
Hosted by: Bjoern P. Schenke
The production of righthanded neutrinos is important for models of baryogenesis through leptogenesis. Relativistic righthanded neutrinos are produced through 2 > 2 scattering and nearly collinear 1 <> 2 emission which involves multiple scattering mediated by soft gauge bosons. I discuss the complete leading order calculation of the production rate.
RIKEN/BNL Lunch Time Talk
"Baryon number probability distribution near a phase transition"
Presented by Kenji Morita, YITP, Kyoto University
Thursday, March 8, 2012, 12:30 pm
Building 510 / Room 2160
Hosted by: Zhongbo Kang
I discuss the baryon number probability distribution at finite temperature and chemical potential. Starting from a model thermodynamic potential which has divergent kurtosis at the phase transition, I show how to calculate the probability distribution and its relation to the analytic structure of the thermodynamic potential at complex chemical potential.
HighEnergy Physics & RIKEN Theory Seminar
"Constraining Dark Matter"
Presented by Haibo Yu, University of Michigan
Wednesday, March 7, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Yingchuan Li
Astrophysical and cosmological observations provide compelling evidence for the existence of dark matter in the universe, but its particle physics nature remains mysterious. In this talk, I will discuss how hardron colliders and neutron stars can help us understand dark matter properties. Using an effective field theory approach, we show that monojet+missing energy searches at the Tevatron and LHC can provide a probe of dark matter, which is complementary to direct detection experiments, and in some cases the colliders provide an even stronger constraint. Stellar systems are natural laboratories for exploring dark matter. We show dark matter particles accumulated in old neutron stars can form mini black holes and lead to the destruction of host stars. The observation of old neutron stars actually excludes a class of dark matter models.
Nuclear Physics & RIKEN Theory Seminar
"Hydrodynamic Fluctuations in Relativistic Heavy Ion Collisions"
Presented by Berndt Mueller, Duke University
Friday, March 2, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
The success of relativistic hydrodynamics in describing the fireball created in ultrarelativistic heavy ion collisions opened the possibility to study the properties of strongly interacting matter at extremely high temperatures and densities near thermal equilibrium. A remarkably small value of the shear viscosity near the unitary limit has been deduced from comparison of the results of relativistic viscous fluid dynamics simulations with data from Au+Au collisions at the Relativistic Heavy Ion Collider (RHIC). Due to the fluctuationdissipation theorem, the shear and bulk viscosities not only control the dissipative properties of a fluid in the limit of small velocity gradients, but they also control the magnitude of hydrodynamic fluctuations in the fluid. In my talk, I will explain the relativistic theory of hydrodynamical fluctuations in general and show how it can be applied to the evolution of the quarkgluon plasma formed in relativistic heavyion collisions. As an example, I will present the semianalytic solution of the equations of hydrodynamic fluctuations around the boost invariant Bjorken flow and discuss the structure of the correlation function of particle multiplicity correlations in rapidity space.
Nuclear Physics & RIKEN Theory Seminar
"Deeply Virtual Compton Scattering at a proposed highluminosity ElectronIonCollider"
Presented by Dieter Mueller, Brookhaven National Laboratory
Friday, February 24, 2012, 11 am
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
We study deeply virtual Compton scattering at a proposed electronioncollider and explore the possible impact of such measurements for the access of generalized parton distributions. In particular we give emphasize to the transverse distribution of sea quarks and gluons and show that such measurements will also provide information on the angular momentum sum rule.
RIKEN/BNL Lunch Time Talk
"Jet Fragmentation From Two Dimensional Field Theory"
Presented by Frasher Loshaj, Stony Brook University
Thursday, February 23, 2012, 12:30 pm
Building 510 / Room 2160
Hosted by: Zhongbo Kang
We consider QED_2 (Schwinger Model) as a toy model for studying jet fragmentation in both vacuum and medium. Using the bosonized version of the model, we calculate the fragmentation function of jets in e^+e^ annihilation and find reasonable agreement with the data. We then apply the model to jet quenching in heavy ion collisions, and address the jet fragmentation scaling observed recently at the LHC.
RIKEN/BNL Lunch Time Talk
"Direct photon physics in heavy ion collisions ~Current status and Future~"
Presented by Takao Sakaguchi, Brookhaven National Laboratory
Thursday, February 9, 2012, 12:30 pm
Building 510 / Room 2160
Hosted by: Zhongbo Kang
Direct photons are a promising probe to directly explore the partonic system which are not possible by hadronic probes that are often distorted in the hadronization process. The PHENIX experiments at RHIC measured high pT photons coming from initial hard scattering process in heavy ion collisions for the first time and published in 2005. Then, recently, the experiment came up with low pT photon results, supposedly coming from the hot partonic matter. These measurements characterized the initial state and partonic matter state, but there are states after the collisions yet to be investigated. I will present on the recent results on direct photons from the PHENIX experiments, and then discuss what we can explore with direct photon measurement in the future RHIC runs.
Nuclear Physics & RIKEN Theory Seminar
"Studying 3D structure of proton with neural networks"
Presented by Kresimir Kumericki, University of Zagreb
Friday, February 3, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
3dimensional quarkgluon structure of fast proton, encoded in generalized parton distributions (GPDs), is both a testing ground for QCD and an important input into analysis of protonproton collisions, such as those at LHC. However, extraction of GPDs from experimental data is fraught with uncertainties. After describing the neural network method of data analysis, it will be shown how this method enables elegant and reliable estimation of relevant structure functions. This will be applied to extraction of GPD H from HERMES data on Deeply Virtual Compton Scattering (DVCS).
RIKEN/BNL Lunch Time Talk
"Instantons and sphalerons in magnetic field"
Presented by Grockce Basar, Stony Brook University
Thursday, February 2, 2012, 12:30 pm
Building 510 / Room 2160
Hosted by: Zhongbo Kang
We study the properties of the Euclidean Dirac equation for a light fermion in the presence of both a constant abelian magnetic field and an SU(2) instanton. In particular, we analyze the zero modes analytically in various limits, both on R^4 and on the fourtorus, in order to compare with recent lattice QCD results, and study the implications for the electric dipole moment. We also present a holographic computation of the sphaleron rate in a medium with constant magnetic flux. We show that in the strong field limit, the rate has a linear dependence in B.
Nuclear Physics & RIKEN Theory Seminar
"MassGaps, Gluon massterms and Supersymmetry in D=2+1"
Presented by Abhishek Agarwal, American Physical Society
Friday, January 20, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Rob Pisarski
In this talk  based on work in collaboration with V.P.Nair and A. Fayyazuddin  I'll focus on the mechanism of the dynamical generation of massgaps in the spectrum of three dimensional gauge theories in a gauge invariant formalism; originally due to Kim, Karabali and Nair. I will be particularly interested in addressing the interplay between dynamical massgaps and supersymmetry and present a first principles explanation for the absence of massgaps for N >2 SUSY for YangMills theories [without additional hypermultiplets] in D=3. I will also discuss the compatibility of massgap with minimal supersymmetry and discuss how these results square with many expectations based on other nonperturbative approaches. Finally I will try to comment on a possible generalization of the mechanism of dynamical massgeneration to a manifestly Lorentz invariant framework.
Nuclear Physics & RIKEN Theory Seminar
"Correlations from charge conservation  Determining fundamental properties of the QGP"
Presented by Scott Pratt, Michigan State University
Friday, January 13, 2012, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
Charge correlations from lattice QCD provide insight into the degrees of freedom of the quarkgluon plasma. Charge correlations can also be measured experimentally at RHIC and at the LHC. However, comparing the two has seemed problematic since lattice calculations assume a particle bath while charge is locally conserved in a collision. The situation is further complicated by the dynamics of hadronization. I will show how one can account for effects of local charge conservation and pierce the fog of hadronization to make predictions for experimental correlations that are sensitive to the corresponding quantities measured on the lattice.
RIKEN/BNL Lunch Time Talk
"Ions in biology: Water and Proteins"
Presented by Purushottam Dixit, Brookhaven National Laboratory
Thursday, January 12, 2012, 12:30 pm
Building 510 / Room 2160
Hosted by: Zhongbo Kang
The milieu of all biological activity is a complex electrolyte solution wherein inorganic ions play an important role. Classical electrolyte theory explains some of the activity of ionic species yet more interesting phenomena in biology such as the electrical activity of the heart and firing of neurons rely on the specific chemistry of the ions. We need a statistical mechanical theory to separately understand the role of physics and chemistry in the interaction of ions with biomaterials. The excess free energy of ion hydration/binding contains all the information about the behavior of a given ion in solution. We develop a physically motivated framework to interrogate the different contributors to the excess free energy of an ion. We then apply the framework to the study of Na+(aq). We present a possible explanation for the disparate reports of experimentally determined coordination numbers for Na+(aq). We then apply the same framework and provide an explanation for the long standing puzzle of K+ over Na+ selectivity of the KcsA K+ channel, a membrane protein that excludes the smaller Na+ from the ionic current across neurons while allowing the larger K+ to pass.
Nuclear Physics & RIKEN Theory Seminar
"Multiplicities from blackhole formation in heavyion collisions"
Presented by Anastasios Taliotis, University of Crete
Friday, December 16, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
The formation of trapped surfaces in the headon collision of shock waves in conformal and nonconformal backgrounds is investigated. The backgrounds include all interesting conning and nonconning backgrounds that may be relevant for QCD. Several transverse proles of the shocks are investigated including distributions that fallo as powers or exponentials. Dierent ways of cuttingo the UV contributions (that are expected to be perturbative in QCD) are explored. Under some plausible simplifying assumptions our estimates are converted into predictions for multiplicities for heavyion collisions at RHIC and LHC.
Nuclear Physics & RIKEN Theory Seminar
"Thermalization in collisions of extremely large nuclei at extremely large energies"
Presented by Aleksi Kurkela, McGill University
Friday, December 9, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
Hydrodynamical analysis of experimental data of ultra relativistic heavy ion collisions seems to indicate that the hot QCD matter created in the collisions thermalizes very quickly. Theoretically, we have no idea why this should be true. In my talk, I will describe how the thermalization takes place in the most theoretically clean limit  that of large nuclei at asymptotically high energy per nucleon, where the system is described by weakcoupling QCD. In this limit, plasma instabilities dominate the dynamics from immediately after the collision until well after the plasma becomes nearly in equilibrium at time Qt ~ alpha^(5/2).
Nuclear Physics & RIKEN Theory Seminar
"Recent progress in EFTs for Quarkonium at finite temperature"
Presented by Jacopo Ghiglieri, McGill University, Montreal, Canada.
Thursday, December 8, 2011, 11 am
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
In this talk I will introduce nonrelativistic EFTs of QCD for heavy quarkonium and their generalization to finite temperatures that has been brought forward recently. I will show how this framework allows a systematic treatment of the many scales characterizing the system. I will concentrate on the realization of this framework that is more related to the phenomenology of the Upsilon(1S) and I will show recent developments in the comparison of the widths obtained in this framework with those in the literature.
Joint HET/RIKEN/YITP Seminar
"Hybrid Monte Carlo simulation of graphene"
Presented by Claudio Rebbi, Boston University
Wednesday, December 7, 2011, 2 pm
Building 510 / Room 284
Hosted by: Christoph Lehner
I will briefly review the Hamiltonian of the graphene system and show how the partition function and Green's functions for the quadratic Hamiltonian can be expressed in path integral form by using fermion coherent states. I will then show how one can incorporate the Coulomb interaction into the path integral and how this can be simulated with the hybrid Monte Carlo technique. I will present then early results for the Green's functions obtained with this method. (Based on research done in collaboration with Richard Brower and David Schaich.)
Nuclear Physics & RIKEN Theory Seminar
"QCD phase diagram: universality and continuity"
Presented by Naoki Yamamoto, University of Washington
Friday, December 2, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Rob Pisarski
We discuss the phase diagrams of QCD and QCDlike theories from the viewpoint of the largeNc universality and the quarkhadron continuity. We first show that the whole or the part of the phase diagrams are universal between QCD and QCDlike theories based on the exact largeNc equivalence. We then see that all the QCDlike theories and QCD with threeflavor and threecolor exhibit a quarkhadron continuity at low temperature and finite density. From our universality and QCD inequalities, we derive some rigorous results on the chiral phase transition at large Nc. We also comment on the implications of our results for the recent (and future) lattice QCD simulations.
HighEnergy Physics & RIKEN Theory Seminar
"Flavour Symmetric Sectors and Collider Physics"
Presented by Michael Trott, Perimeter Institute for Theoretical Physics
Wednesday, November 9, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Yingchuan Li
We discuss the phenomenology of effective field theories with new scalar or vector representations of the Standard Model quark flavor symmetry group, allowing for large (aligned) flavor breaking involving the third generation. Such field content can have a relatively low mass scale ≤TeV and O(1) couplings to quarks, while being consistent with both flavor violating and flavor diagonal constraints. These theories therefore have the potential for early discovery at LHC, and provide a flavor safe "tool box" for addressing anomalies at colliders and low energy experiments. We catalogue the possible flavor symmetric representations, and consider applications to the anomalous Tevatron ttbar forward backward asymmetry and Bs mixing measurements. More general collider signatures and constraints on flavor symmetric models are also discussed.
HighEnergy Physics & RIKEN Theory Seminar
"Dark Matter from Minimal Flavor Violation"
Presented by Brian Batell, University of Chicago
Wednesday, November 2, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Yingchuan Li
We consider theories of flavored dark matter, in which the dark matter particle is part of a multiplet transforming nontrivially under the flavor group of the Standard Model in a manner consistent with the principle of Minimal Flavor Violation (MFV). MFV automatically leads to the stability of the lightest state for a large number of flavor multiplets. If neutral, this particle is an excellent dark matter candidate. Furthermore, MFV implies specific patterns of mass splittings among the flavors of dark matter and governs the structure of the couplings between dark matter and ordinary particles, leading to a rich and predictive cosmology and phenomenology. We present an illustrative phenomenological study of an effective theory of a flavor SU(3)_Q triplet, gauge singlet scalar.
HighEnergy Physics & RIKEN Theory Seminar
"Standard Model Prediction of Epsilon_k at NNLO"
Presented by Joachim Brod, University of Cincinnati
Wednesday, October 26, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Yingchuan Li
Neutral Kaon mixing plays an important role in the phenomenology of the standard model and its extensions because of its sensitivity to highenergy scales. In particular epsilon_K, parameterising indirect CP violation, serves as an important constraint on models of new physics, in this way complementing the direct searches at LHC. In order to exploit this sensitivity, a precise standardmodel prediction is crucial. In this seminar I will give a summary of the standardmodel prediction of epsilon_K and the Kaon mass difference Delta M_K, and present our recent NNLO QCD calculation of the contributions eta_ct and eta_cc to the Delta S = 2 effective Hamiltonian. It turns out that the NNLO corrections are very large, and I will discuss the impact on epsilon_K and the theory uncertainties in some detail.
Nuclear Physics & RIKEN Theory Seminar
"Solving the Boltzmann Equation for Relativistic Systems"
Presented by Miller Mendoza Jimenez, ETH, Zurich
Friday, October 14, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Bjoern Schenke
Two Lattice Boltzmann (LB) formulations to solve the relativistic Boltzmann equation are pre sented. The first method is numerically validated and applied to the propagation of shockwave in quarkgluon plasmas and the impact of a supernova blastwave on massive interstellar clouds. The simulations of shock waves are performed in the low and high viscosities regime, using three different computational models, the relativistic lattice Boltzmann (RLB), the Boltzmann Approach Multi Parton Scattering (BAMPS), and the viscous sharp and smooth transport algorithm (vSHASTA). From the comparison of the results, we conclude that the RLB model departs from BAMPS in the case of high speeds and high temperature (viscosities), the departure being due to the fact that the RLB is based on a quadratic approximation of the MaxwellJu ̈ttner distribution, which is only valid for sufficiently low temperature and velocity. Finally, the second method, which is a fully relativistic version of the previous one, is briefly described showing that is capable to handle general geometries and ultrarelativistic cases.
Nuclear Physics & RIKEN Theory Seminar
"Histogram method for the calculation of QCD equation of state at finite density"
Presented by Shinji Ejiri, Niigata University
Friday, October 7, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Frithjof Karsch
We propose a new approach to finite density lattice QCD based on a histogram method and discuss the QCD phase structure at high temperature and density. Because the quark determinant is complex at finite density, the MonteCarlo method cannot be applied directly. We use a reweighting method and try to solve the problems which arise in the reweighting method, i.e. the sign problem and the overlap problem. We discuss the quark mass and chemical potential dependence of the probability distribution function and examine the applicability of the approach.
Nuclear Physics & RIKEN Theory Seminar
"New results on "jet" stopping in AdS/CFT"
Presented by Peter Arnold, University of Virginia
Friday, September 30, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: G. Beuf
At weak coupling, the stopping distance of highenergy partons in QCD and QCDlike plasmas scales with energy as E^(1/2). One may investigate a similar question at strong coupling in QCDlike theories with gravity duals, such as N=4 SUSY YangMills. Various authors have found that the maximum stopping distances in such stronglycoupled theories scales instead as E^(1/3). I will report on work with Diana Vaman showing that there is an important distinction between typical and maximum stopping distances, and the typical stopping distance scales with yet a different power law. I will also try to give some context contrasting different theoretical approaches to using AdS/CFT to study jet stopping and give my take on what, if anything, we learn about the theory of jet stopping from such investigations.
RIKEN Lunch Seminar
"Transverse Spin and Transverse Structure of the Nucleon"
Presented by Jianping Chen, Jefferson Laboratory
Thursday, September 15, 2011, 12:30 pm
Building 510 / Room 2160
Hosted by: Zhongbo Kang
Inclusive DeepInelastic Scattering (DIS) experiments have provided us with the most extensive information on the unpolarized and longitudinal polarized parton (quark and gluon) distributions (PDFs) in the nucleon. It has becoming clear that transverse spin and transverse momentum dependent distributions (TMDs) study are crucial for a more complete understanding of the nucleon structure and the dynamics of the strong interaction (QCD). The transverse spin structure and the TMDs have been the subject of increasingly intense theoretical and experimental study recently. With a high luminosity electron beam facility, JLab has been part of the exploration of this effort. With 12 GeV energy upgrade, Jefferson Lab (JLab) will provide the most precise multidimensional map of the TMDs in the valence quark region through SemiInclusive DIS (SIDIS) experiments, providing a 3d partonic picture of the nucleon in momentum space. Combining with the world data, the transverse spin (transversity) in the valence quark region will be extracted with a good precision and the u and d quark tensor charges of the nucleon will be determined. The precision information on TMDs will also allow a detailed study of the quark orbital motion and its correlation with the quark and the nucleon spins. The planned future ElectronIon Collider (EIC) will greatly expand the kinematical reach to allow a precision study of the TMDs of the sea quarks and gluons, in addition to completing the study in the valence region.
Nuclear Physics & RIKEN Theory Seminar
"A holographic model for large N thermal QCD"
Presented by Mohammed Mia, Columbia University
Friday, September 9, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: G. Beuf
Abstract: We summarize the dual gravity description for a thermal gauge theory, reviewing the key features of our holographic model of large N QCD and elaborating on some new results. The theory has matter in the fundamental representation and the gauge coupling runs logarithmically with energy scale at low energies. At the highest energies the theory becomes approximately scale invariant, much like what we would expect for large N QCD although not with asymptotic freedom. In this limit the theory has a gravity dual captured by an almost classical supergravity description with a controlled quantum behavior, such that by renormalizing the supergravity action, we can compute the stress tensor of the dual gauge theory. From the stress tensor we obtain the shear viscosity and the entropy of the medium at a temperature T , and the violation of the bound for the viscosity to the entropy ratio is then investigated. By considering dynamics of open strings in curved spacetime described by the supergravity limit, we compute the drag and diﬀusion coeﬃcients for a heavy parton traversing the thermal medium. It is shown that both coeﬃcients have a logarithmic dependence on momentum, consistent with pQCD expectations. Finally, we study the conﬁnement/deconﬁnement mechanism for quarks by analyzing open strings in the presence of the ﬂavor seven branes. We ﬁnd linear conﬁnement of quarks at low temperatures, while at high temperatures the quarkonium states melt, a behavior consistent with the existence of a deconﬁned phase.
HighEnergy Physics & RIKEN Theory Seminar
"Observable Scalars from Neutrino Mixing"
Presented by Ernest Ma, UCRiverside
Wednesday, August 24, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: HyeSung Lee
If neutrino mixing comes from a nonAbelian discrete symmetry such A(4), T(7), or Delta(27), the scalars which support such a symmetry in a renormalizable theory may be observable at the Large Hadron Collider. The key is a residual Z(3) symmetry (lepton triality) in the Yukawa sector involving the chargedleptons. Scalars which decay into two different charged leptons, such as mu and tau, or tau and e, are especially important. Their observability at the LHC is discussed.
Nuclear Physics & RIKEN Theory Seminar
"Nonparticle physics of QCD near the phase transition"
Presented by Antal Jakovac, Technical University of Budapest, Budapest
Friday, August 19, 2011, 1:30 pm
Small Seminar Room, Bldg. 510
Hosted by: Peter Petreczky
Treating QCD near the (wouldbe) phase transition temperature, the conventional perturbative approaches (eg. perturbative QCD, chiral perturbation theory) fail, because the theory becomes too strongly interacting. In parallel, the matter properties change from a gaslike plasma of the perturbative regimes to a fluidlike matter. We may still hope to maintain the smallcoupling perturbative description in this regime as well, if we find the adequate degrees of freedom. In the talk I try to argue that the adequate degrees of freedom of QCD in the critical regime are excitations with broad spectral functions. Being not onshell particles, even a noninteracting model of them can show interesting, unexpected properties. I discuss the generic consequences for transport and present model calculations for thermodynamics.
Nuclear Physics & RIKEN Theory Seminar
"Chiral Symmetry and meson gases: recent developments"
Presented by Angel Gómez Nicola, Universidad Complutense, Madrid, Madrid
Friday, August 12, 2011, 1:30 pm
Small Seminar Room, Bldg. 510
Hosted by: G. Beuf
"I will discuss some recent results on light meson gases, which may be of relevance for Heavy Ion and Nuclear Matter physics. These include thermal resonances and their relation to chiral symmetry restoration, chemical nonequilibrium effects, transport coefficients and isospin breaking. The basic framework is Chiral Perturbation Theory, which ensures the model independency of the lowenergy and lowtemperature regimes, combined with unitarity when an accurate analytical description of scattering is needed, as for the thermal width and transport coefficients. "
Nuclear Physics & RIKEN Theory Seminar
"Angular correlations in gluon emission ("ridge") from high energy QCD"
Presented by Michael Lublinsky, Ben Gurion University of the Negev
Friday, July 29, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: G. Beuf
I will discuss angular and rapidity correlations in twoparticle inclusive production ("ridge") in pp and AA collisions. Such correlations arise naturally in the theory of high energy QCD. A new insight based on solutions of the BalitskyKovchegov equation will be presented.
Nuclear Physics & RIKEN Theory Seminar
"Acoustic oscillations in higher harmonics of Big and Little Bangs"
Presented by Pilar Staig & Edward Shuryak, Stony Brook University
Friday, July 22, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: G. Beuf
We study the effect that initial state fluctuations have on final particle correlations in heavy ion collisions. More precisely, we focus on the propagation of initial perturbations on top of the expanding fireball using the conformal solution derived by Gubser and Yarom for central collisions. The hydrodynamic equations are solved by separation of variables and the solutions for different modes are added up to construct initial pointlike perturbations, that are then allowed to evolve until freezeout. The CooperFrye prescription is used to determine the final particle distribution. We present the twoparticle correlation functions and their Fourier spectra obtained for different viscosities. We find that viscosity kills the higher harmonics, but that the Fourier spectra presents maxima and minima, similar to what is seen in the study of Cosmic Background Radiation. The difference between the first and the second maximum is used to estimate the viscosity of the medium.
Nuclear Physics & RIKEN Theory Seminar
"Nuclear Matter Properties, Clustering at the Nuclear Surface and Symmetry Energy"
Presented by Qamar Usmani, University Malaysia Perlis, Malaysia
Friday, July 15, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: G. Beuf
We present a phenomenological theory of nuclei which incorporates clustering at the nuclear surface in a general form. The theory explains the recently reported large values of symmetry energy by Natowitz et al at low densities of nuclear matter and is fully consistent with the static properties of nuclei. In phenomenological way clusters of all sizes, shapes along with medium modifications are included. Nuclear matter properties are discussed in detail. Arguments are given which lead to an equation of state of nuclear matter consistent with clustering. As a framework, an extended version of Thomas Fermi theory is adopted. This connects the nuclear matter equation of state, which incorporate clustering at low densities, with clustering in nuclei at the nuclear surface. Calculations are performed for various equation of state of nuclear matter consistent with clustering. The importance of quartic term in symmetry energy is demonstrated at and below the saturation density in nuclear matter. It is shown that it is related both to clustering as well as to the contribution of threenucleon i nteraction to the equation of state of neutron matter. Reasons for these are discussed. Merits of the results with clustering and noclustering are discussed. Due to clustering the neutron skin thickness in nuclei, fundamental to neutron star studies, is found to reduce significantly. An estimate of the spinodal density of symmetric nuclear matter is given. Theory predicts new situations and regimes to be explored both theoretically and experimentally.
Nuclear Physics & RIKEN Theory Seminar
"Highenergy Amplitudes and Impact Factors at nexttoleadingorder"
Presented by Giovanni Chirilli, Lawrence Berkeley National Laboratory
Friday, July 8, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: ZhongBo Kang
I will review the calculation of the highenergy amplitudes and impact factors in QCD and in N =4 SYM theory at nexttoleading order using the operator product expansion in terms of composite Wilson line operators.
Nuclear Physics & RIKEN Theory Seminar
"Hadron structure from exclusive measurements"
Presented by Adam Szczepaniak, Indiana University
Friday, July 1, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: G. Beuf
The is a renewed interest in exclusive reactions. Electromagnetic form factors and Generalized Parton Distribution are examples of hadronic properties to be accessed in exclusive, photon induced transitions. I will discuss old and new ideas on partonic description of such properties.
Nuclear Physics & RIKEN Theory Seminar
"Transverse momentum distributions from effective field theory"
Presented by Prof. Frank Petriello, Northwestern University & Argonne National Laboratory
Friday, May 6, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: G. Beuf
We present an approach to the resummation of low transversemomentum logarithms using Softcollinear Effective Theory. This method naturally avoids several problems that affect the standard approach. After motivating the importance of this phasespace region for experimental analyses, we explain the approach. Numerical results and a discussion of the open issues are presented.
Nuclear Physics & RIKEN Theory Seminar
"Quark matter conductivity in strong magnetic field"
Presented by Boris Kerbikov, ITEP, Moscow, Russia
Friday, April 29, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: G. Beuf
Recently it was realized that heavyion collisions generate a gigantic magnetic field.It has been argued that the relaxation time of this field crucially depends on electrical conductivity of quark matter.A related quantity,namely chiral conductivity,plays the central role in Chiral Magnetic Effect. Using ideas and methods developed in condensed matter physics we derive equations for quantum conductivity in three and two dimensions( d=2 corresponds to Lorentz contracted ions) with magnetic field varying from zero to maximal RHIC values. We believe that the results remain true beyond the simple model used in their derivation.
Nuclear Physics & RIKEN Theory Seminar
"Recent Observations of and Theoretical Implications for Neutron"
Presented by Jim Lattimer, Stony Brook University
Friday, April 22, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: G. Beuf
Recent observations of neutron stars in radio, visible and Xray radiation are able to significantly constrain the properties of cold, dense matter. These observations include the discovery of a nearly 2 solar mass neutron star from pulsar timing, simultaneous mass and radius estimates from Xray bursters and cooling quiescent stars, and detection of the rapid cooling of the Cassiopeia A supernova remnant. These have limited the range of equations of state for neutron star matter and severely restrict the roles that quark matter has in their interiors. Limits to the critical temperatures for a neutron superfluid and a proton superconductor in the core of neutron stars are also suggested.
Nuclear Physics & RIKEN Theory Seminar
"Gauge symmetry and spin structure of the proton"
Presented by Xiangdong Ji, University of Maryland
Wednesday, April 6, 2011, 11 am
Small Seminar Room, Bldg. 510
Hosted by: G. Beuf
Recently, there has been a flurry of activities about gauge symmetry constraints on the spin structure of the proton. I will discuss the new proposals.
Nuclear Physics & RIKEN Theory Seminar
"Orbifold equivalence in largeN QCD with finite baryon chemical potential and the sign problem"
Presented by Masanori Hanada, University of Washington, Seattle
Friday, April 1, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: G. Beuf
We point out that largeN_c QCD in the 't Hooft limit is equivalent to SO(2*N_c) YangMills theory with fundamental fermions. In the latter, notorious "sign problem" is absent even with finite baryon chemical potential, and hence the MonteCarlo simulation is applicable. We also show the same idea can be applied in related models  chiral random matrix theory (RMT) and holographic models. We explain nice old results like the exactness of the phase quenching in RMT in a certain parameter region is naturally understood and is generalized from the point of view of the equivalence. This talk is based on works with A. Cherman and D. RoblesLlana (Phys. Rev. Lett. 106, 091603), with N. Yamamoto (in preparation) and with C. Hoyos, A. Karch and L. Yaffe (in preparation).
HighEnergy Physics & RIKEN Theory Seminar
"Electromagnetic Splitting of Charged and Neutral Mesons"
Presented by Aaron M. Torok, Indiana University
Wednesday, March 30, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Oliver Witzel
We calculated the electromagnetic splittings of charged and neutral mesons, and the violation of Dashen's theorem. The meson masses are calculated with Lattice QCD using the MILC ensembles. U(1) gauge fields are generated independently. The computationally intensive part of the SU(3)xU(1) calculation is done using an implementation of the MILC staggered multimass inverter that originally ran on one GPU, and now runs on many. An extrapolation to the physical point is underway using staggered chiral perturbation theory.
HET/RIKEN Lunch Seminar
"Generic dark matter signature for gammaray telescopes"
Presented by WaiYee Keung, University of Illinois, Chicago
Friday, March 25, 2011, 12 pm
Building 510 / Room 2160
Hosted by: A. Soni
We describe a characteristic signature of dark matter (DM) annihilation or decay into gammarays. We show that if the total angular momentum of the initial DM particle(s) vanishes, and helicity suppression operates to prevent annihilation/decay into light fermion pairs, then the amplitude for the dominant 3body final state e+e gamma has a unique form dictated by gauge invariance. This amplitude and the corresponding energy spectra hold for annihilation of DM Majorana fermions or selfconjugate scalars, and for decay of DM scalars, thus encompassing a variety of possibilities. Within this scenario, we analyze Fermi LAT, PAMELA and HESS data, and predict a hint in future Fermi gammaray data that portends a striking signal at atmospheric Cherenkov telescopes (ACTs).
Nuclear Physics & RIKEN Theory Seminar
"Viscous hydrodynamic radial and elliptic flow from RHIC to LHC"
Presented by Chun Shen, Ohio State University
Friday, March 18, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: G. Beuf
Using viscous hydrodynamics and a stateoftheart equation of state,s95pPCE, we explore the dependence of the final observed hadron spectra and elliptic flow on the input parameters, in particular shear viscosity. Based on these experiences, we present an excellent fit for the spectra and elliptic flow of all charged hadrons as well as identified pions and protons from Au+Au collisions of all centralities measured at the relativistic Heavy Ion Collider (RHIC). Taking this global fit as starting point, we extrapolate to higher Large Hadron Collider (LHC) energies and predict the analogous observables for Pb+Pb collisions at √s =2.76 and 5.5ATeV, assuming the same constant specific shear viscosity η/s and thermalization time at both collision energies. Comparison with recent ALICE measurements of the elliptic flow of charged hadrons shows that the model slightly overpredicts the data. This indicates some possible temperature dependence of (η/s)(T), and I will show some results when I explain this possibility. Future experiments will further test the model and shed additional light on possible variations of the quarkgluon transport coefficients between RHIC and LHC energies.
Nuclear Physics & RIKEN Theory Seminar
"QCD and Beyond on the Lattice"
Presented by Meifeng Lin, Yale University
Friday, March 11, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: G. Beuf
The theory that describes strong interactions between quarks and gluons, quantum chromodynamics (QCD), has a coupling strength that is stronger at low energies, making it implausible to study lowenergy physics using perturbation theory. Discretizing it on a spacetime lattice is the only known way to study strong interactions from first principles. I will give an overview of lattice QCD and focus on its applications in nucleon structure calculations. Using the lattice approach to study other QCDlike theories will also be briefly discussed.
Nuclear Physics & RIKEN Theory Seminar
"Jet Tomography and Particle Correlations in HeavyIon Collisions"
Presented by Barbara Betz, Columbia University
Friday, March 4, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: G. Beuf
Heavyion collisions offer the possibility to study matter under extreme conditions of high temperatures and densities in the laboratory. Jets and jetmedium correlations can probe the highenergydensity matter created in such collisions. Azimuthal correlations suggest that conical wakes are induced and have been interpreted as evidence for the creation of Mach cones due to the propagation of a supersonic parton. In this talk, the efforts and the progress in understanding the medium response to the propagation of a supersonic jet will be critically reviewed and the recent developments will be reported. Moreover, the sensitivity of the azimuthal dependence of single and dihadron nuclear modification factors to the fluctuation spectrum of initial geometric inhomogeneities will be investigated comparing Glauber and KLN Monte Carlo models, leading into a discussion on how average azimuthal moments could help to differentiate between the geometrical ensembles.
HighEnergy Physics & RIKEN Theory Seminar
"A new perspective on CP violation in three body decays"
Presented by Monika Blanke, Cornell University
Wednesday, March 2, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: A. Soni
I discuss the potential of measuring CP violation in three body decays, paying particular attention to the different possible origins of the "strong" CPeven phase. This phase can be obtained from the propagation of intermediate state particles  either when diagrams with different intermediate particles interfer, or when the intermediate state is offshell by a different amount. I will elaborate mainly on the second case here which has not yet received much attention in the literature. After analysing a simple toy model I apply our findings to a specific example, namely neutralino decay in the MSSM.
Nuclear Physics & RIKEN Theory Seminar
"Holography and the collision of gravitational waves in asymptotically AdS_5 spacetime"
Presented by Paul Chesler, MIT
Friday, February 25, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: G. Beuf
In recent years holography has emerged as a powerful tool to study nonequilibrium phenomena in certain quantum theories, mapping challenging quantum dynamics onto the classical dynamics of gravitational fields in one higher dimension. One interesting process which can be addressed with holography is the collision of sheets of matter in strongly coupled nonAbelian gauge theories. The collision results in the creation of a quarkgluon plasma which at late times behaves as a nearly ideal liquid. In the dual gravitational description, this process maps onto the process of gravitational collapse and black hole formation in asymptotically AdS_5 spacetime. I will describe how one can use techniques from numerical relativity to study this process.
Nuclear Theory/Riken Seminar
"Diagrammatic method for computing transport coefficients near the chiral phase transition"
Presented by Yoshimasa Hidaka, Kyoto University
Friday, February 11, 2011, 2 pm
Small Seminar Room, Bldg. 510
We propose a novel diagrammatic method for computing transport coefficients in relativistic quantum field theory. The selfconsistent equation for summing the diagrams with pinch singularities has a form of a linearized kinetic equation as usual, but our formalism enables us to incorporate higher oder corrections of the coupling systematically. We apply our formalism to a simple model with chiral symmetry, and discuss the behavior of the transport coefficients around the chiral phase transition at finite temperature.
HighEnergy Physics & RIKEN Theory Seminar
"Exploring 8 and 12 Flavor QCD"
Presented by Robert Mawhinney, BNL
Wednesday, February 9, 2011, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Oliver Witzel
QCD with many light quark flavors may have a conformal phase, before the theory loses asymptotic freedom. We report on extensive simulations of 8 and 12 flavor QCD, where we have measured light hadron masses, decay constants and the string tension at zero temperature. We have also observed the finite temperature transition for 8 flavors and seen that it is first order. This data supports 8 and 12 flavor QCD being in the conventional, chirally broken phase, in contrast to other studies measuring the beta function.
Nuclear Physics & RIKEN Theory Seminar
"Jets, Machcone, hot spots, ridges and harmonic flow  the landscape in dihadron correlation"
Presented by XinNian Wang, LBNL
Friday, January 28, 2011, 2 pm
Small Seminar Room, Bldg. 510
Fluctuations in initial parton production in highenergy heavyin collisions lead to irregular initial transverse energy density distribution with hot spots and valleys that are also extended in rapidity. These irregular initial density distribution will lead to finite harmonic flow in hadron distribution through collective expansion even in the most central heavyion collisions. I will discuss dihadron correlations from dijets, jetinduced Machcone and expanding hot spots, after subtraction of contributions from harmonic flow. Comparison between dihadron and gammahadron correlation will further differentiate correlations from Machcone and expanding hot spots. The ridgelike structure of these net diahdron correlation in the longitudinal direction is also discussed
Nuclear Physics & RIKEN Theory Seminar
"Deconfinement in YangMills theory through toroidal"
Presented by Mithat Unsal, Stanford University
Friday, December 10, 2010, 2 pm
Small Seminar Room, Bldg. 510
We introduce field theory techniques through which the deconfinement transition of fourdimensional YangMills theory can be moved to a semiclassical domain where it becomes calculable using twodimensional field theory. The two dimensional theory has electric and magnetic (order and disorder) perturbations, analogs of which appear in planar spinsystems and statistical physics. In this regime, the deconfinement transition is driven by the competition between electric and magnetic perturbations.
Nuclear Physics & RIKEN Theory Seminar
"Thermal Quark and Gluon Distributions in the PNJL model"
Presented by HungMing Tsai, Duke University
Friday, December 3, 2010, 2 pm
Small Seminar Room, Bldg. 510
In this talk, we explore the dynamics of gluons in the NambuJonaLasinio model with Polyakov loop (PNJL model) within the meanfield approximation. We first calculate the fundamental Polyakov loop by minimizing the PNJL action and then obtain the adjoint Polyakov loop by demanding selfconsistency with the GockschOgilvie effective action for the eigenvalues of the Polyakov loop. We then derive the quark and gluon number densities and other thermodynamic quantities as functions of temperature and chemical potential. We explain why the deconfinement transition is much faster for light quarks than for gluons
Nuclear Physics & RIKEN Theory Seminar
"Jet quenching in DIS and heavyion collisions: moving towards a more quantitative approach"
Presented by Abhijit Majumdar, Ohio State University
Thursday, November 18, 2010, 12:30 pm
Bldg 510, room 2220
Hosted by: Rob Pisarski
The modification of hard jets in dense extended media such as large nuclei or a deconfined quark gluon plasma will be described in a factorized formalism where the hard partons couple weakly with the medium, where the medium may itself be strongly or weakly coupled. The effect of the medium will be parametrized in a handful of transport coefficients which are obtained as the inmedium expectation of well defined operator products. We will attempt to describe the attenuation of the yield of leading hadrons in DIS and heavyion collisions (HIC) as well as the centrality, azimuthal anisotropy and flavor dependence (in HIC) in a single formalism. Also preliminary results from a new MonteCarlo event generator based on this formalism will be presented.
HighEnergy Physics & RIKEN Theory Seminar
"Monopoles, bions, and other oddballs in confinement or conformality"
Presented by Erich Poppitz, University of Toronto
Wednesday, November 10, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Oliver Witzel
I will explain how compactification on a small (nonthermal) circle yields a regime where the study of supersymmetric and nonsupersymmetric nonperturbative gauge dynamics comes under theoretical control. I will review recent developments in this area and discuss possible directions for future work.
HighEnergy Physics & RIKEN Theory Seminar
"Flavor oscillations of supernova neutrinos and the observation of the neutrino signal in the DUSEL detector"
Presented by Alexander Friedland, Los Alamos National Laboratory
Wednesday, October 6, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Hooman Davoudiasl
Nuclear Physics & RIKEN Theory Seminar
"k_tfactorization for hard processes in nuclei"
Presented by Fabio Dominguez, Columbia University
Friday, October 1, 2010, 1 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
Two widely proposed $k_t$dependent gluon distributions in the small$x$ saturation regime are investigated using two particle backtoback correlations in high energy scattering processes. The Weizs\"{a}ckerWilliams gluon distribution, interpreted as the number density of gluons inside the nucleus, is studied in the quarkantiquark jet correlation in deep inelastic scattering. On the other hand, the unintegrated gluon distribution, defined as the Fourier transform of the colordipole cross section, is probed in the direct photonjet correlation in $pA$ collisions. Dijetcorrelation in $pA$ collisions depends on both gluon distributions through combination and convolution in the large $N_c$ limit. We calculate these processes in two approaches: the transverse momentum dependent factorization approach and the colordipole/color glass condensate formalism, and they agree with each other completely.
Nuclear Physics & RIKEN Theory Seminar
"Better understanding the relation between the JIMWLK Hamiltonian and the BFKL limit"
Presented by Alex Kovner, University of Connecticut
Wednesday, September 22, 2010, 3:15 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
I discuss the relation between the eigenfunctions and eigenvalues of the JIMWLK Hamiltonian and those of its low density limit  the BFKL Hamiltonian. I show that the eigenfunctions get corrections in the perturbation theory (expansion in powers of the charge density), while the eigenvalues do not. I also explain how the bootstrap condition arises automatically from the JIMWLK/KLWMIJ framework as direct consequence of the hermiticity of the Hamiltonian. Leading correction to the BFKL reggeized gluon wave function is calculated.
Nuclear Physics & RIKEN Theory Seminar
"'An effective chiral Equation of State including hadronic and quark degrees of freedom"
Presented by Jan SteinheimerFroschauer, Goethe University Frankfurt, Germany
Friday, September 3, 2010, 2 pm
Small Seminar Room, Bldg. 510
We combine, in a single model, a wellestablished flavorSU(3) hadronic model with a quarkgluon description of the highly excited matter. This allows us to study the chiralsymmetry and confinementdeconfinement phase structure of strongly interacting matter at high temperatures and densities. In addition we obtain an equation of state of hadronic and quark matter that is applicable over a wide range of thermodynamical conditions. I will present results on the thermodynamics of the model, compared to recent lattice data, as well as the phase structure in temperature and baryochemical potential. In this context I will also highlight the influence of heavy hadronic resonances on the chiral phase transition. Furthermore I will discuss the temperature dependence of the baryon number susceptibilities for different parametrizations of the model and compare the results to lattice data and results obtained with a basic PNJL model.
Nuclear Physics & RIKEN Theory Seminar
"MonteCarlo simulation of heavyion collisions"
Presented by Bjoern Schenke, McGill University
Friday, August 27, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
I present the Modular Algorithm for Relativistic Treatment of heavy IoN Interactions (MARTINI), a MonteCarlo simulation of high energy heavyion collisions. Its main components are PYTHIA 8.1, a time evolution model for the soft background, and a parton evolution scheme, currently the McGillAMY formalism including radiative as well as elastic processes. MARTINI generates full event configurations in the high p_T region that take into account thermal QCD and QED effects as well as effects of the evolving medium. I will show latest results for hard observables in Au+Au and Cu+Cu collisions at RHIC energies, using different fluiddynamic calculations for the soft background evolution. I further present first correlation studies and discuss MARTINI's potential to provide input for full jet reconstruction algorithms.
Nuclear Physics & RIKEN Theory Seminar
"ETQS matrix element and the sign reversal of the Sivers function"
Presented by Andreas Metz, Temple University
Friday, August 20, 2010, 2 pm
Small Seminar Room, Bldg. 510
The twist3 ETQS (EfremovTeryaevQiuSterman) matrix element, which has a direct relation to the Sivers parton distribution, plays a very important role in the phenomenology of transverse single spin asymmetries measured at RHIC in protonproton collisions. We discuss new results showing that the ETQS matrix element can also be addressed, for instance, in e+p > jet+X in a rather clean way. This matrix element also shows up e+when describing transverse single spin asymmetries for Wproduction at RHIC. It is argued that the latter observable is very promising in order to check the predicted sign reversal of the Sivers function.
Nuclear Physics & RIKEN Theory Seminar
"Strong to weak coupling transition in large Nc QCD"
Presented by Rajamani Narayanan, Florida International University
Friday, August 6, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
"Twodimensional chiral fermions coupled to four dimensional gauge fields will be used as a probe to properly quantify the large Nc strong to weak coupling transition."
Nuclear Physics & RIKEN Theory Seminar
"The nuclear liquidgas phase transition at large $N_c$ in the Van der Waals approximation"
Presented by Giorgio Torrieri, Columbia University
Friday, July 30, 2010, 2 pm
Small Seminar Room, Bldg. 510
The nuclear liquidgas phase transition at large $N_c$ in the Van der Waals approximation We examine the nuclear liquidgas phase transition at large number of colors ($N_c$) within the framework of the Van Der Waals (VdW) model. We argue that the VdW equation is appropriate at describing internucleon forces , and discuss how each parameter scales with $N_c$. We demonstrate that $N_c=3$ is not large with respect to the other dimensionless scale relevant to baryonic matter, the number of neighbours in a dense system. Consequently, we show that the liquidgas phase transition looks dramatically different at $N_c \rightarrow \infty$ with respect of our world: The critical point temperature becomes of the order of $\lqcd$ rather than below it. The critical point density becomes of the order of the baryonic density, rather than an order of magnitude below it. These are precisely the characteristics usually associated with the ``Quarkyonic phase''. We therefore argue that at large $N_c$ the nuclear liquid phase coincides with the conjectured quarkyonic phase, although the two are thought to occur at very different scales in our world.
Nuclear Physics & RIKEN Theory Seminar
"Thermal Conductivity Of Quark Matter In The CFL Phase"
Presented by Jingyi Chao, North Carolina State University
Friday, July 23, 2010, 2 pm
Small Seminar Room, Bldg. 510
I briefly review the formation of color superconductivity which happen in compact stars. Below the temperature scale set by the gap in the quark spectrum, transport properties are determined by collective modes. We compute the thermal conductivity, $\kappa$, of colorflavor locked (CFL) quark matter in the frame of kinetics theory. We present and compare the result with previous estimates. We also conclude a CFL quark matter core of the compact star becomes isothermal on a timescale of a few seconds.
Nuclear Physics & RIKEN Theory Seminar
"QCD with chemical potential in a small hyperspherical box"
Presented by Joyce Meyers, Swansea University, UK
Friday, July 9, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
We consider the phase diagram of QCD formulated in small spatial volumes. The beneﬁt of the small spatial volume is that it allows for a perturbative calculation of the phase diagram which is valid for all temperatures and densities. The action of QCD is complex when the quarks are coupled to a nonzero chemical potential. This results in the sign problem which prevents lattice simulations using conventional techniques. From oneloop perturbation theory on S^1 x S^3 we calculate the phase diagram analytically in the T − mu plane in the large N and Nf limit by generalizing large N matrix model techniques for the case of a complex action. We compare with low temperature results for N = 3 obtained by performing the integrals over the gauge ﬁelds numerically. We calculate expectation values for several observables including the fermion number and the Polyakov lines. For the fermion number a Landaulevellike structure is observed as a function of the chemical potential and each level transition coincides with a spike in the Polyakov lines, indicating partialﬁlling of the level. In the large N limit each level transition corresponds to discontinuities in the fermion number which result in thirdorder transitions of the GrossWittenWadia type. We confirm the appearance of the levelstructure at low temperatures in lattice simulations of 2color QCD where the sign problem is absent.
Nuclear Physics & RIKEN Theory Seminar
"Induced gluon radiation in QCD matter and jet quenching"
Presented by Bronislav Zakharov, Landau Institute
Friday, July 2, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
We discuss parton energy loss in QCD matter within the lightcone path integral approach to the induced gluon emission. In the first part of the talk we give a short introduction to the formalism. Then we discuss the radiative energy loss in a static brick of quarkgluon plasma. In the second part of the talk we present the results for the energy loss and jet quenching in expanding quarkgluon plasma for RHIC and LHC energies. At the end of the talk we discuss the anomalous baryon production and synchrotron energy loss.
Nuclear Physics & RIKEN Theory Seminar
"Dielectron production from full 3D hydrodynamic model with spectral constraint"
Presented by Yukinao Akamatsu, University of Tokyo, Japan
Friday, June 25, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
The dielectron production from the medium in the low invariant mass region is calculated from the full 3D hydrodynamic model. The dielectron rate is related to the inmedium spectral function of vector modes. The vector spectral function in all temperature is modeled with a constraint from QCD sum rule. We show that the dependence of the dielectron spectra on the equation of state is large and that it is one of the main causes for the discrepancy between the theoretical calculation and the experimental data of dielectrons at PHENIX. We also point out that the contribution of the dielectrons produced from the bremsstrahlung in hadronic reaction is quite large below the two pion threshold.
HighEnergy Physics & RIKEN Theory Seminar
"Living in Extra Dimensions"
Presented by Argyris Nicolaidis, Aristotle University of Thessaloniki, Greece
Wednesday, June 9, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Yannis Semertzidis
In models unifying gravity and the other forces, gravity propagates, besides the usual four dimensions, into additional δ extra dimensions and gravity becomes strong at TeV energies. We look for signatures of extra dimensions and strong gravitational phenomena in cosmic rays, attributing the cosmic ray to produced gravitons, escaping in the extra dimensions LHC, with the production of microscopic black holes unconventional neutrino oscillations, where a flavor neutrino mixes with a singlet neutrino living in the bulk photon mixing with an axion living in extra dimensions, providing new explanations for the transparency of the universe to high energy photons and for the dispersion of time arrival of the MAGIC photons in cosmic rays, LHC physics, high energy neutrinos, and the astrophysics of high energy photons.
Nuclear Physics & RIKEN Theory Seminar
"Spectral Densities for Hot QCD Plasmas in a LeadingLog Approximation"
Presented by Juhee Hong, SUNY Stony Brook
Friday, June 4, 2010, 2 pm
Small Seminar Room, Bldg. 510
The leadinglog Boltzmann equation is solved numerically with nontrivial boundary conditions. We present the spectral densities of J^\mu and T^\mu\nu at small frequencies : current, shear, sound, bulk, and transverse tensor channel. They exhibit a smooth transition from free streaming quasiparticles to ideal hydrodynamics. This transition is analyzed with second order hydrodynamics and compared with AdS/CFT.
Nuclear Physics & RIKEN Theory Seminar
"Viscosity of Strongly Interacting Fermi Gases"
Presented by Mohit Randeria, Ohio State University
Friday, May 14, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
Transport in strongly interacting systems, which may not support welldefined quasiparticle excitations, is a subject of great interest in diverse fields ranging from condensed matter physics to nuclear physics and string theory. In this talk I will describe recent work on the viscosity of nonrelativistic quantum fluids, with a particular focus on strongly interacting ultracold Fermi gases. I will discuss exact nonperturbative results based on spectral functions and sum rules, and conclude with a proposal for a spectroscopic measurement of the shear viscosity spectral function in the unitary Fermi gas.
RIKEN Lunch Seminar
"Lowenergy constants from Dirac eigenvalue correlators at NNLO in the epsilon expansion"
Presented by Christoph Lehner, RBRC, Germany
Thursday, May 6, 2010, 12:30 pm
Bldg. 510, Room 2160
Hosted by: Anthony Baltz
We calculate the nexttonexttoleading order (NNLO) contributions in the epsilon expansion with a small imaginary chemical potential and discuss their relevance to Dirac eigenvalue correlators. We show how to minimize systematic deviations from randommatrix theory by an optimal choice of lattice geometry in the case of two light quark flavors. Finally, we determine the lowenergy constants Sigma and F from configurations of JLQCD with two dynamical overlap fermions.
Nuclear Physics & RIKEN Theory Seminar
"Holographic approach for the effects of nuclear density and gluon condensation"
Presented by Bumhoon Lee, Sogang University, Seoul, Korea
Friday, April 30, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
We identify the dual geometry of the hadron phase of dense nuclear matter and investigate the confinement/deconfinement phase transition. We suggest that the low temperature phase of the RN black hole with the full backreaction of the bulk gauge field is described by the zero mass limit of the RN black hole with hard wall. We calculated the density dependence of critical temperature, meson masses and decay constants. We also describe the thermodynamics of the gluon condensation including the effect of the HawkingPage transition
Joint HET/RIKEN/YITP Seminar
"Quantum Criticality and the Cuprate Superconductors"
Presented by Subir Sachdev, Harvard University
Wednesday, April 28, 2010, 2 pm
Large Seminar Room, Bldg. 510
Hosted by: Sally Dawson
I will begin with a simple introduction to the theory of quantum criticality, as applied to experiments on certain insulating antiferromagnets. I will then survey the phenomenology of the cuprate high temperature superconductors, and show how ideas from quantum criticality have helped explain or predict the results of a number of recent experiments. The applications to the cuprates focus attention on key problems associated with the criticality of Fermi surfaces in two dimensions which remain unresolved. I will describe how these open problems are being addressed by the AdS/CFT correspondence discovered in string theory.
Nuclear Physics & RIKEN Theory Seminar
"Comprehensive Solution to the Cosmological Constant, ZeroPoint Energy, and Quantum Gravity Problems"
Presented by Philip Mannheim, University of Connecticut
Friday, April 23, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
We present a solution to the cosmological constant, the zeropoint energy, and the quantum gravity problems within a single comprehensive framework. We show that in quantum theories of gravity in which the zeropoint energy density of the gravitational field is welldefined, the cosmological constant and zeropoint energy problems solve each other by mutual cancellation between the cosmological constant and the matter and gravitational field zeropoint energy densities. Because of this cancellation, regulation of the matter field zeropoint energy density is not needed, and thus does not cause any trace anomaly to arise. We exhibit our results in two theories of gravity that are welldefined quantummechanically. Both of these theories are locally conformal invariant, quantum Einstein gravity in two dimensions and Weyltensorbased quantum conformal gravity in four dimensions (a fourthorder derivative quantum theory of the type that Bender and Mannheim have recently shown to be ghostfree and unitary). Central to our approach is the requirement that any and all departures of the geometry from Minkowski are to be brought about by quantum mechanics alone. Consequently, there have to be no fundamental classical fields, and all mass scales have to be generated by dynamical condensates. In such a situation the trace of the matter field energymomentum tensor is zero, a constraint that obliges its cosmological constant and zeropoint contributions to cancel each other identically, no matter how large they might be. In our approach quantization of the gravitational field is caused by its coupling to quantized matter fields, with the gravitational field not needing any independent quantization of its own. With there being no a priori classical curvature, one does not have to make it compatible with quantization.
Nuclear Physics & RIKEN Theory Seminar
"Collision geometry fluctuations and triangular flow in heavyion collisions"
Presented by Burak Alver, MIT
Friday, April 16, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
It was suggested that fluctuations in the initial geometry of ultrarelativistic heavy ion collisions can provide an explanation for the surprisingly large elliptic flow values observed in central Cu+Cu collisions. Measurement of elliptic flow fluctuations in Au+Au collisions has confirmed the existence of such large geometry fluctuations. In this talk, I will discuss how the same principle of initial geometry fluctuations may also be the key to understanding the "ridge" and "broad away side" structures present in two particle correlation measurements. I will introduce the concepts of participant triangularity and triangular flow, analogous to the definitions of participant eccentricity and elliptic flow. The participant triangularity characterizes the triangular anisotropy of the initial nuclear overlap geometry and arises from eventbyevent fluctuations in the participantnucleon collision points. In studies using a multiphase transport model (AMPT), a triangular flow signal is observed that is proportional to the participant triangularity and corresponds to a large third Fourier coefficient in twoparticle azimuthal correlation functions. Ratios of the second and third Fourier coefficients of two particle azimuthal correlations are observed to exhibit similar trends in experimental data and AMPT calculations as a function of centrality and transverse momentum, suggesting a similar origin. Triangular flow provides a new handle on the initial collision geometry and collective expansion dynamics in heavyion collisions.
HighEnergy Physics & RIKEN Theory Seminar
"SUSY and Hidden Sector Extensions with Dark Matter and LHC Signatures"
Presented by Daniel Feldman, University of Michigan
Wednesday, April 14, 2010, 2 pm
Small Seminar Room, Bldg. 510
Discussed are high scale models of supersymmetry and hidden sector extensions of the minimal framework. LHC signatures of new physics are connected to recent data driven probes of dark matter scattering. Implications for the annihilation of dark matter in the galaxy are also discussed including proposed solutions to the cosmic anomalies reported in the PAMELA Satellite data.
Nuclear Physics & RIKEN Theory Seminar
"Is the scaling of v2 in heavy ion collisions natural?"
Presented by Giorgio Torrieri, JW Goethe Universitaet, Frankfort, Germany
Friday, April 9, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
We examine the "naturalness" of the scaling of multiplicity and elliptic flow $v_2$ with rapidity in weakly and strongly coupled systems. We show that multiplicity scaling is relatively straightforward to incorporate in existing ansatze with no unnatural assumptions, and argue that this scaling is relatively insensitive to the transport properties of the system. On the other hand, we argue that the observed scaling of elliptic flow observed is problematic to describe within a hydrodynamic model (the Knudsen number $K \ll 1$), but arises more naturally within weakly coupled systems (where the Knudsen number $\sim 1$). We conclude by an overview of ways proposed to make weakly coupled systems compatible with the absolute value of elliptic flow, and by indicating experimental probes which could clarify these issues
HighEnergy Physics & RIKEN Theory Seminar
"A Dark Matter Explanation of the Fermi, PAMELA, and WMAP Results"
Presented by Lisa Goodenough, New York University
Wednesday, April 7, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Ruth Van der Water
Multiple lines of evidence indicate an anomalous injection of highenergy electrons and positrons in the Galactic halo. PAMELA has measured a sharp rise in the positron fraction up to 80 GeV. Fermi has found a hardening of the total electronic cosmic ray spectrum above 100 GeV with a break confirmed by HESS at around 1 TeV. Excess microwaves toward the Galactic center in the WMAP data (the WMAP "haze") are consistent with hard synchrotron radiation from a population of 10100 GeV electrons and positrons. A recently analysis of the Fermi gammaray sky suggests that there is a gammaray counterpart to the microwave haze in the Galactic Center. I will explain how dark matter annihilations, dominantly through leptonic modes, either directly or through a new light boson, can provide a consistent explanation of all of these data.
Nuclear Physics & RIKEN Theory Seminar
"Integrability of gauge theories: a tool for QCD?"
Presented by Andrei Belitsky, Arizona State University
Friday, April 2, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
The spin chain description of evolution equations for higher twist operators was originally discovered in QCD more than a decade ago. In recent years this framework was intensively used to test the AdS/CFT correspondence which allows one to perform calculations at strong coupling in certain gauge theories. We give an overview of these developments with a look on their potential application to QCD.
HighEnergy Physics & RIKEN Theory Seminar
"Identifying the Inert Doublet: A MulitSignature Strategy for a MultiPurpose Model"
Presented by Brooks Thomas, University of Arizona
Wednesday, March 31, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Sally Dawson
The Inert doublet Model (IDM) is one of the simplest possible extensions of the Standard Model, yet it is also one of the most versatile, providing a natural dark matter candidate, applications to neutrino phenomenology and the physics of electroweaksymmetry breaking, and a natural way of addressing the LEP paradox. In this talk, I discuss the prospects for detecting signatures of the IDM at the LHC, and the connection between darkmatter physics and collider phenomenology in this simple yet compelling scenario.
Nuclear Physics & RIKEN Theory Seminar
"Smallx physics with CCFM and problems to tackle at the LHC"
Presented by Emil Avsar, Penn State
Friday, March 26, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
"We give a review of the CCFM (CataniCiafaloniFioraniMarchesini) approach to smallx dynamics and discuss the problems which need to addressed in order to understand the upcoming measurements from the LHC, especially in the forward region
Nuclear Physics & RIKEN Theory Seminar
"Reconstructing jets in heavyion collisions"
Presented by Gregory Soyez, CERN, Switzerland
Friday, March 12, 2010, 11 am
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
Recently, experimental collaborations at RHIC have come out with the first jet measurements in heavyion collisions ever. Because of the busy environment produced in these collisions, this jet reconstruction has long been thought of as unfeasible. In this talk, I will discuss the main ingredients that are used to subtract these large background contributions. I will start with a brief review of what has already been used, then concentrate on potentially new and promising techniques, attempting to improve that mandatory subtraction.
Nuclear Physics & RIKEN Theory Seminar
"Insights on the q_hat problem"
Presented by Simon CaronHuot, Institute for Advanced Study, Princeton
Friday, March 5, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
We study the energy loss by bremsstrahlung for a highenergy jet moving in the quarkgluon plasma. We describe the jet perturbatively but we make no assumption about the interaction strengths in the plasma. We propose an equation giving the radiation rate which generalizes and unify the existing treatments by BaierDokshitzerMuellerPeigneSchiff and Zarkarov (BDMPSZ) and by ArnoldMooreYaffe (AMY). Solving it numerically we can determine approximations which are valid (or not!) under RHIC conditions. This sheds light on the discrepancy regarding the extraction of the ``$\hat{q}$'' parameter by different groups.
Nuclear Physics & RIKEN Theory Seminar
"Bulk viscosity and the applicability of viscous hydrodynamics at RHIC"
Presented by Pasi Huovinen, University of Frankfurt
Friday, February 26, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
Based on comparisons with transport models we had concluded that relativistic viscous hydrodynamics is quite applicable at RHIC. However, when bulk viscosity is included in the description, the applicability can be severely reduced. In this talk I briefly review the comparisons with kinetic theory, propose as a rule of thumb that the entropy production during the evolution has to stay below 20% for hydrodynamic description to be applicable, and show what limits this gives to bulk viscosity and/or the applicability of hydro with bulk viscosity.
Nuclear Physics & RIKEN Theory Seminar
"Transport and Screening in the Magnetized Neutron Star Crusts"
Presented by Sanjay Reddy, Los Alamos National Lab
Friday, February 26, 2010, 11 am
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
After a brief discussion of some generic properties of neutron star crusts and some recent observation that probe this physics, I will discuss a new mechanism by which heat is conducted in the inner crust. In strong magnetic fields, the heat carried by superfluid phonons may become important. In addition, I will show that the modification of the electron screening of the ionion potential at large fields can be important implications for the mechanical structure.
Nuclear Physics & RIKEN Theory Seminar
"Quark pair creation in color electric fields and effects of magnetic fields"
Presented by Naoto Tanji, The University of Tokyo, Japan
Wednesday, February 24, 2010, 11 am
Small Seminar Room, Bldg. 510
Hosted by: Keviin Dusling
The Schwinger mechanism has been studied as a mechanism of matter formation in the context of heavyion collisions. In this talk, I will discuss quark pair creation from a uniform color electric field focusing on its realtime dynamics. I will also show a magnetic field enhances the quark pair creation and induces chiral charge.
Nuclear Physics & RIKEN Theory Seminar
"Stellar Riddles"
Presented by Carlos Bertulani, Texas A&M UniversityCommerce
Friday, February 19, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
ABSTRACT: The most fundamental question in nature is where do we come from, or, put another way, what are we made of? At the heart of this question is the process of nucleosynthesis. I will discuss the challenges in obtaining the nuclear physics input for the Big Bang and stellar evolution. Then I will show how a new generation of theoretical developments and experiments can shed light on the complex nuclear processes that control the evolution of stars and stellar explosions
RIKEN Lunch Seminar/NT
"The QCD phase diagram: Results and challenges"
Presented by Jan Pawlowski, University of Heidelberg, Germany
Thursday, February 18, 2010, 12:30 pm
Physics, Bldg. 510, Rm 2160
Hosted by: Anthony Baltz
I review the progress made in our understanding of the QCD phase diagram within an RG approach to QCD and effective QCD models. In particular this includes a discussion of the confinementdeconfinement phase transition/crossover, the chiral phase transition/crossover, as well as their interrelation.
Nuclear Physics & RIKEN Theory Seminar
"Thermal photons from heavy ion collisions: A spectral function approach"
Presented by Ismail Zahed, SUNY Stony brook
Friday, February 5, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
We analyze the photon rates from a hadronic gas in equilibrium using chiral reduction formulas and a density expansion. The chiral reduction is carried to second order in the pion density which in principal includes all kinetic processes of the type $X\to \pi\gamma$ and $X\to \pi\pi\gamma$. The resulting rates are encoded in the form of vacuum correlation functions which are amenable to experiment. The hadronic rates computed in this work along with the known perturbative QGP rates are integrated over the spacetime evolution of a hydrodynamic model tuned to hadronic observables. The resulting yields are compared to the recent photon and low mass dilepton measurements at the SPS and RHIC. Predictions for the LHC are made.
HighEnergy Physics & RIKEN Theory Seminar
"Revealing RandallSundrum Hidden Valleys"
Presented by Jay Hubisz, Syracuse University
Wednesday, February 3, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Jennifer Kile
I discuss gauge sectors in Randall Sundrum scenarios which are hidden from the standard model through either small gauge coupling, or vanishing quantum numbers. RS gravity provides a bridge between the standard model and the hidden sector, allowing for probes of superweaklycoupled new physics. In particular, a PecceiQuinn axion model is described with novel lowscale interactions.
Nuclear Physics & RIKEN Theory Seminar
"Characterizing the QCD XMatter from the Little Bang"
Presented by Jinfeng Liao, Lawrence Berkeley Natl Laboratory
Friday, January 22, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
ABSTRACT: In this talk, I will report some progresses in characterizing the hot QCD matter (call it an "Xmatter") created in the heavy ion collisions, which is the only experimentally accessible example of a strongly coupled plasma in a nonAbelian gauge theory. I will mainly discuss: (1) how "perfect" this matter is as a fluid e.g. when compared with all other fluids, and in particular what is the proper measure for such a comparison. Furthermore I will also briefly discuss: (2) whether the matter's microscopic degrees of freedom are more chromoelectric or magnetic, and how that characterization is related to QCD confinement; (3) whether the fermions in this matter are more free or more correlated or even bound; (4) what "opaque" pattern this matter has, when imaged by a highly energetic penetrating jet.
Nuclear Physics & RIKEN Theory Seminar
"Some recent results at zero and finite temperature in the Gribov approach to QCD"
Presented by Daniel Zwanziger, New York University
Friday, January 15, 2010, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
I will present an introduction to the Gribov program in QCD and its implementation by a local, renormalizable action. Some recent results on longrange dynamics at zero temperature will be described. The relation of Gribov mass to Linde infrared divergences at finitetemperature and magnetic mass will be reviewed.
Nuclear Physics & RIKEN Theory Seminar
"Kink crystals and chiral spirals in the GrossNeveu phase diagram"
Presented by Gerald Dunne, University of Connecticut (Storrs)
Thursday, December 17, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Robert Pisarski
The GrossNeveu models are 1+1 dimensional models of chiral symmetry breaking, for which the temperature/chemical potential phase diagram has recently been found analytically. There are crystalline condensate phases, with their structure being very different for the GrossNeveu models with discrete and continuous chiral symmetry. I also discuss the relation between the GinzburgLandau expansion and certain integrable models.
HighEnergy Physics & RIKEN Theory Seminar
"Making sense of nonHermitian Hamiltonians"
Presented by Carl Bender, Washington University
Wednesday, December 16, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Sally Dawson
ABSTRACT: The average quantum physicist on the street believes that a quantummechanical Hamiltonian must be Dirac Hermitian (invariant under combined matrix transposition and complex conjugation) in order to guarantee that the energy eigenvalues are real and that time evolution is unitary. However, the Hamiltonian $H=p^2+ix^3$, which is obviously not Dirac Hermitian, has a real positive discrete spectrum and generates unitary time evolution, and thus it defines a fully consistent and physical quantum theory. Evidently, the axiom of Dirac Hermiticity is too restrictive. While $H=p^2+ix^3$ is not Dirac Hermitian, it is PT symmetric; that is, invariant under combined space reflection P and time reversal T. The quantum mechanics defined by a PTsymmetric Hamiltonian is a complex generalization of ordinary quantum mechanics. When quantum mechanics is extended into the complex domain, new kinds of theories having strange and remarkable properties emerge. Some of these properties have recently been verified in laboratory experiments. If one generalizes classical mechanics into the complex domain, the resulting theories have equally remarkable properties.
Nuclear Physics & RIKEN Theory Seminar
"ChernSimons Term Induced Interactions in Holographic QCD"
Presented by Grigoryan Hovhannes, Argonne National Laboratory
Friday, December 11, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
ABSTRACT: We explore the physics associated with the addition of the ChernSimons (CS) term in two holographic models, where the strongly coupled QCD appears to be dual to certain five dimensional (5D) weakly coupled gauge theory. Essentially, we work in the chiral limit of QCD with two flavors, and employ holographic correspondence to compute vertex functions and couplings that are induced by the 5D CS term. In particular, we show that the addition of the 5D CS term allows to reproduce the appropriate chiral anomaly of QCD and much more. As an instructive example, we use one of the CS term induced couplings to provide predictions for the f_1 meson photoproduction
Nuclear Physics & RIKEN Theory Seminar
"Quarkyonic Chiral Spiral"
Presented by Toru Kojo, Brookhaven National Laboratory  RBRC
Friday, December 4, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
In a cold, dense quark matter, there may exist the density region where the system has quark Fermi sea, but also remnant of confinement near the Fermi surface. Such a matter is called quarkyonic matter, which possesses a rigorous foundation in large Nc limit. We argue the chiral properties of quarkyonic matter including nonperturbative effects by gluon propagator supported by GribovZwanziger's analyses. It is shown that nonperturbative selfconsistent equations are reduced to its (1+1) dimensional version, 'tHooft model in finite density. We analyze reduced model by the use of nonAbelian bosonization. We found that chiral spiral emerges with locally violating chiral symmetry but restores it globally. The possible long range to quasilong range order phase transition is also discussed.
HighEnergy Physics & RIKEN Theory Seminar
"Distinguishing Different Types of Dark Matter at the LHC."
Presented by Devin Walker, University of California, Berkeley, LBNL
Wednesday, December 2, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Jennifer Kile
We emphasize the stabilizing symmetry for dark matter does not have to be the commonly used parity symmetry. We therefore examine the potential of the CERN Large Hadron Collider to distinguish models with parity stabilized dark matter from models in which the dark matter is stabilized by other symmetries. We begin this talk by focusing on signatures involving the decay of partners into final states with dark matter and the Standard Model particles. Later we present work distinguishing stabilization symmetries from signals involving metastable partners and dark matter. We show for models without a parity stabilization symmetry the reconstructed invariant mass potentially exhibits double kinematic endpoints due to appearance of one or two DM particles in the final state. For certain scenarios, these endpoints could be measured and the dark matter mass directly reconstructed. This is to be contrasted with the decay chains for parity stabilized models where only one DM candidate appears in the decay chain. We also note that certain decay chain "topologies,'' which are absent for the parity case, generates a "cusp'' in the invariant mass distribution of visible particles. Such generates a distinctive feature which is generally invariant of the various spin configurations. We demonstrate this by presenting novel reconstruction techniques. We illustrate these general ideas with explicit models.
Nuclear Physics & RIKEN Theory Seminar
"Baryonic susceptibilities and Critical behavior in heavy ion collisions"
Presented by Shu Lin, SUNY Stony Brook
Friday, November 20, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin dusling
abstract: In the first part of the talk, I will focus on the baryon contribution to the baryonic susceptibilities. Two types of baryons are identified: one is stringy baryons which are chirally insensitive and have a temperature dependent string tension. Its contribution shows a rise and fall near critical temperature. The other is chirally sensitive nonstringy baryons, through which the dependence on quark chemical potential enters the baryonic density of states. In the second part of the talk, I will talk about the existence of critical impact parameter in heavy ion collisions, modeled by gravitational shock wave collision. I will discuss its dependence on energy and saturation scale and comment on its connection with collision of sourcefree shock waves.
Nuclear Physics & RIKEN Theory Seminar
"Equation of State and Phase Fluctuations near the Chiral Critical Point"
Presented by Joseph Kapusta, University of Minnesota
Friday, November 13, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
The thermodynamics and critical exponents and amplitudes of high temperature and dense matter near the chiral critical point is studied. The parameterized equation of state matches on to that calculated with lattice QCD at zero chemical potential and to the known properties of nuclear matter at zero temperature. The extent to which finite size effects wash out the phase separation near the critical point is determined. The degree to which the critical point acts as an attractor in high energy heavy ion collisions is also investigated.
Nuclear Physics & RIKEN Theory Seminar
"Hydrodynamical behavior and thermalization of a strongly coupled YangMills plasma from AdS/CFT"
Presented by Guillaume Beuf, Brookhaven National Laboratory
Friday, November 6, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
Some data from RHIC suggest that the QGP may be strongly coupled, and behave as a nearly perfect fluid. This observation has triggered many studies based on gauge/string duality. In particular, the hydrodynamical behavior of strongly coupled gauge theories is now undertood thanks to the fluid/gravity correspondence. The understanding of the thermalization process towards a QGP remains one of the main theoretical problems in heavy ion collisions physics. Assuming that this process occurs at strong coupling, it can be adressed using AdS/CFT. After a review of the fluid/gravity correspondence, I will present recents attempts to study thermalization with AdS/CFT. Then I will briefly discuss the problem of the choice of meaningful initial conditions before thermalization.
RIKEN Lunch Seminar
"Lattice simulation of a three dimensional effective theory for SU(2) Yang Mills"
Presented by Dominik Smith, University of Frankfurt, Germany
Thursday, November 5, 2009, 12:30 pm
Physics Dept., Room 2160
Hosted by: Robert Pisarski
It is widely believed that at sufficiently high temperatures or densities, protons and neutrons dissolve into a gas of their constituents, a quark gluon plasma. However, the deconfining phase transition does not pass directly to a gas which can be described as noninteracting particles, but traverses a strongly coupled region, where perturbative methods fail. Also, the usual three dimensional effective theory, EQCD, cannot account for the fluctuations between distinct Z(N) vacua above the phase transition, because EQCD breaks the Z(N) centersymmetry explicitly. As a model for the strongly coupled quark gluon plasma (SQGP), we study an effective theory of SU(2) Wilson Lines, which is constructed in such a way that it respects all of the symmetries of fourdimensional SU(2) pure gauge theory. In this picture, the QGP is a condensate of flux tubes, rather than a gas. Lattice simulations are performed, to investigate whether a "fuzzy bag" term, which is added to the Lagrangian by hand, can induce eigenvalue repulsion and therefore generate nonperturbative fluctuations.
Nuclear Physics & RIKEN Theory Seminar
"Lattice based Equation of State and its effect on the hydrodynamical evolution"
Presented by Pasi Huovinen, University of Frankfurt
Friday, October 30, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
At low temperatures the hadron resonance gas model is expected to give a fair description of thermodynamic quantities even if the lattice QCD calculation leads to significantly different result. In this talk I show that the discrepancies are significantly reduced if we take into account the larger values of quark mass, i.e. larger hadron masses, used in lattice calculations as well as the finite spacing errors. Thus, I propose thatelow the critical temperature, T_c, the physical EoS is close to the hadron resonance gas EoS, and present a parametrization interpolating consistently between hadron resonance gas EoS below and lattice EoS above T_c. In the second part of the talk I show how such an Equation of State affects the evolution of the system and compare it with old calculations done using an Equation of State with a first order phase transition.
Nuclear Physics & RIKEN Theory Seminar
"Integrability of high energy scattering amplitudes in multicolor QCD and N=4 SUSY"
Presented by Lev Lipatov, Petersburg Nuclear Physics Institute (PNPI), Russia
Wednesday, October 28, 2009, 11 am
Small Seminar Room, Bldg. 510
Hosted by: Robert Pisarski
The BFKL aproach based on analitycity, unitarity, renormalizability and crossing symmetry of high energy scattering amplitudes is reviewed. The BKP equations in LLA for the colorless composite states of reggeized gluons in the t'Hooft limit have properties of the Moebius invariance, holomorphic separability, duality and integrability. The BDS ansatz for two gluon production amplitude in N=4 SUSY is shown to be incompatible with the Steinmann relations, which is related to the fact, that this anzatz does not take into account contributions of the Mandelstam cuts. It is shown, that the Hamiltonian for the color octet composite states of several reggeized gluons coincides with the local Hamiltonian of an integrable open Heisenberg spin chain. Analytic properties and an exponentiation hypothesis are enough to calculate production amplitudes in several orders of perturbation theory.
Nuclear Physics & RIKEN Theory Seminar
"Radiative energy loss and v2 spectra for viscous hydro"
Presented by Derek Teaney, Stony Brook University
Friday, October 16, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
This work investigates the consequence of the nonequilibrium phase space distribution on spectra and elliptic flow. We show that the departure from equilibrium on the freezeout surface dominates viscous corrections to $v_2(p_T)$. However, the energy dependence of the departure from equilibrium is not known {\it a priori}. We argue that it is probably not $\propto p_T^2$ as has generally been assumed; and it is generally different for different species. Weaker $p_T$ dependence would lead to straighter $v_2(p_T)$ curves at the same value of viscosity. A species dependent equilibration rate, with baryons equilibrating faster than mesons, can explain "constituent quark scaling" without invoking coalescence models.
Nuclear Physics & RIKEN Theory Seminar
"Recombinant J/Psi production in stronglycoupled quarkgluon plasma"
Presented by Clint Young, Stony Brook University
Friday, October 9, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
The dynamics of charm quarks at the RHIC can be approximated by the Langevin equation, a stochastic differential equation which evolves the distributions towards the thermal predictions. We have extended this approach to charm quarkantiquark pairs, which also experience an attractive interaction measured with lQCD. This model has some agreement with the measured anomalous suppression of J/Psi yields in Au+Au collisions at the RHIC. We now also consider the possibility of recombinant J/Psi production in heavyion collisions, which may increase the J/Psi yields in some collisions significantly. We find that by considering recombinant production, we may achieve agreement with even the latest analysis of R_AA/R_CNM, where the observed suppression is quite smaller than previously thought.
RIKEN Lunch Seminar
"Electromagnetic Form Factors of a Nucleon in Full Lattice QCD"
Presented by Sergey Syritsyn, Massachusetts Institute of Tehnology
Thursday, October 8, 2009, 12:30 pm
Rm 2160; Bldg. 510
Hosted by: Anthony Baltz
I will present a recent highstatistics calculation of nucleon electromagnetic form factors using lattice QCD with 2+1 flavors of dynamical domain wall quarks. This is the first calculation with (almost) chirally symmetric both sea and valence quark actions at pion masses down to m_\pi=300MeV and at lattice spacing as small as a=0.084fm. Using specially tuned techniques to suppress gauge noise and excited state contaminations, we determine the nucleon form factors with a remarkable precision. I will also present the exrapolation of our results using twoflavor chiral perturbation theory and comparison to experiment.
Nuclear Physics & RIKEN Theory Seminar
"Topics in the dynamics of holographic matter"
Presented by Andrei Parnachev, Stony Brook University
Friday, October 2, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Kevin Dusling
We will use methods of gauge/string duality to study properties of strongly interacting matter, including Fermi liquids. Condensed matter theorists are encouraged to attend the seminar.
Nuclear Physics & RIKEN Theory Seminar
"Quantum critical transport in clean graphene"
Presented by Joerg Schmalian, Iowa State University
Friday, September 25, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
We study the role of electronelectron Coulomb interaction in clean graphene and determine the d.c. conductivity, the shear viscosity, and the diamagnetic response of this unique material. Key for an understanding of the Coulomb interaction is the fact that clean, undoped graphene is quantum critical with a marginally irrelevant "fine structure constant". Using standard crossover arguments combined with a quantum kinetic theory, we derive scaling laws, valid near this quantum critical point, that dictate the nontrivial magnetic and charge response of interacting graphene. The most dramatic consequence of this analysis is the anomalous collisiondominated, hydrodynamic transport: the d.c. conductivity of clean graphene is shown to diverge for decreasing temperature (as the square of the logarithm of T), making this material a quantum critical metal. The shear viscosity vanishes as the temperature goes to zero, with an viscosity  entropy density ratio that is close to the behavior expected for a perfect fluid. Finally we show that the viscosity  entropy density ratio is further reduced at the chiral symmetry breaking transition between metallic and insulating behavior.
Nuclear Physics & RIKEN Theory Seminar
"Systematics of High Temperature Perturbation Theory"
Presented by Emil Mottola, Los Alamos National Laboratory
Thursday, August 27, 2009, 12:30 pm
Room 2160, Bldg. 510
Hosted by: Gregory Soyez
The systematics and reorganization of the perturbative loop expansion in high temperature gauge theories is investigated. In addition to infrared divergences in the bare loop expansion with massless fermions, further evidence for the necessity of a systematic restructuring of perturbation theory comes from the explicit gauge parameter dependence of the fermion damping rate at both one and twoloops. The calculation of the twoloop fermion selfenergy in QED shows that the leading terms in the high temperature expansion arise from an explicit hardsoft factorization pattern, in which one of the loop integrals is hard (p ~ T), nested inside a second loop integral which is soft (p ~ eT). There are no hardhard contributions to the twoloop selfenergy at leading order at high T. This hardsoft factorization pattern is necessary for the resummation over multiple loops to coincide with the oneloop selfenergy calculated with HTL dressed propagators and vertices, and to yield the complete nexttoleading order correction to the selfenergy at scales ~eT, which is both infrared finite and gauge invariant. The gauge invariant effective action corresponding to this resummation and possible extensions of the resummation program to softer processes not captured in the HTL approach will also be discussed.
Nuclear Physics & RIKEN Theory Seminar
"AdS/CFT and Heavy Ion Collisions"
Presented by Edmond Iancu, Saclay, France
Friday, August 21, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
After briefly recalling the experimental results at RHIC which support the picture of a stronglycoupled, deconfined QCD matter, I discuss applications of the string theory, via the AdS/CFT correspondence, to the study of such a form of matter. I emphasize some striking consequences of the strongcoupling scenario, like the absence of jets, the strong suppression of the parton distributions at large values of Bjorkenx, and a novel mechanism (the mediuminduced parton branching) for the energy loss and the momentum broadening of a hard probe. I discuss a recent proposal for a lattice measurement which should clarify whether the quarkgluon plasma is effectively stronglycoupled or not in the temperature range of interest for RHIC and LHC.
Nuclear Physics & RIKEN Theory Seminar
"Cold Relativistic Superfluids: Transport Phenomena and Applications"
Presented by Cristina Manuel, Instituto de Ciencias del Espacio (CSIC)
Friday, August 14, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
Superfluidity occurs in cold systems after the appearance of a quantum condensate that breaks spontaneously a global U(1) symmetry. We review the basic features of relativistic superfluid hydrodynamics, paying special attention to colorflavor locked quark matter. At very low temperatures, transport phenomena is dominated by the contribution of the superfluid phonon, a Goldstone mode of the system. Using low energy effective field theory techniques, one can estimate relaxation time scales and the four viscosity coefficients of the superfluid. We also show how to construct a transport equation for the phonon using a gravity analogue model. Finally, we discuss how the knowledge of all the dissipative processes is needed in astrophysical scenarios for the study of rotational properties of compact stars
Nuclear Physics & RIKEN Theory Seminar
"Applications of AdS/CFT in DIS"
Presented by Anastasios Taliotis, Ohio State University
Friday, July 17, 2009, 11 am
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
We calculate the total cross section for deep inelastic scattering (DIS) on a nucleus at high energy for a strongly coupled N = 4 super YangMills theory using AdS/CFT correspondence. In analogy to the small coupling case we argue that at high energy the total DIS cross section is related to the expectation value of the Wilson loop formed by the quarkantiquark dipole. We model the nucleus by a metric of a shock wave in AdS5. We then calculate the expectation value of the Wilson loop by finding the extrema of the NambuGoto action for an open string attached to the quark and antiquark lines of the loop in the background of an AdS5 shock wave. We find three extrema of the NambuGoto action: the string coordinates at the extrema are complexvalued and are given by three different branches of the solution of a cubic equation. The physically meaningful solutions for the total DIS cross section are given either by the only branch with a purely imaginary string coordinate in the bulk or by a superposition of the two other branches. For both solutions we obtain the forward scattering amplitude N for the quark dipolenucleus scattering. We study the onset of unitarity with increasing centerofmass energy and transverse size of the dipole: we observe that for both solutions the saturation scale, while energydependent at lower energies, at very high energy becomes independent of energy/Bjorkenx. The saturation scale depends very strongly on the atomic number of the nucleus as Qs ~ A^1/3.
Nuclear Physics & RIKEN Theory Seminar
"Smallx Evolution of Structure Functions in the NexttoLeading Order"
Presented by Giovanni Chirilli, Old Dominion University/Jefferson Lab
Friday, June 26, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
The highenergy behavior of amplitudes in gauge theories can be reformulated in terms of the evolution of Wilsonline operators. In the leading order this evolution is governed by the nonlinear BalitskyKovchegov (BK) equation. The NLO corrections define the scale of the runningcoupling constant in the BK equation and in QCD, its kernel has both conformal and nonconformal parts. To separate the conformally invariant effects from the runningcoupling effects, we calculate the NLO evolution of the color dipoles in the conformal N = 4 SYM theory, then we define the "composite dipole operator" with the rapidity cutoff preserving conformal invariance, and the resulting Mobius invariant kernel for this operator agrees with the forward NLO BFKL calculation. In QCD, the NLO kernel for the composite operators resolves in a sum of the conformal part and the runningcoupling part.
Nuclear Physics & RIKEN Theory Seminar
"On heavy meson dissociation in QCD matter: a comparison of Debye screening and multiple scattering"
Presented by Bin Wu, Peking University
Friday, June 19, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
In this talk, I will report what we find about the criterion for fast moving heavy mesons in an infinite hot quarkgluon plasma by comparing Debye screening and multiple scattering. And I will also talk about the dissociation of mesons due to multiple scattering in cold and hot QCD matter.
Nuclear Physics & RIKEN Theory Seminar
"Jet evolution in stable and unstable nonAbelian plasmas"
Presented by Bjoern Schenke, McGill University, Canada
Friday, June 12, 2009, 1 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
I present results for elastic energy loss and momentum broadening of high momentum partons in hot and dense nonAbelian plasmas, obtained by solving the coupled system of WongYangMills equations on a lattice in real time. Including hard elastic collisions among the particles we find cutoff independent results for collisional energy loss and momentum broadening in stable plasmas. Furthermore, I present the effects of instabilities on jetbroadening in anisotropic plasmas. In this case the partons experience asymmetric broadening in the extended domains of growing color fields.
Nuclear Physics & RIKEN Theory Seminar
"Eta/s of a relativistic hadron gas from a hadronic cascade"
Presented by Nasser Demir, Duke University
Friday, June 5, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
Ultrarelativistic heavyion collisions at the Brookhaven National Laboratory Relativistic Heavy Ion Collider (RHIC) are thought to have produced a state of matter called the quarkgluon plasma, characterized by a very small shearviscosity to entropydensity ratio eta/s, near the lower bound predicted for that quantity by the KSS bound. As the produced matter expands and cools, it evolves through a phase described by a hadron gas with rapidly increasing eta/s. We present a calculation of eta/s as a function of temperature utilizing the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model, and investigate the effect of the separation of thermal vs chemical freezeout on eta/s in our calculation. Our results find that eta/s in the hadronic phase is rather large, and the oftdiscussed viscous hydrodynamics calculations suggest a strong temperature dependence of eta/s, especially as it crosses T_c in a heavy ion reaction.
Nuclear Physics & RIKEN Theory Seminar
"Spin  How much do we know?"
Presented by Jianwei Qiu, Department of Physics and Astronomy, Iowa State University
Friday, May 1, 2009, 3:30 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
Protons and neutrons have spin 1/2 and are known to be the building blocks of matter. They are the bound states of quarks and gluons, whose dynamics is best described by Quantum Chromodynamics (QCD). I will briefly review how to express the proton spin in terms of the degrees of freedom of quarks and gluons. It is a challenge to directly measure individual contribution of quarks and gluons to the proton spin. I will show that high energy collisions with measured polarization offer many new opportunities to probe QCD dynamics that could not be reached by spinaveraged collisions. A successful spin program could shed the light on how QCD encompasses both protons and neutrons and the quark and gluon degrees of freedom that make them up.
HighEnergy Physics & RIKEN Theory Seminar
"Electromagnetic NeutralMeson Decays on the Lattice"
Presented by Saul Cohen, Jefferson Lab
Wednesday, April 29, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Taku Izubuchi
I present a study of twophoton decays of light mesons, focusing on the neutral pion decay. This important process highlights the effects of the axial anomaly in QCD but has been little studied on the lattice. By applying the LehmannSymanzikZimmermann (LSZ) reduction formula, we reconstruct the electromagnetic matrix elements from three point vectorvector Green functions calculated on fullQCD lattices.
Nuclear Physics & RIKEN Theory Seminar
"Magnetic Moment of the Delta and Omega baryons on the lattice"
Presented by Christopher Aubin, College of William & Mary
Friday, April 17, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Taku Izubuchi
I will discuss a lattice calculation of the magnetic moments of the Delta and Omega baryons using a background electromagnetic field technique with 2+1 flavors of anisotropic Clover fermions, on lattices generated by the Hadron Spectrum Collaboration. I will go into some detail of the systematics associated with using background EM fields on the lattice, as well as issues in extending the method to calculate higher moments.
HighEnergy Physics & RIKEN Theory Seminar
"Nearly Conformal Gauge Theories and Compositeness at the LHC"
Presented by Julius Kuti, University of California, San Diego
Wednesday, April 8, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Taku Izubuchi
I will review recent progress on the nonperturbative studies of nearly conformal gauge theories which provide a mechanism to replace the conventional Higgs sector of the standard model. The conformal window is identified in these theories in different flavor and color representations by establishing the chirally broken phase and the fixed point of the running gauge coupling. Reliable results are beginning to emerge from lattice calculations by matching to low energy Goldstone dynamics and random matrix theory. The running coupling is determined from the renormalization behavior of Wilson loops and from the Schrodinger functional. The challenges and difficulties of the calculations, unlike the ones in QCD, will be reviewed as well.
Joint HET/RIKEN/YITP Seminar
"Fundamental Physics from the Sky"
Presented by Stefano Profumo, SCIPP, University of California, Santa Cruz
Wednesday, April 1, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Hooman Davoudiasl
Can we learn about New Physics with astronomical and astroparticle data? Understanding how this is possible is key to unraveling one of the most pressing mysteries at the interface of cosmology and particle physics: the fundamental nature of dark matter. Rapid progress may be within grasp in the context of an approach which combines information from highenergy particle physics with cosmicray and traditional astronomical data. I discuss recent puzzling data on cosmicray electrons and positrons and their interpretation. I show how the Fermi Space Telescope will soon shed light on those data as well as potentially on several dark matter particle properties. I then introduce a novel approach to particle dark matter searches based on the complementarity of astronomical observations across the electromagnetic spectrum, from radio to Xray and to gammaray frequencies.
Nuclear Physics & RIKEN Theory Seminar
"On the behavior of largeN QCD with nonzero chemical potentials"
Presented by Barak Bringoltz, University of Washington
Friday, March 27, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
I will discuss the way QCD behaves at zero temperature and nonzero density in its largeN limit. I will first present, and resolve, certain subtle confusions in the literature and show that while quarks are not backreacting on the gauge fields at largeN, they are certainly not "quenched" in any sense. I will then describe a recent calculation in which the largeN ground state of twodimensional QCD was found for arbitrary values of the baryon number, volume, quark mass and lattice spacing. I will discuss the resulting phase diagram that contains a helical crystal of baryons. If time allows I will remark on the implications of this phase diagram on the validity of lattice studies that rely on "EguchiKawai" volume independence, and on the properties of the QCD "sign problem".
Nuclear Physics & RIKEN Theory Seminar
"Formation of horizon and equilibration of QGP"
Presented by Shu Lin, Stony Brook University
Friday, March 20, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
I will start with a short review on various probes to Quark Gluon Plasma studied by AdS/CFT. The study of the probe typically amounts to solving linearized Einstein equation. The more challenging task is to understand the equilibration of matter and formation of QGP. I will talk about a specific gravitational collapse model, which is dual to the thermalization of gauge field on the boundary. We found the spectral density of stress energy tensor differs from its thermal counterpart by some general oscillation. I will also talk about the recent works on entropy estimation in heavy ion collision from gravitational shock wave collision. We found the existence of critical impact parameter, beyond which no horizon can form. In the dual field theory, it means matter produced in the collision cannot thermalize.
Nuclear Physics & RIKEN Theory Seminar
"Universality in Early Flow at RHIC"
Presented by Joshua Vredevoogd, Michigan State University
Friday, March 13, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
It was long thought that early thermalization of the hot matter created in high energy heavy ion collisions was required to simultaneously explain the large elliptic flow and the source sizes. We will show instead that for any description of the matter with a traceless stressenergy tensor  fields or particles, equilibrated or not  early flow is generated at the same level. This significantly lessens the uncertainty in modeling the early stages of the collision.
HighEnergy Physics & RIKEN Theory Seminar
"Electroweak precision physics with W and Z bosons"
Presented by Doreen Wackeroth, SUNY at Buffalo
Wednesday, March 11, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Christian Sturm
The production of W and Z bosons is one of the best understood and most precisely studied processes. However, in view of the increased experimental precision at the Tevatron and the LHC, the available calculations and tools that provide predictions for W and Z boson observables may not be sufficient. I will give an overview of the theory status and recent developments with special emphasis on the treatment of higherorder corrections.
Nuclear Physics & RIKEN Theory Seminar
"Saturation and Confinement: Pomeron, Odderon, and AdS/CFT"
Presented by ChungI Tan, Brown University
Friday, March 6, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Dima Kharzeev
In 1/Nc expansion, analyticity and crossing lead to crossing even and odd (C = ±1) vacuum exchanges at highenergy, the Pomeron and the Odderon. We discuss how, using String/Gauge duality, these can be identified with the closed string Reggeized graviton and the antisymmetric KalbRamond fields in AdS background. With confinement, these Regge singularities interpolate with glueball states. We also discuss unitarization and saturation based on eikonal sum in AdS.
Nuclear Physics & RIKEN Theory Seminar
"The Response of a Thermal QGP to Radiating Hard Partons"
Presented by Bryon Neufeld, Duke University
Friday, February 27, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
I calculate the total energy deposited into the medium per unit length by fast partons traversing a quarkgluon plasma. The medium excitation due to collisions is taken to be given by the well known expression for the collisional drag force. The radiative energy loss of the parton contributes to the energy deposition because each radiated gluon acts as an additional source of collisional energy loss in the medium. I derive a differential equation which governs how the spectrum of radiated gluons is modified when this energy loss is taken into account. This modified spectrum is then used to calculate the differential energy loss due to the interactions of radiated gluons with the medium. The final result for the energy deposited into the medium per unit length, which is a sum of the primary and the secondary contributions, is then treated as the coefficient of a local hydrodynamic source term. Numerical results are presented for the medium response for the case of two fast, backtoback partons created in an initial hard interaction.
Nuclear Physics & RIKEN Theory Seminar
"How viscosity affects quarkonium states in the QGP"
Presented by Adrian Dumitru, Baruch College
Friday, February 20, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
In an expanding plasma, nonzero shear viscosity implies an anisotropic momentum distribution of particles in a fluid cell. This leads to anisotropic screening of static electric fields. I present a simple model for the static potential between infinitely heavy fundamental charges which includes the Coulomb as well as the string force and is easily extended to anisotropic plasmas. Finally, I show the binding energies of 1S/1P charmonium and bottomonium states and the polarization of 1P bb_bar states in the deconfined phase obtained from this potential.
Nuclear Physics & RIKEN Theory Seminar
"LHC searches: what role for QCD"
Presented by Gavin Salam, University of Paris VI, France
Friday, February 13, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
This talk considers some of the ways in which QCD might play a role in searches for new physics at the LHC. It examines the question of the reliable estimation of backgrounds, as well as that of how QCD can guide us in designing better tools to extract any new physics signals from the background.
Nuclear Physics & RIKEN Theory Seminar
"Quarkonia in Medium and in HeavyIon Collisions"
Presented by Ralf Friedrich Rapp, Texas A&M University
Friday, February 6, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
The properties of quarkonia in equilibrium QCD matter are studied and put into context with observables in ultrarelativistic heavyion collisions at SPS, RHIC and LHC. In the first part of the talk we focus on applications of potential models utilizing input from heavyquark free energies computed in latticeQCD. Applications to Euclidean correlation functions (independently computed in lattice QCD) currently exhibit a degeneracy of scenarios with small and large J/psi dissociation temperatures, due to an interplay of inmedium binding energies and heavyquark masses. We also elaborate on the impact of color screening on quarkonium dissociation mechanisms in the QuarkGLuon Plasma. In the second part of the talk we address the current status of the phenomenology at SPS and RHIC, in particular the competition between dissociation and regeneration mechanisms and which observables might be most promising for discriminating them (including the LHC).
Nuclear Physics & RIKEN Theory Seminar
"Solitonic ground states in (color) superconductivity"
Presented by Dominik Nickel, MIT
Tuesday, January 20, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Robert Pisarski
Inhomogeneous ground states due to imbalanced Fermi surfaces have been discussed in various contexts. The investigation of these socalled LOFF states has usually been constrained to simple ansaetze or the GinzburgLandau approximation. By the example of an NJLtype model I discuss new features when going beyond the GinzburgLandau approximation, in particular the emergence of a soliton lattice. Concentrating on onedimensional periodic structures in 3+1 dimensions I present properties of the ground state and contrast them with known results. I also give an account on the weakcoupling limit.
Nuclear Physics & RIKEN Theory Seminar
"A theory of jet shapes and cross sections: from hadrons to nuclei"
Presented by Ivan Vitev, Los Alamos National Laboratory
Friday, January 16, 2009, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
For jets, with great power comes great opportunity. The unprecedented center of mass energies available at the LHC open new windows on the QGP: we demonstrate that jet shape and jet cross section measurements become feasible as a new, differential and accurate test of the underlying QCD theory. We present a first step in understanding these shapes and cross sections in heavy ion reactions. Our approach allows for detailed simulations of the experimental acceptance/cuts that help isolate jets in such highmultiplicity environment. It is demonstrated for the first time that the pattern of stimulated gluon emission can be correlated with a variable quenching of the jet rates and provide an approximately model independent approach to determining the characteristics of the mediuminduced bremsstrahlung spectrum. Surprisingly, in realistic simulations of parton propagation through the QGP we find a minimal increase in the mean jet radius even for large jet attenuation. Jet broadening is manifest in the tails of the energy distribution away from the jet axis and its quantification requires high statistics measurements that will be possible at the LHC.
Nuclear Physics & RIKEN Theory Seminar
"Are GPDs and TMDs related?"
Presented by Marc Schlegel, Jefferson Lab
Friday, December 19, 2008, 11 am
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
Generalized Parton Distributions (GPDs) and Transverse Momentum Dependent Parton Distributions (TMDs) are a priori different classes of parton distributions. While GPDs appear in the description of hard exclusive processes, TMDs are important for semiinclusive processes like DrellYan or semiinclusive DIS. Nevertheless, nontrivial relations between GPDs and TMDs have been suggested recently. In this talk the status of these relations are discussed and some new ideas on this matter are presented.
Nuclear Physics & RIKEN Theory Seminar
"The role of monopoles in a gluon plasma"
Presented by Claudia Ratti, Stony Brook University
Friday, December 12, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
We study the role of magnetic monopoles at high enough temperature $T>2T_c$, when they can be considered heavy, rare objects embedded into matter consisting mostly of the usual "electric" quasiparticles, quarks and gluons. We find that, while this process hardly influences thermodynamic quantities, it produces a large transport cross section, keeping viscosity small enough for hydrodynamics to work at LHC.
Nuclear Physics & RIKEN Theory Seminar
"From Quarks and Gluons to Hadrons: A Study of the QCD Phase Boundary"
Presented by Jens Braun, TRIUMF Canada
Friday, December 5, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
I discuss chiral symmetry breaking in QCD with its underlying mechanisms in terms of quarks and gluons and show the chiral phase boundary in the plane of temperature and number of (massless) quark flavors obtained from a functional renormalization group approach. Moreover, the dependence of the phase transition temperature on the quark chemical potential is discussed. The subject of the last part of the talk is the deconfinement phase transition in YangMills theory. The results obtained from a functional renormalization group approach for the orderparameter potential, namely the Polyakovloop potential, are shown.
Nuclear Physics & RIKEN Theory Seminar
"Bulk, shear and heavy ion collisions"
Presented by Pasi Huovinen, Purdue University
Friday, November 21, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
In this talk I will concentrate on entropy production in heavy ion collisions due to shear and bulk viscosities. I will review the basics of causal viscous hydrodynamics and estimate the validity of the hydrodynamical description by comparing with transport theory calculations and by estimating the amount of produced entropy. I will also assess the relative contributions of shear and bulk viscosities to the evolution.
Joint HET/RIKEN/YITP Seminar
"From Vortices in Superconductivity to Quark Confinement"
Presented by Mikhail Shifman, University of Minnesota
Wednesday, November 19, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Hooman Davoudiasl
Supersymmetry, born in the early 1970s, is a very rich theory which is supposed to describe the widest range of natural phenomena. Although it has not yet been discovered experimentally, it proved to be a powerful tool in Quantum Chromodynamics (QCD)  the theory of hadrons  and strongly coupled gauge theories at large. Efforts aimed at solving various aspects of QCD basing on supersymmetry and stringinspired ideas bring fruits. In a remarkable entanglement, theoretical constructions of the 1970s and 1990s combine with today's ideas to provide new insights and a deeper understanding.
Nuclear Physics & RIKEN Theory Seminar
"HighEnergy Gluon Bremsstrahlung in a Finite, Expanding Medium"
Presented by Peter Arnold, University of Virginia
Friday, November 14, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
Highenergy gluon bremsstrahlung in a QCD plasma is suppressed by the LandauPomeranchukMigdal (LPM) effect. At very high energies E, various folks have analyzed the problem analytically in the limit that log(E) is treated as large. In this talk, I will give a qualitative discussion of the LPM effect and the equations which describe it. Then I will present new results that magically simplify previous formulas derived for the bremsstrahlung gluon emission spectrum in the large log(E) limit. I will also discuss the interplay between two different approximations that have been used to study energy loss in the large log(E) limit, known as the "harmonic oscillator" approximation and the opacity expansion.
Nuclear Physics & RIKEN Theory Seminar
"Some cosmological LHC and other physics aspects of new heavy colored particles carrying an extra color' with 10 eV 10 KeV scale"
Presented by Prof. Shmuel Nussinov, Tel Aviv University
Thursday, November 13, 2008, 12:30 pm
Room 2160, Bldg. 510
Hosted by: Gregory Soyez
Nuclear Physics & RIKEN Theory Seminar
"Noise and quarkonia transport in AdS5"
Presented by Derek Teaney, Stony Brook University
Friday, October 31, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
I first compute the drag and diffusion rates of heavy mesons in AdS_5. Subsequently I show how thermal noise arises in the context of gauge gravity duality. I use this identification to recompute several results previously found in the diffusion of heavy quarks. However, I extend these results to compute the photon emission rate from a fast quark in AdS_5 and contrast this rate with perturbation theory. Finally I conclude by indicating how an appealing picture of thermal noise which arises can be used to calculate the diffusion of mesons whose mass is of order the temperature.
Nuclear Physics & RIKEN Theory Seminar
"NonMach Conical Dijet Correlations in AdS/CFT"
Presented by Jorge Noronha, Columbia University
Friday, October 10, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Gregory Soyez
The reported observation of Mach conelike correlations between tagged (near side) jets fragments and away side associated moderate pT < 4 GeV/c hadrons has generated a lot of interest because it may provide further evidence for fast relaxation times and the near perfect fluid property of the strongly QuarkGluon Plasma (sQGP) produced in Au+Au reactions at RHIC. In this talk, we show that far zone Mach and Diffusion wake ``holograms'' produced by supersonic strings in AdS/CFT do not lead to observable conical angular correlations in the strict $N_c\to\infty$ supergravity limit if CooperFrye hadronization is assumed. However, a special nonequilibrium ``Neck'' zone close to the heavy quark is shown to give rise to an apparent sonic boom azimuthal angle distribution that however does not obey Mach's law. The observation of nonMach conical correlations associated with tagged heavy quark jets would provide additional support for novel nonperturbative dynamics as suggested by the AdS/CFT string phenomenology.
Nuclear Physics & RIKEN Theory Seminar
"Target mass corrections and beyond"
Presented by Alberto Accardi, Jefferson Lab
Friday, September 26, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Harmen Warringa
I will examine the uncertainty of perturbative QCD factorization for hadron structure functions in deep inelastic scattering at a large value of the Bjorken variable xB. The focus will be on Target Mass Corrections (TMC) and Jet Mass Corrections (JMC) in the framework of collinear factorization. The proposed corrections are needed in QCD global fits of parton distribution functions at largex, lowQ^2 for enlarging the data set and improving the accuracy. This is especially true for polarized targets, where the bulk of the data lies in such a region of phase space. I will discuss some preliminary results including TMC for unpolarized structure functions.
Nuclear Physics & RIKEN Theory Seminar
"Issues about partonic transverse momentum distributions"
Presented by Alessandro Bacchetta, Jefferson Lab
Friday, September 19, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Harmen Warringa
Partonic transverse momentum distributions (TMDs) expose new aspects of the structure of the nucleon, not accessible by collinear parton distribution functions. They can be measured in semiinclusive hard scattering experiments and require the extension of the theoretical ideas usually employed to collinear distribution functions. I will review some topics relevant for the theory and phenomenology of TMDs, focusing on a few crucial examples.
Nuclear Physics & RIKEN Theory Seminar
"First results from full jetreconstruction in heavyion collisions at RHIC"
Presented by Joern Putschke, Yale University
Friday, September 5, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Harmen Warringa
Measurements of inclusive hadron suppression and dihadron azimuthal correlations in ultrarelativistic nuclear collisions have provided important insights into jet quenching in hot QCD matter, but are limited in their sensitivity due to wellknown biases. Complete jet reconstruction in heavyion collisions would provide a direct measurement of the energy of the scattered parton before energy loss, alleviating such biases and allowing a measurement of the energy loss probability distribution necessary to extract properties of the medium in a modelindependent way from hard probes. In this talk the first measurement of the inclusive jet spectrum and the fragmentation function of fully reconstructed jets in 200 GeV heavy ion collisions will be presented. The fragmentation function as well as the jet spectra in heavy ion collisions will be presented and discussed with respect to p+p reference measurements.
Nuclear Physics & RIKEN Theory Seminar
"Optimising jet finding in pp and AA collisions"
Presented by Gregory Soyez, Brookhaven National Laboratory
Friday, August 15, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Harmen Warringa
After a generic introduction covering the recent important developments in jet physics and the need to use infraredandcollinearsafe tools for future analysis, I will try to answer the question "what is the optimal jet algorithm for hadronic collisions?". I will show that this varies from process to process and from scale to scale, suggesting flexibility for LHC studies. Then, still in the context of finding an optimal jet finder, I will discuss practical methods to subtract soft background like pileup in the case of pp collisions or the underlying event in the case of heavyion collisions.
Nuclear Physics & RIKEN Theory Seminar
"Is energymomentum conservation masquerading as more interesting physics? How different are p+p and Au+Au collisions, really?"
Presented by Michael Lisa, Ohio State University
Friday, August 8, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Harmen Warringa
Transverse momentum distributions and femtoscopic measurements in ultrarelativstic heavy ion collisions carry considerable information about the dynamics of the hot system produced. Direct comparison with the same spectra from p+p collisions has proven invaluable to identify novel features associated with the larger system, in particular, the ``jet quenching'' at high momentum and apparently much stronger collective flow dominating the spectral shape at low momentum. I will discuss possible hazards of ignoring conservation laws in the comparison of high and lowmultiplicity final states. I will argue that the effects of energy and momentum conservation actually dominate many of the observed systematics, and that p+p collisions may be much more similar to heavy ion collisions than generally thought. Much of the material for this talk may be found at: Z. Chajecki and M.A. Lisa arXiv:0803.0022 [nuclth] Z. Chajecki and M.A. Lisa arXiv:0807.3569 [nuclth]
Nuclear Physics & RIKEN Theory Seminar
"sChannel Unitarity Experimental Signatures and Their Implications"
Presented by Uri Maor, Tel Aviv University, Israel
Friday, June 27, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Harmen Warringa
Recent calculations of soft scattering in exceedingly high energies are summarized with special emphasize on the role of unitarity and the consequent survival probabilities of hard diffractive LRG processes. Updated theoretical concepts and models are compared aiming to assess their validity in expectation for HERA and AUGER first generation results. Survival probabilities for exclusive central diffractive Higgs LHC production are quoted.
Nuclear Physics & RIKEN Theory Seminar
"Gluinos condensing at the CCNI"
Presented by Joel Giedt, Rensselaer Polytechnic Institute
Friday, June 20, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Harmen Warringa
We discuss the status of gluino condensation and other results using RPI's BlueGene/L cluster, part of the CCNI supercomputing complex (world's 7th most powerful). This Domain Wall Fermion computation will give, for the first time, continuum extrapolations of important quantities such as the condensate and string tension.
Nuclear Physics & RIKEN Theory Seminar
"Spectral analysis of gluonic pole matrix elements for fragmentation"
Presented by Asmita Mukherjee, Indian Institute of Technology Bombay
Friday, June 13, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Werner Vogelsang
The nonvanishing of gluonic pole matrix elements can explain the appearance of single spin asymmetries in highenergy scattering processes. We use a spectator model approach to investigate the spectral properties of quarkquarkgluon correlators and use this to study gluonic pole matrix elements. Such matrix elements appear in principle both for distribution functions (such as Sivers function) and fragmentation functions such as Collins function. We find that for a large class of spectator models, the contribution of gluonic pole matrix element in fragmentation functions vanishes. This outcome is important in the study of universality for fragmentation functions and confirms findings using a different approach.
Nuclear Physics & RIKEN Theory Seminar
"Perfect Fluids: From Nano to Terra (Kelvin)"
Presented by Thomas Schaefer, North Carolina State University
Friday, June 6, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Harmen Warringa
It has been argued that the quark gluon plasma produced at RHIC is a ``perfect fluid'', i.e. that it saturates a proposed lower bound on the viscositytoentropy density ratio. In order to better understand what this means, and to get a feeling for how reliably one can extract the viscosity of a strongly coupled quantum fluid, I have studied the thermodynamic and transport properties of cold trapped fermions. In this talk I will focus, in particualr, on transport in the ``unitarity limit'', that is the limit in which the low energy swave cross section between the atoms saturates the quantum mechanical unitarity bound.
Nuclear Physics & RIKEN Theory Seminar
"Questioning hydro at RHIC: Is it QCD all the way down?"
Presented by Tom Trainor, University of Washington
Friday, May 30, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Harmen Warringa
Conventional analysis of RHIC data separates spectrum and correlation structure into three regimes: hard parton scattering and fragmentation described by pQCD (large pt), soft hadron production from a thermalized "partonic" medium described by hydro (small pt), and coalescence/recombination of "constituent quarks" from the flowing medium and from the parton fragment system (intermediate pt). Support for that picture is derived from the "blastwave" spectrum model, "elliptic flow" measure v2 and "jet quenching" measure RAA. I review the standard conventions in the context of a "twocomponent" (soft + hard) model of spectra and correlations applied consistently over the full range of measured pt from 0.1 to 12 GeV/c. I relate the hard component, deduced from pp spectra, to LEP fragmentation functions and the soft component to longitudinal nucleon fragmentation. I recast the RAA measure to a true ratio comparison of spectrum hard components (soft components are excluded). From v2(pt) data I reconstruct for the first time the spectra of identified "flowing" particles (quadrupole component) and show that the quadrupole is apparently unrelated to dramatic features of parton energyloss systematics recently observed in spectra and angular correlations. I conclude that the quadrupole component is a small fraction of the total system and may represent a novel QCD radiation phenomenon. Hydrodynamic models and thermal equilibrium appear to be inconsistent with accurate descriptions of data.
Nuclear Physics & RIKEN Theory Seminar
"Disordered BoseEinstein Condensates: Probing Quantum and Density Fluctuations in Superfluidtoinsulator transitions"
Presented by Dr. Yong Chen, Purdue University
Friday, May 23, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Harmen Warringa
Atomic BoseEinstein condensates (BEC) provide excellent model systems to study quantum matter, with relevance in diverse fields ranging from condensed matter physics to cosmology. I will describe our recent experiments on a BEC subject to a controllable disordered potential, which can drive the BEC from a superfluid to an insulator. The disorder introduces quantum and/or density fluctuations to the BEC and we have studied how these fluctuations evolve during the expansion of the BEC. Ref: Yong P. Chen et al., Phys. Rev. A, 77, 033632 (2008)
Nuclear Physics & RIKEN Theory Seminar
"Prompt photons at RHIC: a multipurpose observable"
Presented by Francois Arleo, CERN
Friday, May 2, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Harmen Warringa
In this talk I will present two interesting phenomenological aspects of prompt photon production in hadronic collisions at RHIC and LHC. The possibility to measure the nuclear modification of the gluon distribution at small x, G^A(x)/G^p(x), is first discussed. The production of isolated photons in pA (or dA) collisions turns out to be a promising channel which allows for a reliable extraction of the gluon density and the structure function in a nucleus over that in a proton. In the section part, I will then explore how double inclusive photonhadron production in pp scattering can be used as a tool to constrain the fragmentation functions into hadrons, as well as their possible modifications in AA collisions.
Nuclear Physics & RIKEN Theory Seminar
"On the accelerating string and finite extent plasma energy loss"
Presented by Bowen Xiao, Columbia University
Friday, April 18, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Harmen Warringa
In this talk, I would like to start with the introduction to the exact accelerating string solution of a heavy quarkantiquark pair in $AdS_5$ space. On the accelerating string, there is a particular scale which separates the radiation and the heavy quark. This scale is explicitly shown to be an event horizon in the proper frame of the heavy quark. Furthermore, I will describe a new correspondence, which relates the horizon in $AdS_5$ space on the gravity theory side to the Unruh temperature in Minkowski space on the field theory side of the AdS/CFT correspondence. $p_{\perp}$broadening and $p_{L}$broadening of the heavy quark due to radiation are computed using the AdS/CFT correspondence. In the end, using AdS/CFT correspondence and the accelerating string solution, heavy quark energy loss in finite extent plasma is discussed.
Nuclear Physics & RIKEN Theory Seminar
"Quantum Monte Carlo Calculations of Light Nuclei"
Presented by Robert Wiringa, Argonne National Laboratory
Friday, April 4, 2008, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Harmen Warringa
Accurate calculations of the structure of light nuclei, starting from "bare" twonucleon interactions that fit NN scattering data, have become feasible over the last decade using quantum Monte Carlo methods. Threenucleon interactions and twobody electroweak current operators are important additional inputs. Properties we can study include binding and excitation energies, relative stability, one and twonucleon densities in configuration and momentum space, electromagnetic moments and electroweak transitions. We are also developing the tools for nucleonnucleus scattering and electroweak capture reactions. In these studies we can see that nuclear structure really does arise from these complicated "bare" nuclear forces. Finally, we can use these tools to study more speculative issues, such as how nuclear structure evolves with the complexity of the nuclear forces, or how it might differ with changes in fundamental constants.
Nuclear Physics & RIKEN Theory Seminar
"Early Time Dynamics in Heavy Ion Collisions from AdS/CFT Correspondence"
Presented by Yuri Kovchegov, Ohio State University
Friday, December 14, 2007, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Harmen Warringa
We study the matter produced in heavy ion collisions assuming that this matter is strongly interacting and employing AdS/CFT correspondence to investigate its dynamics. At late proper times tau we show that Bjorken hydrodynamics solution, obtained recently by Janik and Peschanski using gaugegravity duality, can be singled out by simply requiring that the metric tensor is a real and singlevalued function of the coordinates everywhere in the bulk, without imposing any constraints on the curvature invariant. At early proper times we use similar strategy to show that the energy density epsilon approaches a constant as tau > 0. We therefore demonstrate that the strong coupling dynamics incorporates the isotropization transition in heavy ion collisions. By matching our earlytime regime with the latetime one of Janik and Peschanski we estimate the isotropization time at RHIC to be approximately 0.3 fm/c, in good agreement with results of hydrodynamic simulations.
Nuclear Physics & RIKEN Theory Seminar
"Initial conditions in high energy nucleusnucleus collisions"
Presented by Yacine MetharTani, Orsay
Friday, November 30, 2007, 2 pm
Small Seminar Room, Bldg. 510
We provide a solution for the classical gauge field produced in a high energy nucleusnucleus collision in light cone gauge where we have neglected final state interactions. Also, we describe a systematic formalism to include them. This could be used to study gluon production in the initial stage of heavy Ion collisions, and estimate the importance of final state interactions.
Nuclear Physics & RIKEN Theory Seminar
"Inhomogeneous Gluon Condensates and Magnetic Fields in Color Superconductivity"
Presented by Efrain Ferrer, Western Illinois University
Tuesday, November 20, 2007, 2 pm
Small Seminar Room, Bldg. 510
In this talk I will discuss two color superconductors on which the generation of an inhomogeneous gluon condensate can remove the instability of the ground state. In the first part, I will consider a system in the presence of an external magnetic field and will show how the gluon condensate is formed at fields larger than a critical value. In the second part, I will discuss a case with no external magnetic field. Here, the inhomogeneous gluon condensation is the result of pairing stress in the framework of the twoflavor color superconductor. We will see that the gluon condensate in turn induces a magnetic field. Finally, I will discuss how the generation of a strong magnetic field in the dense cores of compact stellar objects can be of interest for the physics of magnetars.
Nuclear Physics & RIKEN Theory Seminar
"HighEnergy Hadronic Collisions: Multiple Scatterins, Saturation, Factorization"
Presented by Francois Gelis, CERN
Friday, August 10, 2007, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Agnes Mocsy
In this talk, I will discuss highenergy hadronic collisions involving moderate momentum transfers. Such reactions are the realm of multiple scatterings and gluon saturation, and cannot be handled by the usual pQCD approaches. I will show how to study such collisions in the Color Glass Condensate framework; and explain how, at leading order, the problem reduces to finding classical solutions of the YangMills equations. I'll also discuss ongoing work that aims at studying loop corrections and factorization in this framework.
Nuclear Physics & RIKEN Theory Seminar
"SISCone: A Practical Seedless Infrared Safe Cone Jet Algorithm"
Presented by Gregory Soyez
Tuesday, June 12, 2007, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Tuomas Lappi
Jet algorithms are used everywhere in today's experiments and related theoretical computations. I will start by shortly introducing the different clustering algorithms usually used, in particular, the "cone algorithm". Then, I will show that none of the existing cone algorithms satisfy the basic requirements for practical usage. I will show how that longstanding issue can be solved by introducing a new algorithm: SISCone, and investigate its physical consequences. In the last part of the talk, I will introduce the notion of "jet area" and discuss its practical applications.
Nuclear Physics & RIKEN Theory Seminar
"Elliptic Flow of Thermal Photons and Dileptons"
Presented by Rupa Chatterjee, Ohio State University
Friday, June 8, 2007, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Agnes Mocsy
Elliptic flow of thermal photons and dileptons for 200A GeV Au+Au collisions at RHIC exhibits a rich structure as a function of transverse momentum and invariant mass using hydrodynamic model. Thermal photons and dileptons are emitted from every stage of the expanding system and their transverse momentum spectra and elliptic flow provide differential windows into various stages of the fireball expansion. Contrary to hadron elliptic flow, which increases monotonically with p_T, elliptic flow of thermal photons is predicted to first rise and then fall again. In case of thermal dilepton elliptic flow, the invariant mass of the lepton pair provides an additional continuously tunable parameter for such study.
Nuclear Physics & RIKEN Theory Seminar
"Magnetic quasiparticle component in high temperature QCD"
Presented by Chris KorthalsAltes, Centre de Physique theorique
Friday, April 27, 2007, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Harmen Warringa
Traditionally the hot QCD plasma is thought of as a quarkgluon soup. However the soup is a lot spicier: lattice simulations in quarkless gluodynamics show there must be a colour magnetic component. A hoist of data is within 1 to 2 % consistent with an octet of coloured monopoles. They are dilute, the diluteness given by the empirically small ratio of string tension to the mass gap. They are subject to a chemical potential, and can Bosecondense below some critical temperature.
Nuclear Physics & RIKEN Theory Seminar
"Physical Predictions with Mixed Action Lattice QCD"
Presented by Andre WalkerLoud, University of Maryland
Friday, March 30, 2007, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Agnes Mocsy
There has recently been a rapid growth in the use of mixed action or hybrid lattice QCD simulations for the computation of hadronic matrix elements. Mixed action simulations allow one to construct hadronic source and sink operators with chirally symmetric discretization methods for the valence fermions (which are numerically expensive) in the background of gauge configurations which are generated with (numerically cheaper) discretization methods for the sea fermions that violate chiral symmetry. Using effective field theory methods, I will show that the chiral symmetry of the valence fermions is strong enough to suppress sources of chiral symmetry breaking associated with the lattice spacing artifacts which generally plague lattice simulations. This leads to a nearly universal form for the extrapolation formulae of hadronic observables, independent of the discretization method used for the sea fermions. For quantities protected by chiral symmetry, the counterterm structure is identical to the physical counterterm structure, which arises in chiral perturbation theory. These realizations are only apparent when one uses an onshell renormalization scheme, which I will explicitly demonstrate. I will also discuss the general implications this has for extrapolation formulae both on and off the lattice. I will then make use of these observations to discuss several hadronic observables with an emphasis on twohadron systems. Finally I will use this understanding and existing lattice results to make predictions of quantities not directly measured in lattice simulations. In particular, I make an explicit prediction for the I=1 KK scattering length.
Nuclear Physics & RIKEN Theory Seminar
"Onset of J/psi Melting in QuarkGluon Fluid at RHIC"
Presented by Taku Gunji, University of Tokyo
Monday, March 19, 2007, 2 pm
Bldg. 510, Room 3192
Hosted by: Agnes Mocsy
A strong J/psi suppression in central Au+Au collisions has been observed by the PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC). We develop a hydro+J/psi model in which hot quarkgluon matter is described by the full (3+1)dimensional relativistic hydrodynamics and J/psi is treated as an impurity traversing through the matter. The experimental J/psi suppression pattern in midrapidity is reproduced well by the sequential melting of chi_c, psi',and J/psi in dynamically expanding fluid. The melting temperature of directly produced J/psi is well constrained by the participantnumber dependence of the J/psi suppression and is found to be about 2.1T_{c} with T_{c} being the pseudocritical temperature.
Nuclear Physics & RIKEN Theory Seminar
"Dimuon transverse momentum spectra as a tool to characterize the emission region in heavyion collisions"
Presented by Thorsten Renk, University of Jyvaskyla, Finland
Friday, March 2, 2007, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Agnes Mocsy
Previous dilepton measurements in heavyion collisions have mainly focused on invariant mass spectra to clarify inmedium changes of vector meson properties. However, a dimuon is characterized by two scales  invariant mass M and transverse momentum p_T. Like transverse momentum spectra of hadrons, p_T spectra of dileptons arise from an interplay between emission temperature and collective transverse flow, whereas the invariant mass is insensitive to flow. Having two control parameters of which only one is sensitive to flow allows at given M to characterize the emission region in terms of average temperature and flow. Thus, one is able to study what phases of the fireball evolution radiate into a given mass window. I demonstrate this technique using the dimuon transverse momentum spectra measured in InIn collisions by the NA60 collaboration and present strong arguments that a thermalized evolution phase with T 170 MeV leaves an imprint in the spectra.
Nuclear Physics & RIKEN Theory Seminar
"Phases of QCD: lattice thermodynamics, quasiparticles and Polyakov loop"
Presented by Claudia Ratti, ECT  Trento
Friday, January 19, 2007, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Agnes Mocsy
QCD thermodynamics is investigated by means of the Polyakovloopextended Nambu JonaLasinio (PNJL) model, in which quarks couple simultaneously to the chiral condensate and to a background temporal gauge field representing Polyakov loop dynamics. The behaviour of the Polyakov loop as a function of temperature is obtained by minimizing the thermodynamic potential of the system. A Taylor series expansion of the pressure is performed. Pressure difference and quark number density are then evaluated up to sixth order in quark chemical potential, and compared to the corresponding lattice data. The validity of the Taylor expansion is discussed within our model, through a comparison between the full results and the truncated ones.
Nuclear Physics & RIKEN Theory Seminar
"Equation of State of Gluon Plasma from Local Action"
Presented by Daniel Zwanziger, New York University
Friday, November 3, 2006, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Tuomas Lappi
We consider a local, renormalizable, BRSTinvariant action for QCD in Coulomb gauge that contains auxiliary bose and fermi ghost fields. It possess a nonperturbative vacuum that spontaneously breaks BRSTinvariance. The vacuum condition leads to a gap equation that introduces a mass scale. Calculations are done to oneloop order in a perturbative expansion about this vacuum. They are free of the finite$T$ infrared divergences found by Lind\'{e} and which occur in the order $g^6$ corrections to the StefanBoltzmann equation of state. We obtain a finite result for these corrections. We calculate the ghost propagator and colorCoulomb potential to oneloop and find that they are long range, whereas the 3dimensionally transverse wouldbe physical gluon propagator is suppressed like ${\bf k}^2$ at small ${\bf k}$. These oneloop results accord with the Gribov scenario in Coulomb gauge and with recent numerical determinations of these quantities. When the auxiliary fields are integrated out, one obtains the standard Coulomb gauge action with a cutoff at the Gribov horizon.
RIKEN Lunch Seminar
"Quality Between Experiment and Theory in FewBody Final States"
Presented by Pia Thorngren, Uppsala University
Thursday, November 2, 2006, 12:30 pm
2160, Bldg. 510A
Hosted by: Gerry Bunce
An analysis technique that treats experimental data and theoretical calculations on an equal footing by applying identical selection criteria has been developed. The so called sampling method integrates predictions from a theoretical model for true comparison with experiment. The novel approach takes into account acceptance as well as nonuniformities of the detection efficiencies and is suitable for any kinematically complete experiment with three (or more) particles in the final state. The straightforward procedure will be illustrated with the employment of the sampling method to the analysis of polarization observables in a dp breakup reaction. The data were taken using a vector and tensor polarized deuteron beam in conjunction with a polarized hydrogen target. The theoretical calculations were carried out in the Faddeev framework.
Nuclear Physics & RIKEN Theory Seminar
"Bulk Viscosity in 2SC Quark Matter"
Presented by Andreas Schmitt, Washington University
Friday, October 20, 2006, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Raju Venugopalan
Quark matter inside a compact star is most likely a color superconductor Many suggestions have been made for possible colorsuperconducting phases, from more or less conventional BCS superconductors to more exotic ones, breaking rotational or translational invariance and exhibiting gapless modes One approach to determine the ground state among this multitude of possibilities is to compute their transport properties and compare the resulting predictions with astrophysical observations I will discuss one of these transport properties, namely bulk viscosity of threeflavor colorsuperconducting quark matter in the 2SC phase Bulk viscosity is necessary to damp "rmodes" in a compact star which otherwise (=assuming a perfect fluid) would grow unstable and lead to rotational frequencies of the star which are incompatible with observations.
Nuclear Physics & RIKEN Theory Seminar
"Cosmological black hole formation and the QCD phase transition"
Presented by Joe Kapusta, University of Minnesota
Friday, October 20, 2006, 11 am
Small Seminar Room, Bldg. 510
Hosted by: D. Kharzeev/T. Lappi
It was first suggested by Jedamzik a decade ago that solar mass black holes could have been formed during a first order QCD phase transition in the early universe. The reason is that during a first order phase transition the speed of long wavelength sound waves is zero, implying a softened equation of state that would allow overdense regions of space to more easily collapse to a black hole. We have studied the critical overdensity necessary to achieve collapse for a variety of QCD equations of state, including parametrizations of a first order phase transition, a second order phase transition, and a rapid crossover. Limits on the abundance of primordial black holes from Jupiter mass to solar mass can provide information on the QCD equation of state.
Nuclear Physics & RIKEN Theory Seminar
"Where Does the Proton's Spin come From?"
Presented by Steven Bass, University of Innsbruck, Austria
Friday, June 2, 2006, 1:30 pm
Small Seminar Room, Bldg. 510
Hosted by: Anna Stasto
We discuss the present status of the proton spin problem and its interface with chiral and axial U(1) dynamics. Present data suggest that gluon and strange sea polarization may be small. The possibility of a subtraction constant in the dispersion relation for the proton's g_1 spin structure function will be discussed. A subtraction at infinity, if finite, is nonperturbative and acts like a like a spinpolarized condensate inside a nucleon: it affects the first moment (and not the higher moments) of polarized parton distributions. We also discuss the Regge to perturbative QCD interface for polarized partons.
Joint Accelerator and Nuclear Physics Seminar
"Establishment of RIKEN Nishina Center for AcceleratorBased Science and Progress of RI Beam Factory Project"
Presented by Yasushige Yano, Director of NishinaAccelerator Research Center, RIKEN, Japan
Friday, May 26, 2006, 11 am
Small Seminar Room, Bldg. 510
Hosted by: Gerry Bunce
Nuclear Physics & RIKEN Theory Seminar
"Studying Core Collapse Supernovae with Neutrinos"
Presented by Cecilia Lunardini, University of Washington
Tuesday, May 16, 2006, 11 am
Building 510, Room 2160
Hosted by: Anna Stasto
Neutrinos are extremely important in a core collapse supernova, as they dominate its energy budget and are involved in a variety of crucial processes in the star. They also give unique information on the interior of the star, opaque to photons, and on the neutrino properties, in particular on the neutrino mixing matrix and mass spectrum. After the observation of neutrinos from SN1987A, the study of supernova neutrinos is entering a new phase, with the first strong bounds on the diffuse flux of neutrinos from all supernovae. These bounds approach the range of theoretical predictions of the flux, so that the time is mature for indepth work to update those predictions and determine their uncertainties. These are dominated by the poor knowledge of the spectra of the neutrinos produced inside a supernova, and have a strong impact on the possibility to use neutrino data to learn on the cosmic supernova rate.
Nuclear Physics & RIKEN Theory Seminar
"Entanglement Entropy, Rindler Space and Impurity Models"
Presented by Gregory Levine, Hofstra University
Friday, April 28, 2006, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Anna Stasto
Even noninteracting quantum fields have entanglements that extend over an infinite range. It follows that the degrees of freedom that lie exclusively within any finite volume region L^d will appear to be in a mixed state and exhibit nonvanishing entropy. Entanglement entropy formed in this fashion was first introduced in the context of black hole quantum mechanics and HawkingBekenstein entropy, where it was found that entanglement entropy is not an extensive quantity but, rather, scales as the area of the bounding surface, S ~ L^(d1). I will discuss entanglement entropy in terms of horizons, Rindler spacetime and the closely related Unruh effect, and then show how these constructions may be used to compute entanglement entropy in a boundary impurity model.
Nuclear Physics & RIKEN Theory Seminar
"Color Superconductivity in a Magnetic Field"
Presented by Vivian Incera, Western Illinois University
Friday, April 21, 2006, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Anna Stasto
This talk will focus on the effects of an external magnetic field in a color superconductor. In threeflavors color superconductivity the electromagnetic field mixes up with one gluon to give rise to a longrange, "in medium" or "rotated" electromagnetic field. Because of this, an externally applied magnetic field penetrates the color superconductor as a "rotated" magnetic field. At weak magnetic fields, the preferred phase for three massless flavors is the ColorFlavorLocking (CFL) phase. However, for strong magnetic fields the structure and magnitude of the gap is changed producing the socalled Magnetic CFL, which is characterized by different lowenergy physics. Details of the MCFL phase will be presented. Some recent results on the effects of a "rotated" magnetic field on the gluon dynamics and the subsequent ground state restructuring will be briefly discussed at the end of the talk.
Nuclear Physics & RIKEN Theory Seminar
"The Pomeron and Gauge/String Duality"
Presented by ChungI Tan, Brown University
Friday, April 14, 2006, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Dima Kharzeev
The traditional description of highenergy smallangle scattering in QCD has two components  a soft Pomeron Regge pole for the tensor glueball, and a hard BFKL Pomeron in leading order at weak coupling. On the basis of gauge/string duality, we present a coherent treatment of the Pomeron. In large$N$ QCDlike theories, we use curvedspace stringtheory to describe simultaneously both the BFKL regime and the classic Regge regime. The problem reduces to finding the spectrum of a single $j$plane Schr\"odinger operator. For ultravioletconformal theories, the spectrum exhibits a set of Regge trajectories at positive $t$, and a leading $j$plane cut for negative $t$, the crossover point being modeldependent. For theories with logarithmicallyrunning couplings, one instead finds a discrete spectrum of poles at all $t$, where the Regge trajectories at positive $t$ continuously become a set of slowlyvarying and closelyspaced poles at negative $t$. Our results agree with expectations for the BFKL Pomeron at negative $t$, and with the expected glueball spectrum at positive $t$, but provide a framework in which they are unified. Effects beyond the single Pomeron exchange are briefly discussed.
Nuclear Physics & RIKEN Theory Seminar
"Inmedium properties of Dmesons at FAIR"
Presented by Laura Tolos, GSI Darmstadt
Friday, April 7, 2006, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Anna Stasto
We have calculated for the first time the Dmeson spectral density at finite temperature within a selfconsistent coupledchannel approach, and discuss implications for inmedium effects of produced Dmesons in heavyion collisions. Treating the DN interaction within a selfconsistent coupledchannel calculation generates dynamically the $\Lambda_c$ (2593) resonance. This resonance is the charm counterpart of the $\Lambda$ (1405) resonance generated from the s wave KN interaction. We find that the quasiparticle peak of the Dmeson in the medium stays close to the free one, indicating a small change in the effective mass for finite density and temperature. Our result is in stark contrast to the large changes claimed in previous model calculations based on QCD sumrules, QMC models or chiral effective lagrangians within the meanfield approximation. Furthermore, the spectral density develops a considerable width due to the coupledchannel structure. The reduced attraction felt by the D meson in hot and dense matter together with the large width observed have important consequences for the Dmeson production in heavyion collisions, in particular for the future CBM and PANDA experiments at FAIR.
Nuclear Physics & RIKEN Theory Seminar
"Spectrum of the Dirac Operator in the Schwinger Model"
Presented by Leonid Shifrin, SUNY  Stony Brook
Friday, March 31, 2006, 2 pm
Small Seminar Room, Bldg. 510
Hosted by: Anna Stasto
Spontaneous chiral symmetry breaking plays an important role in the lowenergy dynamics of QCD. The nonzero chiral condensate is related to the nonzero density of small Dirac eigenvalues through the BanksCasher relation. Further, the lowenergy Dirac spectrum has to satisfy a family of consistency relations called LeutwylerSmilga (LS) spectral sum rules. These sum rules are universal, and the original LS derivation was based on quite general arguments. I will discuss these sum rules in the closely related to (1flavor) QCD but much simpler 2dimensional Schwinger model. The dynamics of the two theories share chiral anomaly, topologically nontrivial vacuum, instantons, dynamical mass generation and confinement. While LS sum rules are the same for both theories, in the Schwinger model it is possible to achieve more detailed microscopic understanding of them. Three different ways to derive LS sum rules in the Schwinger Model will be discussed. The first is based on the clustering property of fermionic correlators and is also valid for 1flavor QCD. The second is an exact microscopic (field theory) derivation. The third relies on 2D bosonization. The clustering property for multiflavor QCD, relations with Random Matrix Theory and relevance to lattice studies will be also briefly discussed.