OCT
13
Tuesday
Physics Colloquium
"Random Matrices in Physics"
Presented by Hans A. Weidenmuller, Max-Planck-Institut fur Kernphysik, Heidelberg, Germany
3:30 pm, Large Seminar Room, Bldg. 510
Tuesday, October 13, 2015, 3:30 pm
Hosted by: Robert Pisarski
What can we say about a physical system when we know next to nothing about it? In classical physics, the principles of thermodynamics and a few system-specific parameters suffice to make predictions. In quantum physics, random matrices have similar predictive power. That approach-referred to as random-matrix theory-has found wide applications in recent years, in quantum physics and beyond. The use of random matrices in quantum chaos, in complex many-body systems, in disordered systems and in quantum chromodynamics will be presented. Furher applications in physics and mathematics will be briefly mentioned.
OCT
23
Friday
Nuclear Theory/RIKEN Seminar
"Thermal photons from a modern hydrodynamical model of heavy ion collisions"
Presented by Jean-Francois Paquet, Stonybrook University
2 pm, Small Seminar Room, Bldg. 510
Friday, October 23, 2015, 2:00 pm
Hosted by: Soeren Schlichting
Early fluid-dynamical 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 event-by-event 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.
OCT
30
Friday
Nuclear Theory/RIKEN Seminar
"Observable consequences of event-by-event fluctuations of HBT radii"
Presented by Christopher J. Plumberg, Ohio State University
2 pm, Small Seminar Room, Bldg. 510
Friday, October 30, 2015, 2:00 pm
Hosted by: Soeren Schlichting
One of the major lessons from the field of heavy-ion physics in the past several years has been the significance of the role played by event-by-event fluctuations in the evolution of a heavy-ion collision. Their important effects on many momentum-space observables (particle yields and spectra, anisotropic flows, etc.) have already been studied systematically, and some of the properties of their event-by-event distributions, and their consequences for the extraction of medium properties such as the specific viscosity of the quark-gluon plasma (QGP), are already known. In this talk it is pointed out that similar event-by-event fluctuations of spatiotemporal observables provide complementary constraints on our understanding of the dynamical evolution of heavy-ion collisions. The relation of Hanbury Brown-Twiss (HBT) radii extracted from ensemble-averaged correlation function measurements to the mean of their event-by-event 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 quark-hadron transition at a level similar (10-20%) to that which was previously observed for elliptic and quadrangular flow of charged hadrons.
NOV
6
Friday
Nuclear Theory/RIKEN Seminar
"Massless QED in three dimensions with even number of flavors"
Presented by Rajamani Narayanan, Florida International University
2 pm, Small Seminar Room, Bldg. 510
Friday, November 6, 2015, 2:00 pm
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.
NOV
13
Friday
Nuclear Theory/RIKEN Seminar
"Linearly resummed hydrodynamics from gravity"
Presented by Yanyan Bu, Ben Gurion University of the Negev
2 pm, Small Seminar Room, Bldg. 510
Friday, November 13, 2015, 2:00 pm
Hosted by: Soeren Schlichting
Using fluid/gravity correspondence, we study all-order resummed hydrodynamics in a weakly curved spacetime. The underlying microscopic theory is a finite temperature \mathcal{N}=4 super-Yang-Mills theory at strong coupling. To linear order in the amplitude of hydrodynamic variables and metric perturbations, the fluid's stress-energy 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 Gauss-Bonnet correction in the dual gravity, which is equivalent to some 1/N corrections in the dual CFT. To leading order in the Gauss-Bonnet coupling, we find that the memory function is still vanishing.
NOV
20
Friday
HET/RIKEN Lunch Seminar
"Collider Phenomenology of the Right Handed Heavy Neutrinos"
Presented by Arindam Das, University of Alabama
12 pm, Building 510 Room-2-160
Friday, November 20, 2015, 12:00 pm
Hosted by: Amarjit Soni
We study the collider signature of pseudo-Dirac heavy neutrinos in the inverse seesaw scenario, where the heavy neutrinos with mass at the electro-weak 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.
NOV
20
Friday
Nuclear Theory/RIKEN Seminar
"Transversity Distribution and Collins Fragmentation Functions with QCD Evolution"
Presented by Alexei Prokudin, Jefferson Lab
2 pm, Small Seminar Room, Bldg. 510
Friday, November 20, 2015, 2:00 pm
Hosted by: Soeren Schlichting
We study the transverse momentum dependent (TMD) evolution of the Collins azimuthal asymmetries in e+eâˆ' annihilations and semi-inclusive hadron production in deep inelastic scattering (SIDIS) processes. All the relevant coefficients are calculated up to the next-to-leading logarithmic (NLL) order accuracy. By applying the TMD evolution at the approximate NLL order in the Collins-Soper-Sterman (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 back-to-back di-hadron 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.
DEC
4
Friday
Nuclear Theory/RIKEN Seminar
"Semi-classics, complex saddles and real path integrals"
Presented by Tin Sulejmanpasic, North Carolina State University
2 pm, Small Seminar Room, Bldg. 510
Friday, December 4, 2015, 2:00 pm
Hosted by: Soeren Schlichting
I will discuss the use of semi-classics and instanton calculus and argue that, contrary to common wisdom, complex solutions of the equations of motion are a necessary ingredient of any semi-classical expansion. In particular, I will show that without the complex solutions semi-classical expansion of supersymmetric theories cannot be reconciled with supersymmetry. This has a natural interpretation in the Picard-Lefschetz theory.