JUN
21
Tuesday
Physics Colloquium
"Sterile Neutrinos as the Origin of Dark and Baryonic Matter"
Presented by Mikhail Shaposhnikov, EPFL
3:30 pm, Large Seminar Room, Bldg. 510
Tuesday, June 21, 2016, 3:30 pm
Hosted by: 'Robert Pisarski'
I will discuss how three sterile neutrinos alone can simultaneously explain neutrino oscillations, the observed dark matter, and the baryon asymmetry of the Universe without new physics above the Fermi scale. The experimental prospects to search for these particles will be outlined.
JUN
24
Friday
Nuclear/Riken Theory Committee
"On Pressure Isotropization in Heavy-Ion Collisions"
Presented by Bin Wu, The Ohio State University
2 pm, Small Seminar Room, Bldg. 510
Friday, June 24, 2016, 2:00 pm
Hosted by: ''Soeren Schlichting''
In this talk, I would like to start with a brief introduction to non-equilibrium quantum field theory in the Schwinger-Keldysh formalism. This formalism provides a systematic way to study isotropization and other time-dependent non-equilibrium (and equilibrium) phenomena in heavy-ion 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 non-renormalizable. This helps us understand better the applicability of such an approximation. it is now well-known that isotropization can not be established before the breakdown of the CSA. We then use another approximation, the quasi-particle 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 Schwinger-Keldysh formalism. Some preliminary results shall be reported.
JUN
28
Tuesday
Nuclear Physics Seminar
"Two Photon Exchange and the Proton Form Factor Problem"
Presented by Lawrence Weinstein, Old Dominion University
11 am, Small Seminar Room, Bldg. 510
Tuesday, June 28, 2016, 11:00 am
Hosted by: 'Oleg Eyser'
The electromagnetic form factors of the proton as measured by polarized and unpolarized electron scattering experiments differ by up to a factor of three at large momentum transfer. Calculations show that this discrepancy can be reconciled by treating the interaction in 2nd Born Approximation, i.e., including two photon exchange (TPE). While calculation of TPE effects is highly model dependent, these effects can be measured directly by comparing elastic electron-proton and positron-proton scattering. Three experiments, TPE at Jefferson Lab, VEPP-3 at Novosibirsk, and OLYMPUS at DESY, measured this. VEPP-3 and OLYMPUS used alternating monochromatic e+ and e- beams in storage rings; TPE created a tertiary mixed simultaneous e+/e- beam covering a wide range of energies. This talk will present the proton form factor problem, the experimental effort to measure the positron-electron ratio (with special emphasis on the Jefferson Lab experiment), and the results.