New developments in thermal field theory

8 Oct 2018, 08:00 → 12 Oct 2018, 19:00 Europe/Zurich

4/2-037 - TH meeting room (CERN)

The activities of the Institute are open to everyone. However the TH group can only invite, host and provide logistic support (i.e. office space, registration and access to CERN, advanced Hostel booking, etc) to a limited number of official participants. To apply for registration as official attendee, fill the application form.

Monday 8 October

10:00 → 11:00 Collisions in AdS and the Quantum Null Energy Condition

In this talk I will give an introduction to the Quantum Null Energy Condition (QNEC), which is a unique local energy condition conjectured to be valid for any QFT. QNEC relates the normal null energy condition (NEC) with the second null derivative of the entanglement entropy and was inspired from the second law of black hole thermodynamics, even though it is valid in QFTs without gravity. After this introduction I will present some sample computations in holography, where entanglement entropy can be computed using the dual geometry. This example in particular includes regions in shock wave collisions, that were known to violate NEC, but now found to saturate QNEC. I end with upcoming work on QNEC in 1+1D holographic CFTs, including leading order quantum corrections in the bulk.

Speaker: Wilke van der Schee (MIT)

Tuesday 9 October

10:00 → 11:00 The QCD critical point hunt: characterizing and quantifying the dynamics of critical fluctuations

Experimentally locating the QCD critical point is one of the important scientific goal for the relativistic heavy-ion collision program, with potential connections to a plethora of deep questions on the phase diagram of nuclear matter. I will discuss the qualitative features of offequilibrium effects for the fireballs passing close to the critical point based on Kibble-Zurek dynamics. I will then present a novel theoretical framework on the quantitative description of hydrodynamic fluctuations near the critical point, namely “hydro+”. I will show the first results on the numerical simulations of “hydro+”, and discuss the interesting connection of “hydro+” to other approaches of fluctuating hydrodynamics.

Speaker: Dr Yi Yin (MIT)

Wednesday 10 October

10:00 → 11:00 The problem of overlapping formation times: Calculating overlap corrections in QCD and QED

High energy particles passing through medium primarily lose energy by showering through bremsstrahlung and pair production. At high energies, the quantum mechanical duration of the splitting process, called the formation time exceeds the mean free time between collisions with the medium and leads to a significant suppression of the splitting rate. This suppression is known as the Landau-Pomeranchuk-Migdal (LPM) effect. A long standing problem in field theory had been to calculate this effect for situations where the formation times of two consecutive splittings overlap. We (Peter Arnold, myself and Han Chih-Chang) developed and implemented field theory formalism to calculate such overlap corrections to real double splittings and overlapping virtual processes in large-Nc QCD and large-Nf QED. Here Nc is the number of colors and Nf is the number of electron flavors. In this talk, I will explain our formalism for calculating these corrections going beyond soft emissions as well as giving a preview of our results for overlap corrections to in-medium electron energy loss and stopping distances.

Speaker: Dr Shahin Iqbal (National Centre for Physics)

Thursday 11 October

10:00 → 11:00 Shear Viscosity of Hot Hadron Gas Estimated From Data

The specific shear viscosity eta/s of quark gluon plasma has been extracted with increasing accuracy from comparing viscous fluid dynamics calculations to data. Together with lattice QCD and new NLO perturbative calculations a consistent picture seems to emerge. On the other hand, for hot hadron gas below Tc uncertainties are larger, with transport models typically predicting very large eta/s up to Tc. We explore the possibility to constrain eta/s of hot hadron gas from data by utilizing the deformation of particle distributions in the presence of shear stress. Following this strategy we obtain values of the specific shear viscosity vs temperature. Results are consistent between LHC and RHIC data, and values of eta/s drop significantly between 110 and 140 MeV temperature. We make an effort to estimate the systematic uncertainties on the numbers we extract.

Speaker: Rainer Fries (Texas A&M University)

Friday 12 October

10:00 → 11:00 NNNLO pressure of cold quark matter: leading logarithm

At high baryon chemical potential mu, the pressure of QCD allows a weak-coupling expansion in the QCD coupling parameter alpha_s. The result is currently known up to and including the full NNLO alpha_s^2, first computed in 1977 for massless quarks by Freedman and McLerran. Starting at this order, computations are complicated by the modification of particle propagation in a dense medium, which necessitates non-perturbative treatment of the so-called soft scale alpha_s^(1/2) mu. In this talk, I will describe a Hard-Thermal-Loop scheme for capturing the contributions of this scale to the weak-coupling expansion, and show how to use it to determine the leading-logarithm contribution at NNNLO: alpha_s^3 ln(alpha_s)^2. This result is the first improvement to the pressure of massless cold quark matter in 40 years. I will also say a few words about current work being undertaken to expand this result to the subleading linear logarithm: alpha_s^3 ln(alpha_s).

Speaker: Tyler Gorda (University of Helsinki)