On Bulk Viscosity at Weak and Strong 't Hooft Couplings

TL;DR

This paper investigates bulk viscosity in thermal QCD at high temperatures using both weak coupling kinetic theory and strong coupling holography, providing explicit results across different coupling regimes.

Contribution

It compares bulk viscosity at weak and strong 't Hooft couplings in thermal QCD, employing kinetic theory and holographic methods respectively, to derive explicit properties.

Findings

Bulk viscosity is non-zero only in non-conformal theories.

Explicit formulas for bulk viscosity at weak and strong couplings.

Comparison of transport properties across coupling regimes.

Abstract

Bulk viscosity is an important transport coefficient that exists in the hydrodynamical limit only when the underlying theory is non-conformal. One example being thermal QCD with large number of colors. We study bulk viscosity in such a theory at low energies and at weak and strong 't Hooft couplings when the temperature is above the deconfinement temperature. The weak coupling analysis is based on Boltzmann equation from kinetic theory whereas the strong coupling analysis uses non-conformal holographic techniques from string and M-theories. Using these, many properties associated with bulk viscosity may be explicitly derived. This is a shortened companion paper that summarizes some of the results of our longer paper arXiv:1807.04713.