Notes on the bulk viscosity of holographic gauge theory plasmas

TL;DR

This paper introduces a new analytic method to calculate the bulk viscosity of high-temperature holographic gauge theory plasmas with broken conformal symmetry, verifying a conjectured viscosity bound.

Contribution

It presents a novel technique using Ward identities and black hole backgrounds to derive an explicit expression for bulk viscosity in these theories.

Findings

Analytic expression for bulk viscosity derived

Verification of the viscosity bound at high temperature

Bound saturation when conformal symmetry-breaking operator is marginal

Abstract

A novel technique is used to compute the bulk viscosity of high temperature holographic gauge theory plasmas with softly broken conformal symmetry. Working in a black hole background which corresponds to a non-trivial solution to the Navier-Stokes equation, and using a Ward identity for the trace of the stress-energy tensor, it is possible to obtain an analytic expression for the bulk viscosity. This can be used to verify the high temperature limit of a conjectured bound on the bulk viscosity for these theories. The bound is saturated when the conformal symmetry-breaking operator becomes marginal.