Bulk viscosity of strongly coupled plasmas with holographic duals

TL;DR

This paper introduces a simplified holographic method to compute the bulk viscosity of strongly coupled plasmas, revealing a slight violation of a previously conjectured viscosity bound.

Contribution

The authors present a new approach that requires only the low-frequency Green's function to determine bulk viscosity in holographic models, simplifying prior methods.

Findings

Method reduces computational complexity for bulk viscosity

Observed a slight violation of the viscosity bound

Applicable to QCD-like equations of state

Abstract

We explain a method for computing the bulk viscosity of strongly coupled thermal plasmas dual to supergravity backgrounds supported by one scalar field. Whereas earlier investigations required the computation of the leading dissipative term in the dispersion relation for sound waves, our method requires only the leading frequency dependence of an appropriate Green's function in the low-frequency limit. With a scalar potential chosen to mimic the equation of state of QCD, we observe a slight violation of the lower bound on the ratio of the bulk and shear viscosities conjectured in arXiv:0708.3459.