The shear viscosity of gauge theory plasma with chemical potentials

TL;DR

The paper addresses whether the holographic bound $\frac{\eta}{s}=\frac{1}{4\pi}$ extends to strongly coupled gauge theory plasmas with chemical potentials. It uses gauge/gravity duality, working with type IIB backgrounds and a consistent truncation to a $(D+2)$-dimensional gauged supergravity (the STU model) describing black brane solutions carrying multiple $U(1)$ charges. By perturbing the metric and computing the retarded Green's function $G^R_{12,12}(\omega,0)$ in the low-frequency limit, the authors show $G^R_{12,12}(\omega,0)=-\frac{i\omega s}{4\pi}$, which implies $\eta=\frac{s}{4\pi}$ and thus $\frac{\eta}{s}=\frac{1}{4\pi}$. The result supports a broad universality of holographic hydrodynamics across theories with global charges and chemical potentials, under the stated assumptions about horizon regularity and consistent truncations.

Abstract

We consider strongly coupled gauge theory plasma with conserved global charges that allow for a dual gravitational description. We study the shear viscosity of the gauge theory plasma in the presence of chemical potentials for these charges. Using gauge theory/string theory correspondence we prove that at large 't Hooft coupling the ratio of the shear viscosity to the entropy density is universal.