Universality of the shear viscosity in supergravity

TL;DR

This paper demonstrates that gauge theories with holographic supergravity duals always reach the proposed shear viscosity bound, indicating a universal behavior in strongly coupled fluids.

Contribution

It shows that the shear viscosity bound is universally saturated in gauge theories with holographic supergravity duals at large 't Hooft coupling.

Findings

Shear viscosity bound is always saturated in these theories.

The result supports the universality of the viscosity bound.

Holographic duality provides a proof of the bound's saturation.

Abstract

Kovtun, Son and Starinets proposed a bound on the shear viscosity of any fluid in terms of its entropy density. We argue that this bound is always saturated for gauge theories at large 't Hooft coupling, which admit holographically dual supergravity description.