One-loop corrections to $\eta/s$ in AdS$_4$/CFT$_3$

TL;DR

This paper investigates quantum one-loop corrections to the shear viscosity to entropy ratio in AdS4/CFT3, finding no correction to shear viscosity but a spin-dependent logarithmic correction to entropy, challenging the universality of the KSS bound.

Contribution

It demonstrates that quantum corrections do not alter shear viscosity at one-loop but introduce a spin-dependent entropy correction, questioning the fundamental nature of the KSS bound.

Findings

Shear viscosity remains uncorrected at one-loop.

Entropy receives a logarithmic correction depending on particle spin.

The KSS bound is not a fundamental property beyond classical physics.

Abstract

We study quantum corrections at one-loop order to the shear viscosity to entropy ratio by implementing the Vilkovisky-Barvinsky effective action in asymptotically Anti-de Sitter spacetimes. The shear viscosity is shown to receive no corrections at this order, but the entropy acquires a logarithmic correction. The coefficient of this logarithm turns out to depend on the spin of the particles running in the loop and it can be either positive or negative. On the basis of this result, we argue that the Kovtun-Son-Starinets bound cannot be seen as a fundamental property of nature beyond the classical regime.