Hydrodynamics from scalar black branes

TL;DR

This paper uses gauge/gravity duality to study hydrodynamics of strongly coupled QFTs with hyperscaling violation, revealing unique diffusion behavior and confirming the universal shear viscosity to entropy ratio in these models.

Contribution

It introduces a new class of scalar black brane solutions with hyperscaling violation and analyzes their hydrodynamic properties, highlighting differences from standard AdS duals.

Findings

$ R $-charge diffusion scales non trivially with temperature.

Shear viscosity to entropy ratio $ \eta/s $ equals $ 1/4\pi $ in both extremal and non-extremal limits.

Quantum critical systems with hyperscaling violation may belong to a distinct universality class.

Abstract

In this paper, using the Gauge/gravity duality techniques, we explore the hydrodynamic regime of a very special class of strongly coupled QFTs that come up with an emerging UV length scale in the presence of a negative hyperscaling violating exponent. The dual gravitational counterpart for these QFTs consists of scalar dressed black brane solutions of exactly integrable Einstein-scalar gravity model with Domain Wall (DW) asymptotics. In the first part of our analysis we compute the $ R $-charge diffusion for the boundary theory and find that (unlike the case for the pure $ AdS_{4} $ black branes) it scales quite non trivially with the temperature. In the second part of our analysis, we compute the $ \eta/s $ ratio both in the non extremal as well as in the extremal limit of these special class of gauge theories and it turns out to be eqaul to $ 1/4\pi $ in both the cases. These results therefore suggest that the quantum critical systems in the presence of (negative) hyperscaling violation at UV, might fall under a separate universality class as compared to those conventional quantum critical systems with the usual $ AdS_4 $ duals.