Hydrodynamics of the cascading plasma

TL;DR

This paper investigates the hydrodynamic properties of the cascading gauge theory plasma using holography, focusing on the speed of sound and bulk viscosity, and explores stability and phase transition characteristics at high temperatures.

Contribution

It provides a detailed calculation of the bulk viscosity and speed of sound in the cascading plasma to order 1/ln(T/Lambda)^4, confirming the bulk viscosity bound and analyzing phase stability.

Findings

Bulk viscosity satisfies the conjectured bound.

Deconfined phase becomes unstable at T_u=0.8749 T_c.

Specific heat diverges near the instability point.

Abstract

The cascading gauge theory of Klebanov et.al realizes a soluble example of gauge/string correspondence in a non-conformal setting. Such a gauge theory has a strong coupling scale Lambda, below which it confines with a chiral symmetry breaking. A holographic description of a strongly coupled cascading gauge theory plasma is represented by a black brane solution of type IIB supergravity on a conifold with fluxes. A characteristic parameter controlling the high temperature expansion of such plasma is 1/ln(T/Lambda). In this paper we study the speed of sound and the bulk viscosity of the cascading gauge theory plasma to order 1/ln(T/Lambda)^4. We find that the bulk viscosity satisfies the bound conjectured in arXiv:0708.3459. We comment on difficulties of computing the transport coefficients to all orders in T/Lambda. Previously, it was shown that a cascading gauge theory plasma undergoes a first-order deconfinement transition with unbroken chiral symmetry at T_c=0.6141111(3) Lambda. We show here that a deconfined chirally symmetric phase becomes perturbatively unstable at T_u=0.8749(0) T_c. Near the unstable point the specific heat diverges as c_V ~ |1-T_u/T|^(-1/2).