Hydrodynamics of the cascading plasma

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).