Transport properties of cascading gauge theories

TL;DR

This paper investigates the transport properties of strongly coupled cascading gauge theory plasma using gauge/gravity duality, analytically computing the speed of sound and bulk viscosity at high temperature.

Contribution

It provides the first analytical calculation of sound speed and bulk viscosity in cascading gauge theories at high temperature, confirming previous numerical results.

Findings

Speed of sound matches previous equation of state calculations.

Bulk viscosity is non-zero at leading order in deviation from conformality.

Analytical dispersion relation for sound waves in the plasma.

Abstract

Cascading gauge theories of Klebanov et.al. provide a model within a framework of gauge theory/string theory duality for a four dimensional non-conformal gauge theory with a spontaneously generated mass scale. Using the dual supergravity description we study sound wave propagation in strongly coupled cascading gauge theory plasma. We analytically compute the speed of sound and the bulk viscosity of cascading gauge theory plasma at a temperature much larger than the strong coupling scale of the theory. The sound wave dispersion relation is obtained from the hydrodynamic pole in the stress-energy tensor two-point correlation function. The speed of sound extracted from the pole of the correlation function agrees with its value computed in [hep-th/0506002] using the equation of state. We find that the bulk viscosity of the hot cascading gauge theory plasma is non-zero at the leading order in the deviation from conformality.