Second-order Hydrodynamics in Next-to-Leading-Order QCD

Abstract

We compute the hydrodynamic relaxation times ${\tau }_{\pi }$ and ${\tau }_j$ for hot QCD at next-to-leading order in the coupling with kinetic theory. We show that certain dimensionless ratios of second-order to first-order transport coefficients obey bounds which apply whenever a kinetic theory description is possible; the computed values lie somewhat above these bounds. Strongly coupled theories with holographic duals strongly violate these bounds, highlighting their distance from a quasiparticle description.

Comments: 5 pages, 3 figures. v2: note and reference added, version accepted for publication on Phys. Rev. Lett