Linearized nonequilibrium dynamics in nonconformal plasma

TL;DR

This paper studies the behavior of nonhydrodynamic modes in holographic models resembling lattice QCD, revealing how their damping and dynamics change near the crossover transition, with implications for understanding quark-gluon plasma.

Contribution

It provides a detailed analysis of quasinormal mode damping and ultralocality in nonconformal holographic models, highlighting their behavior near the QCD crossover.

Findings

Damping of quasinormal modes decreases by about a factor of two near the transition.

Damping correlates with the speed of sound and is independent of UV details.

Nonhydrodynamic degrees of freedom remain ultralocal even away from conformality.

Abstract

We investigate the behaviour of the lowest nonhydrodynamic modes in a class of holographic models which exhibit an equation of state closely mimicking the one determined from lattice QCD. We calculate the lowest quasinormal mode frequencies for a range of scalar self-interaction potentials and find that the damping of the quasinormal modes at the phase transition/crossover falls off by a factor of around two from conformality after factoring out standard conformal temperature dependence. The damping encoded in the imaginary part of the frequencies turns out to be correlated with the speed of sound and is basically independent of the UV details of the model. We also find that the dynamics of the nonhydrodynamic degrees of freedom remains ultralocal, even to a higher degree, as we deviate from conformality. These results indicate that the role of nonhydrodynamic degrees of freedom in the vicinity of the crossover transition may be enhanced.