Non-hydrodynamic quasinormal modes and equilibration of a baryon dense holographic QGP with a critical point

TL;DR

This paper analyzes non-hydrodynamic quasinormal modes in a holographic QGP model to understand equilibration times and their behavior near the QCD critical point, providing insights into the medium's return to equilibrium.

Contribution

It offers the first computation of non-hydrodynamic QNM's in a realistic Einstein-Maxwell-Dilaton holographic model for QGP, linking them to equilibration times and critical phenomena.

Findings

Equilibration times decrease with increasing baryon chemical potential.

Modes converge at high temperatures but are separated at the critical point.

The model accurately describes lattice QCD results and QGP properties.

Abstract

We compute the homogeneous limit of non-hydrodynamic quasinormal modes (QNM's) of a phenomenologically realistic Einstein-Maxwell-Dilaton (EMD) holographic model for the Quark-Gluon Plasma (QGP) that is able to: i) {\it quantitatively} describe state-of-the-art lattice results for the QCD equation of state and higher order baryon susceptibilities with $2+1$ flavors and physical quark masses up to highest values of the baryon chemical potential currently reached in lattice simulations; ii) describe the nearly perfect fluidity of the strongly coupled QGP produced in ultrarelativistic heavy ion collisions; iii) give a very good description of the bulk viscosity extracted via some recent Bayesian analyzes of hydrodynamical descriptions of heavy ion experimental data. This EMD model has been recently used to predict the location of the QCD critical point in the QCD phase diagram, which was found to be within the reach of upcoming low energy heavy ion collisions. The lowest quasinormal modes of the $SO(3)$ rotationally invariant quintuplet, triplet, and singlet channels evaluated in the present work provide upper bounds for characteristic equilibration times describing how fast the dense medium returns to thermal equilibrium after being subjected to small disturbances. We find that the equilibration times in the different channels come closer to each other at high temperatures, although being well separated at the critical point. Moreover, in most cases, these equilibration times decrease with increasing baryon chemical potential while keeping temperature fixed.