Heavy quark diffusion coefficient during hydrodynamization -- non-equilibrium vs. equilibrium

TL;DR

This paper calculates the heavy quark diffusion coefficient during the early stages of quark-gluon plasma formation, comparing non-equilibrium and equilibrium states, revealing deviations within 30% and directional dominance depending on system occupation.

Contribution

It provides the first detailed comparison of heavy quark diffusion in non-equilibrium and near-equilibrium conditions during hydrodynamization using effective kinetic theory.

Findings

Deviations between nonthermal and thermal diffusion coefficients are within 30%.

Transverse diffusion dominates at high occupation numbers, while longitudinal dominates in underoccupied systems.

The jet quenching parameter evolves smoothly from glasma to hydrodynamical regimes.

Abstract

We compute the heavy quark momentum diffusion coefficient using effective kinetic theory for a system going through bottom-up isotropization until approximate hydrodynamization. We find that when comparing the nonthermal diffusion coefficient to the thermal one for the same energy density, the observed deviations throughout the whole evolution are within 30% from the thermal value. For thermal systems matched to other quantities we observe considerably larger deviations. We also observe that the diffusion coefficient in the transverse direction dominates at large occupation number, whereas for an underoccupied system the longitudinal diffusion coefficient dominates. Similarly, we study the jet quenching parameter, where we obtain a smooth evolution connecting the large values of the glasma phase with the smaller values in the hydrodynamical regime.