Nonequilibrium quark production in the expanding QCD plasma

TL;DR

This study uses real-time lattice simulations to investigate how quarks are produced in an expanding QCD plasma, revealing a linear growth in quark number consistent with kinetic theory predictions involving two-to-two scatterings.

Contribution

It demonstrates that quark production in an expanding QCD plasma can be accurately described by kinetic theory with simple scattering processes, extending previous gluonic dynamics findings.

Findings

Quark number grows linearly after initial rapid increase

Growth rate matches kinetic theory estimates

Supports the role of two-to-two scatterings in early thermalization

Abstract

We perform real-time lattice simulations of nonequilibrium quark production in the longitudinally expanding QCD plasma. Starting from a highly occupied gluonic state with vacuum quark sector, we extract the time evolution of quark and gluon number densities per unit transverse area and rapidity. The total quark number shows after an initial rapid increase an almost linear growth with time. Remarkably, this growth rate appears to be consistent with a simple kinetic theory estimate involving only two-to-two scattering processes in small-angle approximation. This extends previous findings about the role of two-to-two scatterings for purely gluonic dynamics in accordance with the early stages of the bottom-up thermalization scenario.