Chemical equilibration in weakly coupled QCD

Abstract

We study thermalization, hydrodynamization, and chemical equilibration in out-of-equilibrium quark-gluon plasma starting from various initial conditions using QCD effective kinetic theory, valid at weak coupling. In non-expanding systems gauge bosons rapidly lose information of the initial state and achieve kinetic equilibrium among themselves, while fermions approach the equilibrium distribution only at a later time. In systems undergoing rapid longitudinal expansion, both gluons and quarks are kept away from equilibrium by the expansion, but the evolution is well described by fluid dynamics even before local thermal equilibrium is reached. For realistic couplings we determine the ordering between the separate hydrodynamization, chemical equilibration and thermalization time scales to be tau(hydro) < tau(chem) < tau(therm).