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 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 τ hydro < τ chem < τ therm .

Exact solution for the non-equilibrium attractor in number-conserving relaxation time approximation

“…It would be very interesting to consider the 2 ↔ 2 scalar kinetic theory using Monte-Carlo-based transport in order to compare with the exact results obtained herein using number-conserving RTA. It would also be interesting to make comparisons with the attractor extracted from the effective kinetic theory framework of Kurkela et al, particularly in the case that baryon number conservation is at play [8,12,88,89].…”

Chemical Equilibration in Hadronic Collisions

“…We consider N c = 3 colors and N f = 3 flavours of massless fermions with equal quark-antiquark content, i.e., at vanishing baryon chemical potential µ B = 0. For the explicit expressions of collision kernels and the regularization procedure of the infrared divergences see the published work [7].…”

Prescaling and Far-from-Equilibrium Hydrodynamics in the Quark-Gluon Plasma

“…using the numerical setup developed in Refs. [19,20]. order elastic scatterings in the coupling α s ≡ g 2 /(4π).…”

“…However, our results establish the existence of a new hydrodynamic regime far away from equilibrium at early times, which has not much to say about the later time approach to thermal equilibrium, where more conventional hydrodynamic descriptions should be applied. The subsequent evolution of the quark-gluon plasma towards thermal equilibrium with QCD kinetic theory is the subject of a separate work [19,20].…”