Bjorken Flow, Plasma Instabilities, and Thermalization

TL;DR

This paper analyzes the process of thermalization in high-energy heavy ion collisions using weak-coupling QCD, emphasizing the role of plasma instabilities and the timeline toward a thermal Quark-Gluon Plasma.

Contribution

It provides a comprehensive parametric weak-coupling analysis of thermalization, highlighting plasma instabilities as the dominant mechanism from immediately after collision to near equilibrium.

Findings

Plasma instabilities drive the system toward isotropy initially.

The system becomes more anisotropic due to expansion and diluteness.

Thermalization completes around 2/5  Q^{-1} with a nearly thermal Quark-Gluon Plasma.

Abstract

At asymptotically high energies, thermalization in heavy ion collisions can be described via weak-coupling QCD. We present a complete treatment of how thermalization proceeds, at the parametric weak-coupling level. We show that plasma instabilities dominate the dynamics, from immediately after the collision until well after the plasma becomes nearly in equilibrium. Initially they drive the system close to isotropy, but Bjorken expansion and increasing diluteness makes the system again become more anisotropic. At time \tau ~ \alpha^(-12/5) Q^(-1) the dynamics become dominated by a nearly-thermal bath; and at time \tau ~ \alpha^(-5/2) Q^(-1)$ the bath comes to dominate the energy density, completing thermalization. After this time there is a nearly isotropic and thermal Quark-Gluon Plasma.