Thermalization of gluons in spatially homogeneous systems

TL;DR

This paper studies how gluons in spatially homogeneous systems reach thermal equilibrium, revealing distinct stages in under- and over-populated scenarios through Boltzmann equation analysis.

Contribution

It provides a comprehensive analysis of gluon thermalization, detailing the different stages and mechanisms involved in both under- and over-populated initial conditions.

Findings

Soft sector undergoes three stages in under-populated systems: overheating, cooling/overcooling, reheating.

Soft sector undergoes two stages in over-populated systems: overheating and cooling.

Cooling driven by momentum broadening from elastic collisions, following a non-thermal scaling solution.

Abstract

We investigate thermalization of gluons in spatially homogeneous systems using the Boltzmann equation in diffusion approximation. A complete picture on thermalization is obtained for both initially under- and over-populated systems. In an initially under-populated system, we find that its soft sector undergoes three stages: overheating, cooling/overcooling and reheating before full thermalization is achieved. In an initially over-populated system, we find that its soft sector only undergoes two stages towards full thermalization: overheating and cooling. The cooling stage is consistently driven by momentum broadening due to multiple elastic collisions, manifest as a non-thermal scaling solution.