Bose--Einstein Condensation and Thermalization of the Quark Gluon Plasma

In ultra-relativistic heavy ion collisions, the matter formed shortly after the collision is a Glasma, a dense non-equilibrium system of gluons characterized by a semi-hard momentum scale $Q_s$. Simple power counting arguments indicate that this system is over-occupied--the gluon occupation number is parametrically large when compared to a system in thermal equilibrium with the same energy density. Because soft elastic scatterings dominate over the inelastic processes on short time scales, this over-occupation of gluon modes leads to the rapid formation of a Bose--Einstein condensate containing a large fraction of gluons. We argue that the Glasma, albeit weakly coupled, is strongly self interacting but may have a fixed anisotropy due a difference in average longitudinal and transverse momentum. The Glasma will generate flow and jet quenching, and will contain a Bose--Einstein condensate until parametrically late times when inelastic interactions become important, initiating the rapid decay of the condensate. These late times also correspond to the time scale necessary to thermalize the system.