Nonequilibrium two-particle irreducible evolution of the O(N) model with longitudinal expansion

Motivated by the problem of thermalization in heavy ion collisions, we present numerical simulations of the nonequilibrium evolution of the O(N) model in 1 + 2 dimensions with longitudinal expansion and in the presence of a background field. We work in the next-to-leading-order approximation of the 1/N expansion and consider both the strong and weak coupling cases. Special emphasis is put on the difference between the two-particle irreducible formalism and the classical statistical approach. In the two-particle irreducible case at strong coupling, we find some evidence of the Bose-Einstein (exponential) distribution in the expanding system.