The process of equilibration in ${\phi }^4$ theory is investigated for a homogeneous system in $3+1$ dimensions and a variety of out-of-equilibrium initial conditions, both in the symmetric and broken phase, by means of the 2PI effective action. Two $\Phi$-derivable approximations including scattering effects are used: the two-loop and the basketball, the latter corresponding to the truncation of the 2PI effective action at $\mathcal{O}({\lambda }^2)$. The approach to equilibrium, as well as the kinetic and chemical equilibration is investigated.

• Received 25 May 2005

DOI:https://doi.org/10.1103/PhysRevD.72.025014