Thermalization in a Hartree ensemble approximation to quantum field dynamics - art. no. 025016

For homogeneous initial conditions, Hartree (Gaussian) dynamical approximat ions are known to have problems with thermalization because of insufficient scattering. We attempt to improve on this by writing an arbitrary density matrix as a superposition of Gaussian pure states and applying the Hartree approximation to each member of such an ensemble. Particles can then scatte r via their back reaction on the typically inhomogeneous mean fields. Start ing from initial states that are far from equilibrium we numerically comput e the time evolution of particle distribution functions and observe that th ey indeed display approximate thermalization on intermediate time scales by approaching a Bose-Einstein form. However, for very large times the distri butions drift towards classical-like equipartition.