Initial States and Time Evolution in Nonequilibrium Quantum Field Theory

We consider a statistical system, described by a relativistic neutral scalar massive quantum field with t-dependent mass parameter. By assumption, the system is represented at time t0 by a nonequilibrium initial gaussian density operator ρin,g with spatial inhomogeneities (potentially interesting for the cosmological inflaton and, qualitatively, for relativistic plasmas). In order to describe the out-of-equilibrium time evolution for t>t0, as determined by ρin,g, one requires the corresponding nonequilibrium free correlators, as a necessary step before introducing interactions. We report, in outline, the space-time structures of those free nonequilibrium correlators.