From preheating to thermal equilibrium nonlinear dynamics of interacting fields

This paper presents the first fully nonlinear study of the development of equilibrium after preheating. Preheating is the exponentially rapid transfer of energy from the nearly homogeneous inflation field to fluctuations of the inflation itself and/or other fields. This rapid transfer leaves these fields in a highly nonthermal state with energy concentrated in infrared modes. We have performed lattice simulations of the evolution of these fields during and after preheating for a variety of inflationary models. We describe a number of generic features that govern the thermalization process in all of these models. Notably, we see that once a single field is amplified through parametric resonance or other mechanisms it rapidly excites other fields to exponentially large occupation numbers. All of these fields quickly acquire nearly thermal spectra in the infrared and then begin to gradually scatter their energy into higher momentum modes, thus bringing the spectra into thermal equilibrium.