Post-inflationary reheating

We study the two field model for reheating based on the scalar inflaton field phi and its interaction with another scalar field chi through a Lagrangian term 1/2g(2)chi(2)phi(2), much investigated for parametric resonance or preheating. Attention is paid particularly to the quantum excitations of the inflaton field and the metric with a smooth transition from quantum to classical stochastic states, and with reheating followed right through from a specific inflation model to a state including a relativistic (Radiation) fluid. The excitations of the metric (but not the inflaton or chi) are treated perturbatively and the validity of this approach is assessed. For this model our work points to the possibility of the cosmic reheating period ending in a two-component state (one being the radiation fluid and the other nonthermalized inflaton relies) and also to zeta (the curvature parameter for observed cosmic microwave background anisotropies) changing significantly during reheating with parametric resonance.