CLASSICAL DECAY OF THE INFLATON

We present the first fully nonlinear calculation of inflaton decay. We map inflaton decay onto an equivalent classical problem and solve the latter numerically. in the lambda phi(4) model, we find that parametr ic resonance develops slower and ends at smaller values of fluctuating fields, as compared to estimates existing in literature. We also obse rve a number of qualitatively new phenomena, including a stage of semi classical thermalization, during which the decay of inflaton is essent ially as effective as during the resonance stage.