Name: Hiroaki Nagao
 Institution: Niigata University
 Title: Non-perturbative Corrections to Particle Production from Coherent Oscillation 
 Key Words: Particle cosmology, Reheating, Coherent oscillation of a scalar field
 Abstract: The coherent oscillation of a scalar field plays a crucial role in various phenomena of particle cosmology. We focus on the reheating process after slow-roll inflation. By neglecting the expansion of the universe, we consider the case where the coupling constants and amplitude of coherent oscillation are sufficiently small. First, we estimate the distribution function of produced particles using the method based on the Bogolyubov transformation. We obtain the analytical expressions for the distribution function and the number density at leading order of couplings. Although these results successfully abstract the characteristic behaviors of yields of produced particles,
we find that, even in the small coupling limit, the nonperturbative corrections of coupling become important in the later times of production. We would like to show that the time averaging method is very useful to handle such corrections analytically.