The inflaton must convert its energy into radiation after inflation, which, in a conventional scenario, is caused by the perturbative decay of inflaton.

However, the process of reheating would be much more complicated in some cases, since the decay products obtain masses from an oscillating inflaton and thermal environment. Hence, the conventional reheating scenario where the reheating takes place via the perturbative decay of inflaton can be modified. We study in detail processes of reheating: non-perturbative particle production from the inflaton and the subsequent evolution of inflaton/plasma system by taking account for the thermal dissipation of inflaton in a hot plasma.

In this talk, at first, I would like to explain general aspects of dynamics of oscillating scalar field in the early universe, and then, move on to its application to the reheating after inflation. In particular, I will show that the reheating temperature is significantly affected by the thermal dissipation; especially the deviation from the conventional reheating scenario becomes prominent for smaller inflaton mass.