Hubble induced mass in radiation-dominated universe

We reconsider the effective mass of a scalar field which interact with visible sector via Planck-suppressed coupling in supergravity framework. We focus on the radiation-dominated (RD) era after inflation. In this era, the effective mass is given by thermal average of interaction terms. To make our analysis clear, we rely on Kadanoff–Baym equations to evaluate the thermal average. We find that, in RD era, a scalar field acquires the effective mass of the order of H.