  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 $H$.
