Hubble Induced Mass in Radiation Dominated Universe

TL;DR

This paper investigates the effective mass of scalar fields in a radiation-dominated universe within supergravity, revealing that such fields acquire a mass on the order of the Hubble parameter due to thermal effects.

Contribution

It provides a detailed analysis of the scalar field mass in the RD era using Kadanoff-Baym equations, clarifying the thermal average calculation in supergravity.

Findings

Scalar field effective mass is of order H in RD era.

Thermal averaging via Kadanoff-Baym equations is effective.

Results clarify mass behavior post-inflation in supergravity.

Abstract

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 $H$.