Cosmological Particle Decays at Finite Temperature

TL;DR

This paper calculates how finite temperature environments affect the decay rates of neutral scalar particles, revealing significant thermal effects in cosmological contexts, especially when particles are nonrelativistic and lighter than the background temperature.

Contribution

It provides a detailed computation of finite-temperature corrections to decay rates of scalar particles, highlighting conditions where thermal effects are most significant.

Findings

Thermal effects are largest when particles are nonrelativistic and lighter than the background temperature.

Finite-temperature decay rates can differ substantially from zero-temperature rates under certain cosmological conditions.

Thermal effects diminish when the decaying particle has nonzero momentum.

Abstract

We calculate finite-temperature corrections to the decay rate of a generic neutral (pseudo)scalar particle that decays into (pseudo)scalars or fermion-antifermion pairs. The ratio of the finite-temperature decay rate to the zero-temperature decay rate is presented. Thermal effects are largest in the limit where the decaying particle is nonrelativistic but with a mass well below the background temperature, but significant effects are possible even when we relax the former assumption. Thermal effects are reduced for the case of nonzero momentum of the decaying particle. We discuss cosmological scenarios under which significant finite-temperature corrections to the decay rate can be achieved.