Note on the thermal history of decoupled massive particles

TL;DR

This paper presents a simplified and more general method for analyzing the thermal history and momentum decay of decoupled massive particles, improving upon previous approaches.

Contribution

It introduces a simpler, more general strategy for studying the thermal evolution of decoupled massive particles compared to prior methods.

Findings

Simplified approach to momentum decay analysis

More general results for thermal evolution

Applicable to a wider range of particle scenarios

Abstract

This note provides an alternative approach to the momentum decay and thermal evolution of decoupled massive particles. Although the ingredients in our results have been addressed in Ref.\cite{Weinberg}, the strategies employed here are simpler, and the results obtained here are more general.