# The Thermal History of Composite Dark Matter

## TL;DR

This paper investigates the thermal evolution of composite Dark Matter models, analyzing how symmetries, interactions, and plasma decay influence relic abundance and experimental detectability.

## Contribution

It introduces an analytic formalism for calculating relic densities and explores the effects of various interactions and entropy changes on dark matter evolution.

## Key findings

- Dark relic density can be diluted by entropy from plasma decay
- Indirect detection experiments are promising for testing these models
- The relative strength of interactions determines the thermal fate of composite dark matter

## Abstract

We study the thermodynamic history of composite Dark Matter models. We start with classifying the models by means of the symmetries partially protecting the composite Dark Matter decays and constrain their lifetimes. For each model, we determine the impact of number-changing and number-conserving operators on its thermal history. We also develop the analytic formalism to calculate the asymptotic abundance of stable relics. We show how the relative strength between number-changing and number-conserving interactions together with the dark plasma lifetime affect the thermal fate of the various composite models. Additionally, we discover that the final dark relic density of composite particles can be diluted due to an entropy increase stemming from dark plasma decay. Finally, we confront the models with experimental bounds. We find that indirect detection experiments are most promising in testing this large class of models.