# Phase Transitions and Baryogenesis From Decays

## TL;DR

This paper investigates how phase transitions in the early universe affect baryogenesis from particle decays, highlighting potential enhancements and challenges in models with symmetry-breaking origins of particle masses.

## Contribution

It provides a detailed analysis of the impact of phase transition types on baryogenesis efficiency, emphasizing the importance of including annihilation effects in such models.

## Key findings

- Second order phase transitions can enhance baryon asymmetry but are fine-tuned.
- Annihilation modes can significantly deplete parent particle abundance.
- Proper modeling requires considering both phase transition effects and annihilation processes.

## Abstract

We study scenarios in which the baryon asymmetry is generated from the decay of a particle whose mass originates from the spontaneous breakdown of a symmetry. This is realized in many models, including low-scale leptogenesis and theories with classical scale invariance. Symmetry breaking in the early universe proceeds through a phase transition that gives the parent particle a time-dependent mass, which provides an additional departure from thermal equilibrium that could modify the efficiency of baryogenesis from out-of-equilibrium decays. We characterize the effects of various types of phase transitions and show that an enhancement in the baryon asymmetry from decays is possible if the phase transition is of the second order, although such models are typically fine-tuned. We also stress the role of new annihilation modes that deplete the parent particle abundance in models realizing such a phase transition, reducing the efficacy of baryogenesis. A proper treatment of baryogenesis in such models therefore requires the inclusion of the effects we study in this paper.