BBN constraints on MeV-scale dark sectors. Part II. Electromagnetic decays

TL;DR

This paper investigates how MeV-scale dark sector particles decaying into electrons or photons affect early universe nucleosynthesis, providing constraints on such models and implications for future dark matter detection experiments.

Contribution

It offers a comprehensive analysis of BBN constraints on MeV-scale dark sector particles, especially those with electromagnetic decays, and applies findings to a self-interacting dark matter model.

Findings

Severe constraints on MeV-scale dark particles from BBN considerations.

The model is testable with upcoming low-threshold direct detection experiments.

Dark sector particles significantly influence early universe nucleosynthesis processes.

Abstract

Meta-stable dark sector particles decaying into electrons or photons may non-trivially change the Hubble rate, lead to entropy injection into the thermal bath of Standard Model particles and may also photodisintegrate light nuclei formed in the early universe. We study generic constraints from Big Bang Nucleosynthesis on such a setup, with a particular emphasis on MeV-scale particles which are neither fully relativistic nor non-relativistic during all times relevant for Big Bang Nucleosynthesis. We apply our results to a simple model of self-interacting dark matter with a light scalar mediator. This setup turns out to be severely constrained by these considerations in combination with direct dark matter searches and will be fully tested with the next generation of low-threshold direct detection experiments.