# BBN constraints on the annihilation of MeV-scale dark matter

## TL;DR

This paper evaluates Big Bang Nucleosynthesis (BBN) constraints on MeV-scale dark matter annihilation, showing they are stronger than CMB bounds for p-wave processes and providing a robust lower mass limit.

## Contribution

It provides a detailed analysis of BBN bounds on MeV-scale dark matter annihilation, updating the lower mass limit with improved primordial abundance data.

## Key findings

- BBN constraints are stronger than CMB bounds for p-wave annihilations.
- Updated lower bound on dark matter mass from BBN is more robust than CMB bounds.
- BBN bounds are competitive with other indirect detection methods.

## Abstract

Thermal dark matter at the MeV scale faces stringent bounds from a variety of cosmological probes. Here we perform a detailed evaluation of BBN bounds on the annihilation cross section of dark matter with a mass $1\,\text{MeV} \lesssim m_\chi \lesssim 1\,\text{GeV}$. For $p-wave suppressed annihilations, constraints from BBN turn out to be significantly stronger than the ones from CMB observations, and are competitive with the strongest bounds from other indirect searches. We furthermore update the lower bound from BBN on the mass of thermal dark matter using improved determinations of primordial abundances. While being of similar strength as the corresponding bound from CMB, it is significantly more robust to changes in the particle physics model.