Asymmetric dark matter and effective number of neutrinos

TL;DR

This paper investigates how MeV-scale asymmetric dark matter interactions influence the effective number of neutrinos during big bang nucleosynthesis, providing new constraints on dark matter mass based on neutrino coupling strengths.

Contribution

It introduces a study of asymmetric dark matter effects on $N_{eff}$ at BBN, highlighting the impact of coupling strength differences on dark matter mass limits.

Findings

Lower mass limit of about 18 MeV for dark matter with certain coupling conditions

Dark matter coupling to neutrinos significantly affects $N_{eff}$

Constraints depend on the relative interaction rates with neutrinos versus photons/electrons

Abstract

We study the effect of the MeV-scale asymmetric dark matter annihilation on the effective number of neutrinos $N_{\rm eff}$ at the epoch of the big bang nucleosynthesis. If the asymmetric dark matter $\chi$ couples more strongly to the neutrinos $\nu$ than to the photons $\gamma$ and electrons $e^-$, $\Gamma_{\chi\gamma, \chi e} \ll \Gamma_{\chi\nu}$, or $\Gamma_{\chi\gamma, \chi e} \gg \Gamma_{\chi\nu}$, the lower mass limit on the asymmetric dark matter is about $18$ MeV for $N_{\rm eff}\simeq 3.0$.