Long lived MeV scale bound state dark matter alleviates the ${}^7 Li$ tension

Abstract

We investigate the impact of MeV scale unstable bound state dark matter on both thermal and non thermal Big Bang nucleosynthesis. Focusing on the weakly self interacting regime, we find that this framework can reproduce the theoretically predicted abundances through both short and long lived bound states. While long lived bound states can alleviate the cosmological ${}^7$Li problem, they simultaneously lead to discrepancies with other light element abundances. We show that this tension is resolved by incorporating non thermal nucleosynthesis, which act on these non standard initial light element abundances to alleviate the ${}^7 Li$ tension without violating observational constraints on the other elements. Remarkably, across the range of $\widetildeρ_B$ and $m_χ$ considered, long lived bound states with lifetimes $10^0\,{\rm s}\lesssimτ\lesssim10^2\,{\rm s}$ can simultaneously resolve the ${}^7$Li problem and a large parameter space remain consistent with the observed abundances of the other light elements. Our results demonstrate that non thermal effects are essential for obtaining a consistent nucleosynthesis history in unstable bound state dark matter scenarios.