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arXiv · 2106.07122

Simple estimate of BBN sensitivity to light freeze-in dark matter

Shao-Ping Li·Xin-Qiang Li·Xin-Shuai Yan·Ya-Dong Yang
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Abstract

We provide a simple analysis of the big-bang nucleosynthesis (BBN) sensitivity to the light dark matter (DM) generated by the thermal freeze-in mechanism. It is shown that the ratio of the effective neutrino number shift $ΔN_ν$ over the DM relic density $ω\equiv Ωh^2$, denoted by $R_χ\equivΔN_ν/ω$, cancels the decaying particle mass and the feeble coupling, rendering therefore a simple visualization of $ΔN_ν$ at the BBN epoch in terms of the DM mass. This property drives one to conclude that the shift with a sensitivity of $ΔN_ν\simeq \mathcal{O}(0.1)$ cannot originate from a single warm DM under the Lyman-$α$ forest constraints. For the cold-plus-warm DM scenarios where the Lyman-$α$ constraints are diluted, the ratio $R_χ$ can be potentially used to test the thermal freeze-in mechanism in generating a small warm component of DM and a possible excess at the level of $ΔN_ν\simeq \mathcal{O}(0.01)$.

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Shao-Ping Li, Xin-Qiang Li, Xin-Shuai Yan, Ya-Dong Yang. 2021-12-08. Simple estimate of BBN sensitivity to light freeze-in dark matter. https://doi.org/10.1103/physrevd.104.115007

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