Impacts of new small-scale N-body simulations on dark matter annihilations constrained from cosmological 21cm line observations

Abstract

We revisit constraints on annihilating dark matter based on the global 21cm signature observed by EDGES. For this purpose, we used the numerical data of the latest N-body simulation performed by state-of-the-art standard in order to estimate the boost factor at high redshifts ($z$ = 10 - 100), which enhances the annihilation of dark matter in course of structure formation. By taking into account to what fraction injected energy from dark matter annihilation contributes to ionization, excitation and heating of intergalactic medium during dark ages, we estimated how large the global 21cm absorption can be. By assuming the thermal freezeout scenario, we find that $m_{\rm DM} < 15$ GeV and $m_{\rm DM} < 3$ GeV have been excluded at 95$\%$ C.L. for the annihilation modes into $b\bar{b}$ and $e^+ e^-$, respectively.