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

We revisit constraints on annihilating dark matter based on the cosmological global 21 cm signature observed by EDGES. For this purpose, we used the numerical data of the latest $N$-body simulation for the first time 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 formations. 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 21 cm absorption can be. In the thermal freeze-out scenario, we find that the dark matter masses $m_{\mathrm{DM}}<15\mathrm{GeV}$ and $m_{\mathrm{DM}}<3\mathrm{GeV}$ have been excluded at 95% C.L. for the modes into $b\overline{b}$ and $e^{+}{e}^{-}$, respectively, which are obtained independently of any uncertainties in local astrophysics such as observationally-fitted density profiles of dark matter halos.

Figure 1

Boost factors computed from linear perturbation calculations (orange dotted) and the $N$-body simulations (blue solid) done in Ref. [4]. For reference, we also depict $B(z)$ based on the halo model in [53], which is referred to as the “Boost 1” model in [6] (green dashed).

Figure 2

Evolution of $x_e$ and $T_m$ in the presence of DM annihilation. From top left to bottom right, cases of annihilation channels into $W^{+}{W}^{-}$, $b\overline{b}$, $e^{+}{e}^{-}$, $\gamma \gamma$ are plotted. The DM mass $m_{\mathrm{DM}}$ is assumed to be 100 GeV. Annihilation cross section $⟨\sigma v⟩$ is taken to be $3\times {10}^{-24}$ (red), $3\times {10}^{-25}$ (green), $3\times {10}^{-26}$ (blue) and $3\times {10}^{-27}$ (magenta). The boost factor $B(z)$ is computed based on the $N$-body simulation (solid) and the linear perturbation theory (dotted). For reference, $T_{\gamma }(z)$ (black dashed) is also plotted in each panel of $T_m(z)$.

Figure 3

Constraints on DM annihilation cross section for the modes into $W^{+}{W}^{-}$ (blue), $b\overline{b}$ (orange), $e^{+}{e}^{-}$ (green) and $\gamma \gamma$ (orange). We here put the upper bound by assuming $T_{21\mathrm{cm}}\le -75\mathrm{mK}$ corresponding to $2\sigma$ deviation from the baseline. The canonical WIMP cross section $⟨\sigma v⟩=2\times {10}^{-26}{\mathrm{cm}}^3/\sec$ is also shown for reference (black solid line).