Constraining mixed dark-matter scenarios of WIMPs and primordial black holes from CMB and 21-cm observations

Abstract

We consider the dark-matter (DM) scenarios consisting of the mixture of weakly interacting massive particles (WIMPs) and primordial black holes (PBHs) and study what fraction of the total DM can be PBHs. In such scenarios, PBHs can accrete the WIMPs and consequently enhance the heating and ionization in the intergalactic medium due to WIMP annihilations. We demonstrate that the CMB data can give stringent bounds on the allowed PBH fraction which are comparable to or even tighter than those from the gamma-ray data depending on the DM masses. For instance, the Markov-chain Monte Carlo likelihood analysis using the Planck CMB data leads to a bound on the PBH DM fraction with respect to the total dark matter ${f}_{\mathrm{PBH}}\ensuremath{\lesssim}\mathcal{O}({10}^{\ensuremath{-}10}\ensuremath{\sim}{10}^{\ensuremath{-}8})$ for the WIMP mass ${m}_{\ensuremath{\chi}}\ensuremath{\sim}\mathcal{O}(10\ensuremath{\sim}{10}^{3})\text{ }\text{ }\mathrm{GeV}$ with the conventional DM annihilation cross section $⟨\ensuremath{\sigma}v⟩=3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}26}\text{ }\text{ }{\mathrm{c}\mathrm{m}}^{3}/\mathrm{s}$. We also investigate the feasibility of the global 21-cm signal measurement to provide stringent constraints on the PBH fraction.