Constraining Mixed Dark-Matter Scenarios of WIMPs and Primordial Black
  Holes from CMB and 21-cm observations
  We consider the dark matter (DM) scenarios consisting of the mixture of WIMPs
and PBHs and study how much 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 the stringent bounds on the allowed PBH
fraction which are comparable or even tighter than those from the gamma ray
data depending on the DM masses. For instance, the MCMC likelihood analysis
using the Planck CMB data leads to the bound on PBH DM fraction with respect to
the total dark matter $f_{\rm PBH} \lesssim {\cal O}( 10^{-10}\sim 10^{-8})$
for the WIMP mass $m_{\chi}\sim {\cal O}(10\sim 10^3)$ GeV with the
conventional DM annihilation cross section $\langle \sigma v \rangle=3 \times
10^{-26}~\rm cm^3/s $. We also investigate the feasibility of the global 21-cm
signal measurement to provide the stringent constraints on the PBH fraction.
