Radio bounds on the mixed dark matter scenarios of primordial black
  holes and WIMPs
  We study the synchrotron radio emission in the mixed dark matter scenarios
consisting of the primordial black holes (PBHs) and the self-annihilating WIMPs
(weakly interacting massive particles). The WIMPs can form the ultracompact
minihalos around PBHs and the annihilation enhancement from these dense halos
can lead to the efficient synchrotron radiation at the radio frequency in the
presence of galactic magnetic fields. The upper bound of PBH fraction with
respect to the total dark matter abundance is of order $10^{-8}\sim 10^{-5}$
depending on the electroweak scale WIMP mass ($m_{\chi}=10\sim 1000$ GeV) and
the WIMP annihilation channel (e.g. a hadronic $\chi \chi \rightarrow b
\bar{b}$ or a leptonic $\chi \chi \rightarrow e^+ e^-$ channel). The PBH
contribution to the total dark matter abundance is hence negligible when the
other component of dark matter is composed of the conventional electroweak
scale WIMPs.
