Radio bounds on the mixed dark matter scenarios of primordial black holes and WIMPs

Abstract

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.