Primordial Black Hole as a Source of the Boost Factor
  Primordial black holes (PBHs) accumulate weakly interacting massive particles
(WIMPs) around them and form ultracompact minihalos (UCMHs), if the WIMP is a
dominant component of the dark matter (DM). In this paper, we discuss that the
UCMHs seeded by the PBHs with sub-earth mass enhance the WIMP annihilation in
the present Universe and can successfully explain the positron and/or electron
excess in cosmic ray observed by PAMELA/Fermi experiments. The signal is very
similar to that from a decaying dark matter, which can explain the PAMELA
and/or Fermi anomaly without conflict with any constraints as long as the decay
mode is proper. In this scenario, the boost factor can be as large as 10^5. In
addition, we discuss testability of our scenario by gamma-ray point source and
gravitational-wave experiments.
