Primordial Black Hole Scenario for the Gravitational-Wave Event GW150914
  We point out that the gravitational-wave event GW150914 observed by the LIGO
detectors can be explained by the coalescence of primordial black holes (PBHs).
It is found that the expected PBH merger rate would exceed the rate estimated
by the LIGO scientific Collaboration and Virgo Collaboration if PBHs were the
dominant component of dark matter, while it can be made compatible if PBHs
constitute a fraction of dark matter. Intriguingly, the abundance of PBHs
required to explain the suggested lower bound on the event rate, $> 2$ events
${\rm Gpc}^{-3} {\rm yr}^{-1}$, roughly coincides with the existing upper limit
set by the nondetection of the cosmic microwave background spectral distortion.
This implies that the proposed PBH scenario may be tested in the
not-too-distant future.
