Gravitational waves from primordial black holes collisions in binary
  systems
  It was shown by (Nakamura et al. 1997), (Ioka et al. 1998), and (Sasaki et
al. 2016) that primordial black holes (PBHs) binaries can form effectively at
the cosmological stage of radiation dominance, and the merge of the PBHs in
pairs can explain the gravitational wave burst GW150914. In this paper, the
model is re-examined by considering the effect of inflationary dark matter
density perturbations which produce additional tidal forces. As a result, the
merge rate of PBHs binaries and the corresponding rate of the gravitational
bursts are suppressed by the factor $\sim1.5-2$ in comparison with previous
calculations. This rate matches the LIGO data if the PBHs constitute the
$f\sim5\times10^{-4}-5\times10^{-3}$ fraction of dark matter.
