Revisiting Primordial Black Holes Constraints from Ionization History
  Much attention has been drawn to the recent discoveries by the Advanced Laser
Interferometer Gravitational-Wave Observatory (LIGO) of merging intermediate
mass black holes. Of particular interest is the possibility that the merger
events detected could be evidence of dark matter in the form of primordial
black holes (PBHs). It has been argued that the presence of many black holes
would effect the thermal and ionization history of the universe via their
accretion of matter which would have strong signatures in the Cosmic Microwave
Background's (CMB) power spectra evident in the damping of anisotropies and
change in low-$l$ polarization power. In general the accretion is quite
sensitive to the specific physics involved and the conditions of the early
universe. In this work, we take a minimal approach and find constraints on PBHs
not including the model dependent effects of nonlinear structure of formation
or transition between different accretion models which would work to increase
the effect. In addition, we include the relative velocity between dark matter
and baryonic matter including the effects of supersonic streaming at high
redshift which work to significantly reduce the constraining power. We also
examine the constraints on more astrophysically-motivated extended black hole
mass functions and discuss how mergers might effect this distribution. We find
constraints on PBHs in the range $ \approx 30 M_\odot$, finding that they could
not compose more than $10\%$ of the total dark matter content.
