Seven Hints for Primordial Black Hole Dark Matter
  Seven observations point towards the existence of primordial black holes
(PBH), constituting the whole or an important fraction of the dark matter in
the Universe: the mass and spin of black holes detected by Advanced LIGO/VIRGO,
the detection of micro-lensing events of distant quasars and stars in M31, the
non-detection of ultra-faint dwarf satellite galaxies with radius below 15
parsecs, evidences for core galactic dark matter profiles, the correlation
between X-ray and infrared cosmic backgrounds, and the existence of
super-massive black holes very early in the Universe's history. Some of these
hints are newly identified and they are all intriguingly compatible with the
re-constructed broad PBH mass distribution from LIGO events, peaking on PBH
mass $m_{\rm PBH} \approx 3 M_\odot$ and passing all other constraints on PBH
abundances. PBH dark matter also provides a new mechanism to explain the
mass-to-light ratios of dwarf galaxies, including the recent detection of a
diffuse galaxy not dominated by dark matter. Finally we conjecture that between
0.1% and 1% of the events detected by LIGO will involve a PBH with a mass below
the Chandrasekhar mass, which would unambiguously prove the existence of PBH.
