Origin and growth of primordial black holes
  Building on the insight that primordial black holes can arise from the
formation and subsequent gravitational collapse of bound states of stable
supermassive elementary particles during the early radiation era, we offer a
comprehensive picture describing the evolution and growth of the resulting
mini-black holes through both the radiation and matter dominated phases, until
the onset of (small scale) inhomogeneities. This is achieved by means of an
exact metric solving Einstein's equations throughout both phases. We show that,
thanks to a special enhancement effect producing an effective horizon above the
actual event horizon, this process can explain the observed mass values of the
earliest giant black holes. Unlike other proposals, it also predicts a lower
limit on the mass of supermassive black holes.
