Kavli Affiliate: Gordan Krnjaic
| First 5 Authors: Ian Holst, Gordan Krnjaic, Huangyu Xiao, ,
| Summary:
If primordial black holes (PBH) are present in the early universe, their
contribution to the energy budget grows relative to that of radiation and
generically becomes dominant unless the initial abundance is exponentially
small. This black hole domination scenario is largely unconstrained for PBHs
with masses $lesssim 10^9,mathrm{g}$, which evaporate prior to Big Bang
nucleosynthesis. However, if the era of PBH domination is sufficiently long,
the PBHs form clusters and can merge appreciably within these objects. We
calculate the population statistics of these clusters within the
Press-Schechter formalism and find that, for a wide range of PBH masses and
Hubble rates at the onset of PBH domination, the mergers within PBH clusters
can exhibit runaway behavior, where the majority of the cluster will eventually
form a single black hole with a mass much greater than the original PBH mass.
These mergers can dramatically alter the PBH mass distribution and leave behind
merged relic black holes that evaporate after Big Bang nucleosynthesis and
yield various observational signatures, excluding parameter choices previously
thought to be viable
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