Abstract
Primordial black hole (PBH) dark matter (DM) non-linear small-scale structure
formation begins before the epoch of recombination due to large Poisson density
fluctuations. Those small-scale effects survive until today, distinguishing
physics of PBH DM structure formation from the one involving WIMP DM. We
construct an analytic model for the small-scale PBH velocities which reproduces
the velocity floor seen in numerical simulations, and investigate how these
motions impact PBH accretion bounds at different redshifts. We find that the
effect is small at the time of recombination, leaving the CMB bounds on PBH
abundance unchanged. However, already at $z=20$ the PBH internal motion
significantly reduces their accretion due to the additional $1/v^6$
suppression, affecting the 21 cm bounds. Today the accretion bounds arising
from dwarf galaxies or smaller PBH sub-structures are all reduced by the PBH
velocity floor. We also investigate the feasibility for the PBH clusters to
coherently accrete gas leading to a possible enhancement proportional to the
cluster's occupation number but find this effect to be insignificant for PBH
around $10 M_ødot$ or lighter. Those results should be reconsidered if the
initial PBH distribution is not Poisson, for example, in the case of large
initial PBH clustering.
Users
Please
log in to take part in the discussion (add own reviews or comments).