Small-scale structure of primordial black hole dark matter and its implications for accretion

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 10M 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. arXiv:1907.06533v1 [astro-ph.CO]

From primordial black holes abundance to primordial curvature power spectrum (and back)

“…Given the interest in this potential dark matter candidate and the rich phenomenology of black holes, a large number of observational constraints on the abundance of PBHs have been obtained so far. They cover a remarkable portion of the allowed mass range and they include constraints coming from gravitational lensing effects [28][29][30][31][32][33][34][35][36], dynamical effects [37][38][39][40][41][42][43][44][45][46][47][48], accretion effects [49][50][51][52][53][54][55][56][57] and effects on large-scale structure [58,59]. Two mass ranges remain still open, around 10 −15 M and 10 −12 M .…”

GW190521 Mass Gap Event and the Primordial Black Hole Scenario

“…[5] for a review), and that can comprise a significant fraction f PBH of the dark matter (DM) [6,7]. The possible primordial origin of at least some of the GW events has motivated several studies on the confrontation between the PBH scenario and the GW data [6][7][8][9][10][11][12][13][14][15].…”

“…This effect is included in the parameter λ [47]. We account for the sharp decrease in the accretion efficiency around the epoch of structure formation [9,11,53] and for other uncertainties in the model (such as x-ray preheating [54], details of the structure formation and feedbacks of local, global [49,55], and mechanical type [56]) by setting a cutoff redshift z cutoff ¼ 10 after which we neglect accretion. Based on previous detailed investigation [39,47], we consider z cutoff ¼ 10 as a benchmark case to study the impact of accretion on the PBH scenario.…”

Cosmological black holes are not described by the Thakurta metric: LIGO-Virgo bounds on PBHs remain unchanged

“…[24], the mass differences are milder as mass growth should stop once virialized DM halo absorbs the TCOs because the Thakurta metric does not apply in such environments. The postulated effect can be softened further if TCOs make up most of DM, since then the first virialized structures can form already around matter-radiation equality [5,[30][31][32]. By a similar argument, Eq.…”