Early structure formation in primordial black hole cosmologies

Abstract

Cold dark matter (CDM) could be composed of primordial black holes (PBH) in addition to or instead of more orthodox weakly interacting massive particle dark matter (PDM). We study the formation of the first structures in such ΛPBH cosmologies using N -body simulations evolved from deep in the radiation era to redshift 99. When PBH are only a small component of the CDM, they are clothed by PDM to form isolated halos. On the other hand, when PBH make most of the CDM, halos can also grow via clustering of many PBH. We find that the halo mass function is well modelled via Poisson statistics assuming random initial conditions. We quantify the nonlinear velocities induced by structure formation and find that they are too small to significantly impact CMB constraints. A chief challenge is how best to extrapolate our results to lower redshifts relevant for some observational constraints.

Bayesian analysis of LIGO-Virgo mergers: Primordial versus astrophysical black hole populations

“…Some of the uncertainty in the precise formation mechanism is bracketed by the cases S = 1 and the full expressions of Equations ( 8) and (9). More precise numerical simulations of PBH binary formation and evolution will be required for a more quantitative investigation of the sensitivity of our results to the formation model [15,[52][53][54][55].…”

“…Ref. [48] showed that the DM halo which forms around PBHs [52,57] has minimal impact on the merger rate and the estimate of f PBH . Accretion onto a PBH can increase the initially negligible spin of a PBH, provided that the PBH mass grows significantly [41].…”

Extreme primordial black holes

“…These small-scale effects include large PBH velocity dispersion, accretion, and clustering effects seen in previous numerical investigations (e.g. Hütsi et al (2019); Inman & Ali-Haïmoud (2019)). These effects will weaken the validity of the upper bounds on f pbh at such small scales.…”

New horizons in cosmology with spectral distortions of the cosmic microwave background

“…However, if large non-Gaussian curvature perturbation were created at the relevant small scales (not probed by CMB anisotropies), the above bound could become much milder [228]. In this case, PBH clusters would be expected (e.g., [229]), which could furthermore lead to anisotropic distortion signals. Future measurements of CMB spectral distortions could shed further light on these scenarios.…”