Ultracompact minihalos associated with stellar-mass primordial black holes

Abstract

The possibility that primordial black hole binary mergers of stellar mass can explain the signals detected by the gravitational-wave interferometers has attracted much attention. In this scenario, primordial black holes can comprise only part of the entire dark matter, say, of order 0.1 %. This implies that most of the dark matter is accounted for by a different component, such as Weakly Interacting Massive Particles. We point out that in this situation, very compact dark matter minihalos, composed of the dominant component of the dark matter, are likely to be formed abundantly in the early Universe, with their formation redshift and abundance depending on primordial non-Gaussianity. They may be detected in future experiments via pulsar observations.

Gravitational wave probes of dark matter: challenges and opportunities

“…In scenarios where PBHs are formed from enhanced primordial perturbations (Sec. II A), the same rare, large density fluctuations which produce PBHs should also lead to the formation of gravitationally bound ultra-compact mini-halos (UCMHs) of particle DM [77,[89][90][91][92]. This in turn would lead to enhanced lensing and annihilation signatures due to these UCMHs (see e.g.…”

Pulsar timing array constraints on the induced gravitational waves

“…However, the curvature perturbation on small scales is unknown, because the resolution of the CMB experiments is limited, and the other observations are not so accurate. Substantial primordial black holes (PBHs) can be the seeds for galaxy formation [28][29][30][31], the dark matter candidate [32][33][34][35][36], or the sources of LIGO/VIRGO detection, depending on their masses and abundance at formation, which can be constrained by PBH remnants that survive Hawking radiation, star-capture processes, microlensing, CMB µ-distortion, and so on.…”

The Gravitational-wave physics II: Progress

“…For instance, the LIGO O3a data set of LIGO/Virgo implies that there might be two populations of black holes [346], which can be explained by the combination of the astrophysical black holes and PBHs of ∼20 solar mass [347][348][349]. PBHs might be the supermassive or stupendously large BHs which seed the galaxy or even structure formation [350][351][352][353][354][355][356]. The planetary-mass PBHs could be the lensing objects of the microlensing events observed by the Optical Gravitational Lensing Experiment (OGLE) [357][358][359][360], or even the Planet 9 [361].…”