Formation and Clustering of Primordial Black Holes in Brans-Dicke Theory

Abstract

The formation of primordial black holes in the early universe in the Brans-Dicke scalar-tensor theory of gravity is investigated. Corrections to the threshold value of density perturbations are found. Above the threshold, the gravitational collapse occurs after the cosmological horizon crossing. The corrections depend in a certain way on the evolving scalar field. They affect the probability of primordial black holes formation, and can lead to their clustering at large scales if the scalar field is inhomogeneous. The formation of the clusters, in turn, increases the probability of black holes merge and the corresponding rate of gravitational wave bursts. The clusters can provide a significant contribution to the LIGO/Virgo gravitational wave events, if part of the observed events are associated with primordial black holes.

Mechanisms of Producing Primordial Black Holes and Their Evolution

“…At the moment, constraints are imposed on a wide range of masses of a PBH as a dark matter candidate [11]. It has also been shown [12][13][14] that primordial black hole formation mechanisms are able to form clusters of PBHs and then, some constraints imposed on black holes as dark matter candidates should be reconsidered [13,15,16].…”

Editorial to the Special Issue “Selected Papers from the 17th Russian Gravitational Conference—International Conference on Gravitation, Cosmology and Astrophysics (RUSGRAV-17)”

“…Scale-dependent gravity in the superfluid vacuum theory is considered in [26] as a possible alternative to dark matter and dark energy. Three articles are devoted to quark stars in massive Brans-Dicke gravity with Tolman-Kuchowicz spacetime [27], non-relativistic limit of embedding gravity as general relativity with dark matter [28], and to the formation and clustering of primordial black holes in Brans-Dicke theory [29]. The hybrid metric-Palatini gravity in the case of regular stringlike configurations and gravity with higher derivatives in D-dimensions are discussed in [30,31], respectively.…”