Gravitational waves from primordial black holes collisions in binary systems

TL;DR

This paper re-examines primordial black hole binary mergers as sources of gravitational waves, accounting for inflationary dark matter perturbations, and finds that merger rates are suppressed but still consistent with LIGO observations for a small dark matter fraction.

Contribution

It introduces the effect of inflationary dark matter perturbations on PBH binary merger rates, refining previous models and aligning predictions with LIGO data.

Findings

Merger rate is suppressed by a factor of 1.5-2 due to dark matter perturbations.

PBHs can explain LIGO gravitational wave events with a dark matter fraction of 5×10⁻⁴ to 5×10⁻³.

The revised model aligns PBH merger predictions with observed gravitational wave data.

Abstract

It was shown by (Nakamura et al. 1997), (Ioka et al. 1998), and (Sasaki et al. 2016) that primordial black holes (PBHs) binaries can form effectively at the cosmological stage of radiation dominance, and the merge of the PBHs in pairs can explain the gravitational wave burst GW150914. In this paper, the model is re-examined by considering the effect of inflationary dark matter density perturbations which produce additional tidal forces. As a result, the merge rate of PBHs binaries and the corresponding rate of the gravitational bursts are suppressed by the factor $\sim1.5-2$ in comparison with previous calculations. This rate matches the LIGO data if the PBHs constitute the $f\sim5\times10^{-4}-5\times10^{-3}$ fraction of dark matter.