Lensing by primordial black holes: Constraints from gravitational wave observations

Abstract

Primordial black holes (PBHs) have been proposed to explain at least a portion of dark matter. Observations have put strong constraints on PBHs in terms of the fraction of dark matter which they can represent, fPBH, across a wide mass range – apart from the stellar-mass range of 20M⊙ ∼ MPBH ∼ 100M⊙. In this paper, we explore the possibility that such PBHs could serve as pointmass lenses capable of altering the gravitational-wave (GW) signals observed from binary black hole (BBH) mergers along their line-of-sight. We find that careful GW data analysis could verify the existence of such PBHs based on the fitting factor and odds ratio analyses. When such a lensed GW signal is detected, we expect to be able to measure the redshifted mass of the lens with a relative error ∆MPBH/MPBH ∼ 0.3. If no such lensed GW events were detected despite the operation of sensitive GW detectors accumulating large numbers of BBH mergers, it would translate into a stringent constraint of fPBH ∼ 10 −2 − 10 for PBHs with a mass larger than ∼ 10M⊙ by the Einstein Telescope after one year of running, and fPBH ∼ 0.2 for PBHs with mass greater than ∼ 50M⊙ for advanced LIGO after ten years of running.