Microlensing of gravitational waves by dark matter structures by Malcolm Fairbairn et al. on Wednesday 30 November

Gravitational lensing of gravitational waves provides a potential new probe

of dark matter structures. In this work, we consider the microlensing effect on

gravitational wave signals from black hole binaries induced by low-mass dark

matter halos that do not retain enough baryonic matter to hold stars. We

clarify systematically when this microlensing effect is relevant and study in

detail its detectability by future gravitational wave observatories. We

consider lensing by cold dark matter halos and by solitonic cores that reside

in fuzzy dark matter halos. Our results show that although the effect can be

detectable at relatively large impact parameters, the probability of detecting

such lensed events is low. In particular, we find that the expected number of

events lensed by cold dark matter halos is $\mathcal{O}(0.01)$ per year for BBO

and the expected number of events lensed by solitonic cores inside fuzzy dark

matter halos is $\mathcal{O}(0.01)$ per year for ET. In the case that a

significant fraction of dark matter consists of $\mathcal{O}(100 M_\odot)$

objects that are relatively compact, $R < \mathcal{O}(0.1\,{\rm pc})$, we show

that the expected number of lensed events per year ET can be very large,

$\mathcal{O}(1000)$.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2210.13436v2