Lensing of gravitational waves as a probe of compact dark matter

TL;DR

This paper investigates how gravitational lensing of gravitational waves can be used to constrain the abundance of compact dark matter objects like primordial black holes, using data from LIGO-Virgo and future detectors.

Contribution

It provides a method to estimate lensing detectability in gravitational wave signals and derives new constraints on the fraction of dark matter in compact objects based on non-observation of lensing events.

Findings

LIGO-Virgo data excludes all dark matter as compact objects above 200 solar masses.

Less than 40% of dark matter can be in objects above 400 solar masses.

Future detectors can probe dark matter fractions as low as 7×10⁻⁵ for objects above 40 solar masses.

Abstract

We study gravitational lensing of gravitational waves from compact object binaries as a probe of compact dark matter (DM) objects such as primordial black holes. Assuming a point mass lens, we perform parameter estimation of lensed gravitational wave signals from compact object binaries to determine the detectability of the lens with ground based laser interferometers. Then, considering binary populations that LIGO-Virgo has been probing, we derive a constraint on the abundance of compact DM from non-observation of lensed events. We find that the LIGO-Virgo observations imply that compact objects heavier than $M_l = 200M_\odot$ can not constitute all DM and less than $40\%$ of DM can be in compact objects heavier than $M_l = 400M_\odot$. We also show that the DM fraction in compact objects can be probed by LIGO in its final sensitivity for $M_l > 40M_\odot$ reaching $2\%$ of the DM abundance at $M_l > 200M_\odot$, and by ET for $M_l > 1M_\odot$ reaching DM fraction as low as $7\times 10^{-5}$ at $M_l > 40M_\odot$.