Constraints on Compact Dark Matter from the Nonobservation of Gravitational-wave Strong Lensing

Abstract We use the nonobservation of strong lensing of gravitational waves (GWs) in the first three observation runs of the LIGO and Virgo detectors to constrain the fraction of dark matter in the form of compact objects (COs) in the mass range 10 6 −10 9 M ⊙ . Using a Bayesian formalism supplemented by astrophysical simulations of strong lensing of GWs, we constrain the compact dark matter fraction to ≲0.4−0.6 with currently available data and show that they may get significantly tighter in the future. We find that multiple lensing—i.e., GWs getting deflected by multiple COs on their way to us—is possible. By ignoring this, we underestimate the constraints by a few percent.