Measuring the viscosity of dark matter with strongly lensed gravitational waves

Abstract

ABSTRACT Based on the strongly lensed gravitational waves (GWs) from compact binary coalescence, we propose a new strategy to examine the fluid shear viscosity of dark matter (DM) in the GW domain, i.e. whether a GW experiences the damping effect when it propagates in DM fluid with nonzero shear viscosity. By assuming that the DM self-scatterings are efficient enough for the hydrodynamic description to be valid, our results demonstrate that future ground-based Einstein Telescope and satellite GW observatory (big bang observer) may succeed in detecting any DM self-interactions at the scales of galaxies and clusters.