Measuring the viscosity of dark matter with strongly lensed gravitational waves

TL;DR

This paper proposes a method to measure dark matter's shear viscosity using strongly lensed gravitational waves, potentially revealing dark matter self-interactions at galactic and cluster scales with future GW observatories.

Contribution

It introduces a novel approach to probe dark matter viscosity through GW damping effects in strongly lensed signals, expanding the tools for dark matter characterization.

Findings

Future GW detectors can detect dark matter self-interactions.

Dark matter shear viscosity affects GW propagation in lensing scenarios.

Method could distinguish different dark matter models.

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 gravitational wave domain, i.e., whether a GW experiences the damping effect when it propagates in DM fluid with nonzero shear viscosity. By assuming that the dark matter self-scatterings are efficient enough for the hydrodynamic description to be valid, our results demonstrate that future ground-based Einstein Telescope (ET) and satellite GW observatory (Big Bang Observer; BBO) may succeed in detecting any dark matter self-interactions at the scales of galaxies and clusters.