Constraints on cosmological viscosity and self-interacting dark matter from gravitational wave observations

It has been shown that gravitational waves propagate through ideal fluids without experiencing any dispersion or dissipation. However, if the medium has a nonzero shear viscosity η, gravitational waves will be dissipated at a rate proportional to Gη. We constrain dark matter and dark energy models with nonzero shear viscosity by calculating the dissipation of gravitational waves from GW150914 which propagate over a distance of 410 Mpc through the dissipative fluid and comparing the data with the theoretical prediction. This provides a proof-of-principle demonstration of the fact that future observations gravitational waves at LIGO have the potential of better constraining the viscosity of dark matter and dark energy.