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 non-zero shear viscosity $\eta$ , gravitational waves will be dissipated at a rate proportional to $G \,\eta$. We constrain dark matter and dark energy models with non-zero 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. 
Gaurav Goswami, Girish Kumar Chakravarty, Subhendra Mohanty, A. R.   Prasanna
hep-ph astro-ph.CO gr-qc