Probing interacting dark sector with the next generation of gravitational-wave detectors

We probed the capability of third-generation gravitational wave (GW) interferometers, such as the Einstein Telescope and Cosmic Explorer, to constrain a cosmological model with an interacting dark sector. We focused on GW events with a detected electromagnetic counterpart being the gamma or x emission of gammaray burst, and a kilonova emission. We assumed that the first one is detected by the THESEUS satellite while the second one is detected by the Vera Rubin Observatory. We probed three different interaction kernels and found that the posterior estimation of the cosmological parameters is biased due to the existing degeneracies between the dark and matter sectors. We also found that introducing an external prior on the matter density parameter breaks the degeneracy, removes the bias results, and improves the accuracy on the dark sector parameters.