Listening to the sound of dark sector interactions with gravitational wave standard sirens

Abstract: We consider two stable Interacting Dark Matter -- Dark Energy models and confront them against current Cosmic Microwave Background data from the \textit{Planck} satellite. We then generate luminosity distance measurements from ${\cal O}(10^3)$ mock Gravitational Wave events matching the expected sensitivity of the proposed Einstein Telescope. We use these to forecast how the addition of Gravitational Wave standard sirens data can improve current limits on the Dark Matter -- Dark Energy coupling strength ($\xi$). We find that the addition of Gravitational Waves data can reduce the current uncertainty by a factor of $5$. Moreover, if the underlying cosmological model truly features Dark Matter -- Dark Energy interactions with a value of $\xi$ within the currently allowed $1\sigma$ upper limit, the addition of Gravitational Wave data would help disentangle such an interaction from the standard case of no interaction at a significance of more than $3\sigma$.