Exploiting the Einstein Telescope to solve the Hubble tension

Abstract: We probe four cosmological models which, potentially, can solve the Hubble tension according to the dark energy equation of state. In this context, we demonstrate that the Einstein Telescope is capable of achieving a relative accuracy below $1\%$ on the Hubble constant independently of the specific dark energy model. We firstly build mock catalogs containing gravitational wave events for one, five and ten years of observations, and above Signal-to-Noise Ratio equal to nine. From these catalogs, we extract the events which are most likely associated with possible electromagnetic counterpart detected by THESEUS. Finally, we select four dark energy models, namely a non-flat $\omega$CDM, an interacting dark energy, an emergent dark energy, and a time varying gravitational constant model, to forecast the precision down to which the Einstein Telescope can bound the corresponding cosmological parameters. We foresee that the Hubble constant is always constrained with less than $1\%$ uncertainty, thereby offering a potential solution to the Hubble tension. The accuracy on the other cosmological parameters is at most comparable with the one currently obtained using multiple probes, except for the emergent dark energy model for which the Einstein Telescope alone will be able to improve the current limits by more than one order of magnitude.