Bayesian analysis of a Unified Dark Matter model with transition: can it alleviate the H_0 tension?

We consider cosmological models in which Dark Matter (DM) and Dark Energy (DE) are described by a single component, dubbed Unified Dark Matter (UDM) models, in which the DE-like part can have an equation state <-1 at late times without violating the null energy condition. In this paper, we investigate whether this feature can relieve the Hubble tension. We perform a Bayesian analysis of the model using SNIa data from Pantheon, the CMB distance prior from Planck, and the prior on the absolute magnitude M of SNIa from SH0ES. Using the prior, the data suggests a smooth transition taking place at redshifts z_ t≃ 2.85, which provides a value H_0=69.64± 0.88 for the Hubble constant, slightly alleviating the tension by ∼ 1.5 σ. Without it, we obtain H_0 = 67.6^+1.3_-0.82 and a transition happening at z_t=1.36. We also discuss the importance of using the prior on M for constraining this model.