Bayesian analysis of a Unified Dark Matter model with transition: can it alleviate the H0 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 zt ≃ 2.85, which provides a value H0 = 69.64 ± 0.88 for the Hubble constant, slightly alleviating the tension by ∼1.5σ. Without it, we obtain H0 = 67.6+1.3 −0.82 and a transition happening at zt = 1.36. We also discuss the importance of using the prior on M for constraining this model.