Alleviating the H0 tension with new gravitational scalar tensor theories

We investigate the cosmological applications of new gravitational scalar-tensor theories, and we analyze them in the light of H0 tension. In these theories, the Lagrangian contains the Ricci scalar and its first and second derivatives in a specific combination that makes them free of ghosts, thus corresponding to healthy biscalar extensions of general relativity. We examine two specific models, and for particular choices of the model parameters, we find that the effect of the additional terms is negligible at high redshifts, obtaining a coincidence with ΛCDM cosmology; however, as time passes, the deviation increases, and thus, at low redshifts the Hubble parameter acquires increased values (H0≈74 km/s/Mpc) in a controlled way. The mechanism behind this behavior is the fact that the effective dark-energy equation-of-state parameter exhibits phantom behavior, which implies faster expansion, which is one of the sufficient conditions that are capable of alleviating the H0 tension. Lastly, we confront the models with cosmic chronometer (CC) data, showing full agreement within 1σ confidence level.