Brans-Dicke gravity with a cosmological constant smoothes out $Λ$CDM tensions

Abstract: We analyze Brans-Dicke gravity with a cosmological constant, $\Lambda$, and cold dark matter (BD-$\Lambda$CDM for short) in the light of the latest cosmological observations on distant supernovae, Hubble rate measurements at different redshifts, baryonic acoustic oscillations, large scale structure formation data, gravitational weak-lensing and the cosmic microwave background under full Planck 2015 CMB likelihood. Our analysis includes both the background and perturbations equations. We find that BD-$\Lambda$CDM is observationally favored as compared to the concordance $\Lambda$CDM model, which is traditionally defined within General Relativity (GR). In particular, some well-known persisting tensions of the $\Lambda$CDM with the data, such as the excess in the mass fluctuation amplitude $\sigma_8$ and specially the acute $H_0$-tension with the local measurements, essentially disappear in this context. Furthermore, viewed from the GR standpoint, BD-$\Lambda$CDM cosmology mimics quintessence at $\gtrsim3\sigma$ c.l. near our time.