Scalar-Tensor Gravity and DESI 2024 BAO data

Abstract

We discuss the implications of the DESI 2024 BAO data on scalar-tensor models of gravity. We consider four representative models: induced gravity (IG, equivalent to Jordan-Brans-Dicke), where we either fix today's value of the effective gravitational constant on cosmological scales to the Newton's constant or allow them to differ, Jordan-Brans-Dicke supplemented with a Galileon term (BDG), and early modified gravity (EMG) with a conformal coupling. In this way it is possible to investigate how different modified gravity models compare with each other when confronted with DESI 2024 BAO data. Compared to previous analyses, for all of these models, the combination of Planck and DESI data favors a larger value of the key parameter of the theory, such as the nonminimal coupling to gravity or the Galileon term, leading also to a larger value of $H_0$, due to the known degeneracy between these parameters. These new results are mainly driven by the first two redshift bins of DESI. In BDG, in which we find the largest value for $H_0$ among the models considered, the combination of Planck and DESI is consistent with CCHP results and reduces the $H_0$ tension with the SH0ES measurement to $1.2\sigma$ (compared to $4.5\sigma$ of $\Lambda$CDM in our Planck + DESI analysis).