The H0 tension and non-minimal couplings to gravity

Theoretical models that aim to solve the tension between local measurements of the Hubble constant H0 and its inference from CMB data  have to include a modification to the standard LCDM model around the time of matter-radiation equality. I propose that such an early-time modification consists in a scalar field non-minimally coupled to the Ricci scalar, which behaves effectively like a dark radiation component and induces a time evolution of the Newton constant G. I present the cosmological dynamics for different functional forms of the coupling and show that some of them can simultaneously ease the H0 tension and be consistent with Solar System experiment that constrain deviations from General Relativity without the need of fine tuning. I compare these models with other attempts to solve the H0 tension and discuss phenomenological signatures that can be used to further test them.