A larger value for $H_0$ by an evolving gravitational constant
  We provide further evidence that a massless cosmological scalar field with a
non-minimal coupling to the Ricci curvature of the type $M^2_{\rm pl}(1+\xi
\sigma^n/M_{\rm pl}^n) $ alleviates the existing tension between local
measurements of the Hubble constant and its inference from CMB anisotropies and
baryonic acoustic oscillations data in presence of a cosmological constant. In
these models, the expansion history is modified compared to $\Lambda$CDM at
early time, mimicking a change in the effective number of relativistic species,
and gravity weakens after matter-radiation equality. Compared to $\Lambda$CDM,
a quadratic ($n=2$) coupling increases the Hubble constant when {\em Planck}
2018 (alone or in combination with BAO and SH0ES) measurements data are used in
the analysis. Negative values of the coupling, for which the scalar field
decreases, seem favored and consistency with Solar System can be naturally
achieved for a large portion of the parameter space without the need of any
screening mechanism. We show that our results are robust to the choice of $n$,
also presenting the analysis for $n=4$.
