Larger value for <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msub><mml:mi>H</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:math> by an evolving gravitational constant
Matteo Braglia, M. Ballardini, William T. Emond, F. Finelli⋆, A. Emir Gümrükçüoğlu, K. Koyama, D. Paoletti
Abstract
We provide further evidence that a massless cosmological scalar field with a nonminimal coupling to the Ricci curvature of the type ${M}_{\mathrm{pl}}^{2}(1+\ensuremath{\xi}{\ensuremath{\sigma}}^{n}/{M}_{\mathrm{pl}}^{n})$ alleviates the existing tension between local measurements of the Hubble constant and its inference from cosmic microwave background anisotropies and baryonic acoustic oscillations data in the presence of a cosmological constant. In these models, the expansion history is modified compared to $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ at early time, mimicking a change in the effective number of relativistic species, and gravity weakens after matter-radiation equality. Compared to $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$, a quadratic ($n=2$) coupling increases the Hubble constant when 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 the 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 $n=4$.