Bridge the Cosmological Tensions with Thawing Gravity

TL;DR

Thawing Gravity, a non-minimally coupled scalar-tensor theory, better explains cosmological tensions like H0 and S8 compared to ΛCDM, fitting observations and predicting a varying Newtonian constant.

Contribution

The paper introduces Thawing Gravity as a novel scalar-tensor model that alleviates cosmological tensions and provides a better fit to observational data than ΛCDM.

Findings

Thawing Gravity has moderate to very strong Bayesian evidence over ΛCDM.

It predicts a higher early-universe Newtonian constant G_CMB, hinting at a variation from G_N.

The model yields H0 and S8 values consistent with local and large-scale structure measurements.

Abstract

It is found that a non-minimally coupled scalar tensor theory, Thawing Gravity (TG), can explain multiple tensions plaguing the standard cosmological model $\Lambda$CDM while fitting better to observations than the latter. Using the standard Bayes model comparison method, TG has moderate evidence over $\Lambda$CDM with a Bayes factor $\ln B=+1.5$ in the baseline analysis including CMB, BAO and SNIa. In the baseline+$H_0$ analysis which further takes into account the Cepheids calibration of the SNIa distance ladder from SH0ES, TG has very strong evidence over $\Lambda$CDM with $\ln B=+11.8$. In particular, TG yields $H_0=71.78\pm0.86 \ {\rm km/s/Mpc}$ and $S_8=0.793\pm0.012$, consistent with both the local $H_0$ measurement and the large scale structure surveys. TG predicts a prerecombination Newtonian constant $G_{\rm CMB}$ different from today's value $G_N$. A $\sim2\sigma$ hint for $G_{\rm CMB}/G_N>1$ is recovered in the baseline analysis with CMB+BAO+SNIa, which becomes a $>4\sigma$ detection when one further takes into account the local $H_0$ measurement. The obtained $G_{\rm CMB}/G_N$ is consistent with current BBN constraint and can be tested by future observations.