$H_0$ tension as a hint for a transition in gravitational theory

TL;DR

This paper introduces "uΛCDM, a new cosmological model based on uber-gravity, which features a transition in gravitational behavior that can marginally alleviate the H0 tension using observational data.

Contribution

The paper proposes a novel "uΛCDM model based on uber-gravity with a phase transition, offering a potential solution to the H0 tension and exploring its observational implications.

Findings

"uΛCDM marginally improves H0 tension fit.

The model fits BAO, SNe, and CMB data with specific parameters.

Potential observable signatures in large-scale structure at z < z_⊕.

Abstract

We propose a cosmological model, \"u$\Lambda$CDM, based on {\it \"uber-gravity}, which is a canonical ensemble average of many theories of gravity. In this model, we have a sharp transition from (a purely) $\Lambda$CDM era to a phase in which the Ricci scalar is a constant. This transition occurs when the Ricci scalar reaches a critical scale or alternatively at a transition redshift, $z_\oplus$. We use the observations of baryonic acoustic oscillations (BAO) and Supernovae Ia (SNe), as well as the cosmic microwave background (CMB) data to constrain \"u$\Lambda$CDM. This yields $H_0=70.6_{-1.3}^{+1.1}$ km/s/Mpc, $\Omega_m=0.2861 \pm{0.0092} $ and $z_\oplus=0.537_{-0.375}^{+0.277}$, providing a marginally better fit with a Akaike information criterion of 0.8. %After adding in the data from BAO in the Lyman-$\alpha$ forest in quasar spectra, we get $\Delta\chi^2=-2.14$, where the best fit occurs at $H_0=71.2_{-1.5}^{+1.8}$ km/s/Mpc, $\Omega_m=0.280\pm 0.013$ and $z_{\oplus}= 0.41^{+0.31}_{-0.29}$. Therefore, \"u$\Lambda$CDM can ease the $H_0$-tension, albeit marginally, with one additional free parameter. We also provide a preliminary study of the linear perturbation theory in \"u$\Lambda$CDM which points to interesting potential {\it smoking guns} in the observations of large scales structure at $z < z_{\oplus}$.