Phenomenological Gravitational Phase Transition: Early and Late Modifications

TL;DR

This paper explores a generalized gravitational phase transition model aiming to resolve the Hubble tension, but finds it incompatible with BAO data, thus limiting its effectiveness as a solution.

Contribution

It extends the gravitational phase transition concept to early universe modifications and tests its viability against BAO data, revealing significant limitations.

Findings

BAO data favors the standard $\\Lambda$CDM model with low Hubble constant

Generalized GPT cannot reconcile high local H_0 with BAO constraints

The model's parameter space is too constrained to solve the Hubble tension

Abstract

In this work we generalize the idea of a gravitational phase transition or GPT at late times to allow for a modified gravity scenario in the early universe as well. The original GPT was shown to simultaneously relax the $H_0$ and $\sigma_8$ tensions and {\it Planck} internal inconsistencies. However, the primary results from GPT predictions implied disagreement with the data from the baryonic acoustic oscillations (BAO). Here we investigate whether the generalized GPT scenario could address the Hubble tension in the presence of the BAO data as well. We find that, despite the vastly enlarged gravitational parameter space, the BAO data strongly prefer the $\Lambda$CDM paradigm with a low inferred Hubble constant, $68.03\pm 0.76 $ km/s/Mpc, in tension with the local $H_0$ measurements from Riess et al., $H_0=74.03\pm 1.42$ km/s/Mpc. This failure of the generalized GPT scenario to host the P18-BAO-R19 trio is of significance and noticeably shrinks the space of possible gravitational solutions to the Hubble tension.