Probing Early Modification of Gravity with Planck, ACT and SPT

TL;DR

This study investigates an early modified gravity model with a scalar field non-minimally coupled to gravity, showing a preference for its contribution in recent CMB data and alleviating the Hubble tension.

Contribution

First analysis of the EMG model with latest ACT, SPT, and Planck data demonstrating a significant preference for non-zero EMG contribution and its impact on Hubble tension.

Findings

Preference for EMG contribution at >2σ with ACT DR4 data

NMC influences density perturbation evolution favorably

EMG model reduces H0 tension from 6σ to 3σ, and above 5σ with SH0ES data

Abstract

We consider a model of early modified gravity (EMG) that was recently proposed as a candidate to resolve the Hubble tension. The model consists in a scalar field $\sigma$ with a non-minimal coupling (NMC) to the Ricci curvature of the form $F(\sigma) = M_{\mathrm{pl}}^2+\xi\sigma^2$ and an effective mass induced by a quartic potential $V(\sigma) = \lambda \sigma^4/4$. We present the first analyses of the EMG model in light of the latest ACT DR4 and SPT-3G data in combination with full Planck data, and find a $\gtrsim 2\sigma$ preference for a non-zero EMG contribution from a combination of primary CMB data alone, mostly driven by ACT DR4 data. This is different from popular 'Early Dark Energy' models, which are detected only when the high-$\ell$ information from Planck temperature is removed. We find that the NMC plays a key role in controlling the evolution of density perturbations that is favored by the data over the minimally coupled case. Including measurements of supernovae luminosity distance from Pantheon+, baryonic acoustic oscillations and growth factor from BOSS, and CMB lensing of Planck leaves the preference unaffected. In the EMG model, the tension with S$H_0$ES is alleviated from $\sim 6\sigma$ to $\sim 3\sigma$. Further adding S$H_0$ES data rise the detection of the EMG model above $5\sigma$.