Strong Einstein-Hilbert Gravity Inflation and ACT Phenomenology

TL;DR

This paper investigates how rescaled scalar theories of gravity, which modify Einstein-Hilbert gravity at strong curvatures, can align with recent cosmological observations on primordial perturbations and gravitational waves.

Contribution

It introduces rescaled effective scalar theories of gravity and demonstrates their compatibility with ACT and Planck/BICEP observational constraints.

Findings

Stronger gravity theories with rescaling parameter α<1 fit observational data.

Rescaled scalar theories can emerge from effective $f(R,\, ext{phi})$ gravity at high curvature.

Canonical scalar fields with rescaled gravity are compatible with current cosmological constraints.

Abstract

In this work we study rescaled effective single scalar field theories, and we confront these with the ACT constraint on the spectral index of the scalar primordial perturbations and the updated BICEP/Planck constraint on the tensor-to-scalar ratio. Rescaled scalar theories of gravity may be the result of an effective $f(R,\phi)$ gravity at strong curvature regimes, which may result on a rescaling of the Einstein-Hilbert term of the form $\sim \alpha R$. It turns out that canonical scalar field theories with stronger gravity compared to standard Einstein-Hilbert gravity can be compatible with the ACT and updated Planck/BICEP constraints, with stronger gravity meaning that the rescaling parameter $\alpha$ takes values smaller than unity.