Big-bang nucleosynthesis and cosmic microwave background constraints on non-minimally coupled theories of gravity

TL;DR

This paper investigates how non-minimally coupled gravity theories affect baryon-to-photon ratio evolution, using big-bang nucleosynthesis and CMB data to constrain such models and rule out certain dark matter alternatives.

Contribution

It derives new constraints on non-minimally coupled gravity theories from cosmological data, showing some models are incompatible with observations.

Findings

Non-minimal coupling causes baryon-to-photon ratio non-conservation before decoupling.

Constraints from BBN and CMB limit the parameter space of these gravity models.

Some models previously considered as dark matter substitutes are ruled out.

Abstract

In this paper we show that the baryon-to-photon ratio $\eta$ is in general not conserved before decoupling in non-minimally coupled theories of gravity. We use big-bang nucleosynthesis and cosmic microwave background limits on the baryon-to-photon ratio $\eta$ to derive new constraints on modified gravity theories with a universal non-minimal coupling between matter and curvature, showing that they rule out a specific class of models previously considered in the literature as a substitute for the dark matter. We also compare these new constraints with the ones obtained from the COBE-FIRAS limits on CMB spectral distortions, highlighting the complementarity between them.