About matter and dark-energy domination eras in R^n gravity or lack thereof

TL;DR

This paper investigates R^n gravity models and finds they can produce either late-time acceleration or matter domination, but not both simultaneously, suggesting these models are inconsistent with observations as alternatives to dark energy.

Contribution

The study provides numerical evidence that R^n gravity models cannot simultaneously produce matter domination and late-time acceleration without relying on scalar-tensor mappings.

Findings

R^n models produce either acceleration or matter domination, not both

Results confirm previous findings using a different, frame-independent approach

R^n models are likely incompatible with observational data

Abstract

We provide further numerical evidence which shows that R^n models in f(R) metric gravity whether produces a late time acceleration in the Universe or a matter domination era (usually a transient one) but not both. Our results confirm the findings of Amendola et al. (2007), but using a different approach that avoids the mapping to scalar-tensor theories of gravity, and therefore, dispense us from any discussion or debate about frames (Einstein vs Jordan) which are endemic in this subject. This class of models has been used extensively in the literature as an alternative to the dark energy, but should be considered ruled out for being inconsistent with observations. Finally, we discuss a caveat in the analysis by Faraoni (2011), which was used to further constrain these models by using a chameleon mechanism.