The present universe in the Einstein frame, metric-affine R+1/R gravity

TL;DR

This paper investigates the current universe using metric-affine R+1/R gravity in the Einstein frame, revealing deviations in matter density scaling and consistency with some observational parameters, but differences in transition redshift.

Contribution

It applies the Palatini variational principle to R+1/R gravity in the Einstein frame, analyzing its implications for current cosmological parameters and universe evolution.

Findings

Deviations in matter density scaling in the present epoch.

Current deceleration parameter aligns with observations.

Transition redshift matches DM but exceeds SNIa estimates.

Abstract

We study the present, flat isotropic universe in 1/R-modified gravity. We use the Palatini (metric-affine) variational principle and the Einstein (metric-compatible connected) conformal frame. We show that the energy density scaling deviates from the usual scaling for nonrelativistic matter, and the largest deviation occurs in the present epoch. We find that the current deceleration parameter derived from the apparent matter density parameter is consistent with observations. There is also a small overlap between the predicted and observed values for the redshift derivative of the deceleration parameter. The predicted redshift of the deceleration-to-acceleration transition agrees with that in the \Lambda-CDM model but it is larger than the value estimated from SNIa observations.