Cosmic acceleration from modified gravity with Palatini formalism

TL;DR

This paper explores modified gravity models with a scalar field in Palatini formalism, analyzing their cosmological dynamics, fitting them to astrophysical data, and comparing their predictions to the standard LCDM model.

Contribution

It introduces a new class of FRW cosmological models with a scalar field non-minimally coupled to curvature in Palatini formalism, including a quadratic term, and assesses their viability against observational data.

Findings

Models fit current astrophysical data well.

Presence of a final sudden singularity in the models.

CMB data favors the standard LCDM model over these alternatives.

Abstract

We study new FRW type cosmological models of modified gravity treated on the background of Palatini approach. These models are generalization of Einstein gravity by the presence of a scalar field non-minimally coupled to the curvature. The models employ Starobinsky's term in the Lagrangian and dust matter. Therefore, as a by-product, an exhausted cosmological analysis of general relativity amended by quadratic term is presented. We investigate dynamics of our models, confront them with the currently available astrophysical data as well as against LCDM model. We have used the dynamical system methods in order to investigate dynamics of the models. It reveals the presence of a final sudden singularity. Fitting free parameters we have demonstrated by statistical analysis that this class of models is in a very good agreement with the data (including CMB measurements) as well as with the standard LCDM model predictions. One has to use statefinder diagnostic in order to discriminate among them. Therefore Bayesian methods of model selection have been employed in order to indicate preferred model. Only in the light of CMB data the concordance model remains invincible.