Palatini f(R) Cosmology

TL;DR

This paper explores Palatini f(R) gravity models by analyzing their impact on cosmic expansion, linear growth, and perturbation stability, providing insights into their viability as alternatives to dark energy.

Contribution

It offers a detailed comparison of cosmic evolution and perturbations in Palatini f(R) models, highlighting stability conditions and perturbation behavior across scales.

Findings

Superhorizon metric evolution stability varies by model

Matter density fluctuations follow specific differential equations

Cosmic expansion history differs from standard models

Abstract

We investigate the modified gravity theories in terms of the effective dark energy models. We compare the cosmic expansion history and the linear growth in different models. We also study the evolution of linear cosmological perturbations in modified theories of gravity assuming the Palatini formalism. We find the stability of the superhorizon metric evolution depends on models. We also study the matter density fluctuation in the general gauge and show the differential equations in super and sub-horizon scales.