Emergence of dynamical dark energy from polynomial $f(R)$ theory in Palatini formalism

TL;DR

This paper explores how polynomial $f(R)$ gravity in the Palatini formalism can naturally produce emergent dark energy, analyzing the cosmological dynamics, singularities, and potential advantages of the Einstein frame reformulation.

Contribution

It introduces a polynomial $f(R)$ model in Palatini formalism, showing how it leads to emergent dark energy and resolves some singularities through Einstein frame analysis.

Findings

Emergent dark energy arises from polynomial $f(R)$ modifications.

Some singularities are resolved in the Einstein frame.

The model simplifies to a scalar field with a potential governing dark energy.

Abstract

We consider FRW cosmology in $f(R)= R+ \gamma R^2+\delta R^3$ modified framework. The Palatini approach reduces its dynamics to the simple generalization of Friedmann equation. Thus we study the dynamics in two-dimensional phase space with some details. After reformulation of the model in the Einstein frame, it reduces to the FRW cosmological model with a homogeneous scalar field and vanishing kinetic energy term. This potential determines the running cosmological constant term as a function of the Ricci scalar. As a result we obtain the emergent dark energy parametrization from the covariant theory. We study also singularities of the model and demonstrate that in the Einstein frame some undesirable singularities disappear.