Phantom-Like Behavior in $f(R)$-Gravity

TL;DR

This paper explores how certain $f(R)$-gravity models can mimic phantom-like cosmic behavior without involving problematic phantom fields, by choosing specific functional forms of $f(R)$ that satisfy energy conditions.

Contribution

It demonstrates that $f(R)$-gravity can produce phantom-like effects without instabilities, depending on the chosen functional form of $f(R)$ and its parameters.

Findings

Phantom-like behavior can be realized in $f(R)$-gravity models.

Null energy condition can be satisfied in certain parameter subspaces.

No need for phantom fields that cause instabilities.

Abstract

We investigate possible realization of the phantom-like behavior in the framework of $f(R)$-gravity models where there are no phantom fields in the matter sector of the theory. By adopting some observationally reliable ansatz for $f(R)$, we show that it is possible to realize phantom-like behavior in $f(R)$-gravity without introduction of phantom fields that suffer from instabilities and violation of the null energy condition. Depending on the choice of $f(R)$, the null energy condition is fulfilled in some subspaces of each model parameter space.