f(R) Gravity and its Cosmological Implications

TL;DR

This paper analyzes how viable $f(R)$ gravity models influence cosmic evolution and structure formation, revealing phantom crossing behavior and complex perturbation growth that align with observational data and neutrino mass constraints.

Contribution

It provides analytical and numerical insights into the evolution of $f(R)$ models, highlighting their unique perturbation growth and potential to explain observational phenomena.

Findings

Viable $f(R)$ models exhibit recent crossing of the phantom boundary.

The growth index of perturbations depends on time and wavenumber.

Anomalous growth can explain matter power spectrum features and neutrino mass effects.

Abstract

We have investigated the evolution of a homogeneous isotropic background of the Universe and inhomogeneous subhorizon matter density perturbations in viable $f(R)$ models of present dark energy and cosmic acceleration analytically and numerically. It is found that viable $f(R)$ models generically exhibit recent crossing of the phantom boundary $w_{\rm DE}=-1$. Furthermore, it is shown that the growth index of perturbations depends both on time and wavenumber. This anomalous growth may explain properties of the observational matter power spectrum from the SDSS data and can also partially counteract the spectrum suppression by massive neutrinos making larger values of the total sum of neutrino rest masses possible.