Growth factor parametrization and modified gravity

TL;DR

This paper investigates how the growth index parameter varies with matter density and uses observational data to test different cosmological models, providing constraints on parameters and disfavoring some modified gravity theories.

Contribution

It introduces a refined parametrization of the growth index considering its dependence on matter density and applies observational data to constrain cosmological models.

Findings

The data strongly disfavor the Dvali-Gabadadze-Porrati model.

For dark energy with constant equation of state, Ω₀=0.27±0.02, w=-0.97±0.09.

For ΛCDM, γ=0.64^{+0.17}_{-0.15}. The GGP model yields γ=0.55^{+0.14}_{-0.13}.

Abstract

The growth rate of matter perturbation and the expansion rate of the Universe can be used to distinguish modified gravity and dark energy models in explaining the cosmic acceleration. The growth rate is parametrized by the growth index $\gamma$. We discuss the dependence of $\gamma$ on the matter energy density $\Omega$ and its current value $\Omega_0$ for a more accurate approximation of the growth factor. The observational data, including the data of the growth rate, are used to fit different models. The data strongly disfavor the Dvali-Gabadadze-Porrati model. For the dark energy model with a constant equation of state, we find that $\Omega_0=0.27\pm 0.02$ and $w=-0.97\pm 0.09$. For the $\Lambda$CDM model, we find that $\gamma=0.64^{+0.17}_{-0.15}$. For the Dvali-Gabadadze-Porrati model, we find that $\gamma=0.55^{+0.14}_{-0.13}$.