Growth Index of DGP Model and Current Growth Rate Data

TL;DR

This paper examines the growth index of the DGP modified gravity model across different curvature parameters and compares it with current growth rate data, finding consistency but emphasizing the need for more precise data to differentiate models.

Contribution

It extends the analysis of the growth index to the general DGP model with arbitrary curvature and tests its consistency with current observational data.

Findings

DGP model remains consistent with current growth rate data

More precise data needed to distinguish dark energy from modified gravity

Growth index analysis applicable to models with any curvature

Abstract

Recently, some efforts focus on differentiating dark energy and modified gravity with the growth function $\delta(z)$. In the literature, it is useful to parameterize the growth rate $f\equiv d\ln\delta/d\ln a=\Omega_m^\gamma$ with the growth index $\gamma$. In this note, we consider the general DGP model with any $\Omega_k$. We confront the growth index of DGP model with currently available growth rate data and find that the DGP model is still consistent with it. This implies that more and better growth rate data are required to distinguish between dark energy and modified gravity.