The growth of linear perturbations in the DGP model

We study the linear growth of matter perturbations in the DGP model with the growth index γ as a function of redshift. At the linear approximation: γ(z)≈γ0+γ0′z, we find that, for 0.2⩽Ωm,0⩽0.35, γ0 takes the value from 0.658 to 0.671, and γ0′ ranges from 0.035 to 0.042. With three low redshift observational data of the growth factor, we obtain the observational constraints on γ0 and γ0′ for the ΛCDM and DGP models and find that the observations favor the ΛCDM model but at the 1σ confidence level both the ΛCDM and DGP models are consistent with the observations.