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 gamma as a function of redshift. At the linear approximation: gamma(z) approximate to gamma(0) + gamma(0)'z, we find that, for 0.2 <= Omega m.0 <= 0.35, gamma(0) takes the value from 0.658 to 0.671, and gamma(0)' ranges from 0.035 to 0.042. With three low redshift observational data of the growth factor, we obtain the observational constraints on gamma(0) and gamma(0)' for the ACDM and DGP models and find that the observations favor the ACDM model but at the I a confidence level both the ACDM and DGP models are consistent with the observations. (C) 2009 Elsevier B.V. All rights reserved.