As a test of general relativity on cosmological scales, we measure the γ parameter for the growth rate of density perturbations using the redshift-space distortion of the luminous red galaxies in the Sloan Digital Sky Survey (SDSS). Assuming the cosmological constant model, which matches the results of the WMAP experiment, we find γ = 0.62 + 1.8(σ8 − 0.8) ± 0.11 at 1-sigma confidence level, which is consistent with the prediction of general relativity, γ ≃ 0.55 ∼ 0.56. Rather high value of σ8 (≥ 0.87) is required to be consistent with the prediction of the cosmological DGP model, γ ≃ 0.68.
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Yamamoto et al. (2008) studied this question.