Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2012-03-30
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
7 pages, 4 figures submitted to MNRAS on 27/03/2012. We use growth data from Song & Percival (2009), Blake et al. (2011) and S
Scientific paper
We place tight constraints on the growth index $\gamma$ by using the recent growth history results of 2dFGRS, SDSS-LRG, VIMOS-VLT deep Survey (VVDS) and WiggleZ datasets. In particular, we investigate several parametrizations of the growth index $\gamma(z)$, by comparing their cosmological evolution using observational growth rate data at different redshifts. Utilizing a standard likelihood analysis we find that the use of the combined growth data provided by the 2dFGRS, SDSS-LRG, VVDS and {\em WiggleZ} galaxy surveys, puts the most stringent constraints on the value of the growth index. As an example, assuming a constant growth index we obtain that $\gamma=0.602\pm 0.055$ for the concordance $\Lambda$CDM expansion model. Concerning the Dvali-Gabadadze-Porrati gravity model, we find $\gamma=0.503\pm 0.06$ which is lower, and almost $3\sigma$ away, from the theoretically predicted value of $\gamma_{DGP}\simeq 11/16$. Finally, based on a time varying growth index we also confirm that the combined growth data disfavor the DGP gravity.
Basilakos Spyros
Pouri Athina
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