Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The growth index of matter perturbations and modified gravity   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
{\em 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.

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The categories of this paper are: cmp-lg
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The categories of this paper are: hep-th
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The categories of this paper are: quant-ph
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The categories of this paper are: math-ph
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The categories of this paper are: nlin
15
The categories of this paper are: nucl-ex
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The categories of this paper are: dg-ga
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The categories of this paper are: chem-ph
4
The categories of this paper are: cond-mat
12
The categories of this paper are: nucl-th
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The categories of this paper are: bayes-an
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The categories of this paper are: physics
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The categories of this paper are: q-bio
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The categories of this paper are: patt-sol
2
The categories of this paper are: math
11
The categories of this paper are: hep-lat