The $\Lambda$CDM growth rate of structure revisited
  We re-examine the growth index of the concordance $\Lambda$ cosmology in the
light of the latest 6dF and {\em WiggleZ} data. In particular, we investigate
five different models for the growth index $\gamma$, by comparing their
cosmological evolution using observational data of the growth rate of structure
formation at different redshifts. Performing a joint likelihood analysis of the
recent supernovae type Ia data, the Cosmic Microwave Background shift
parameter, Baryonic Acoustic Oscillations and the growth rate data, we
determine the free parameters of the $\gamma(z)$ parametrizations and we
statistically quantify their ability to represent the observations. We find
that the addition of the 6dF and {\em WiggleZ} growth data in the likelihood
analysis improves significantly the statistical results. As an example,
considering a constant growth index we find $\Omega_{m0}=0.273\pm 0.011$ and
$\gamma=0.586^{+0.079}_{-0.074}$.
