GCG Parametrization for Growth Function and Current Constraints
  We study the linear growth function $f$ for large scale structures in a
cosmological scenario where Generalised Chaplygin Gas (GCG) serves as dark
energy candidate. We parametrize the growth index parameter as a function of
redshift and do a comparative study between the theoretical growth rate and the
proposed parametrization. Moreover, we demonstrate that growth rates for a wide
range of dark energy models can be modeled accurately by our proposed
parametrization. Finally, we compile a data set consisting of 28 data points
within redshift range (0.15,3.8) to constrain the growth rate. It includes
direct growth data from various projects/surveys including the latest data from
the Wiggle-Z measurements. It also includes data constraining growth indirectly
through the rms mass fluctuation $\sigma_8(z)$ inferred from Ly-$\alpha$
measurements at various redshifts. By fitting our proposed parametrization for
$f$ to these data, we show that growth history of large scale structures of the
universe although allows a transient acceleration, one cannot distinguish it at
present with an eternally accelerating universe.
