Two-fluid atmosphere from decelerating to accelerating FRW dark energy models

The evolution of the dark energy parameter within the scope of a spatially homogeneous and isotropic Friedmann-Robertson-Walker (FRW) model filled with perfect fluid and dark energy components is studied by generalizing the recent results (Amirhashchi et al. in Int. J. Theor. Phys. 50: 3529, 2011b). The two sources are claimed to interact minimally so that their energy momentum tensors are conserved separately. The conception of time-dependent deceleration parameter (DP) with some suitable assumption yields an average scale factor $a = [\sinh (αt)]^{\frac{1}{n}}$, with $α$ and $n$ being positive arbitrary constants. For $0 < n \leq 1$, this generates a class of accelerating models while for $n > 1$, the models of universe exhibit phase transition from early decelerating phase to present accelerating phase which is supported with the results from recent astrophysical observations. It is observed that the transition red shift ($z_{t}$) for our derived model with $q_{0} = -0.73$ is $\cong 0.32$. This is in good agreement with the cosmological observations in the literature. Some physical and geometric properties of the model along with physical acceptability of cosmological solutions have been discussed in detail.

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