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- This paper examines the stability of the transition from the early decelerating stage of the Universe to the recent accelerating stage for the perfect fluid cosmological locally rotationally symmetric (LRS) Bianchi-I model in š(š ,š) theory. To determine the solution of field equations, the idea of a time varying deceleration parameter (DP) which yields a scale factor, for which the Universe attains a phase transition scenario and is consistent with recent cosmological observations, is used. The time-dependent h DP yields a scale factor a = exp ā 1 Ī² 2Ī²t +k i , where Ī² and k are respectively arbitrary and integration constants. By using the recent constraints (H0 = 73.8, and q0 = ā0.54) from Type Ia Supernova (SN Ia) data in combination with Baryonic Acoustic Oscillations (BAO) and Cosmic Microwave Background (CMB) observations (Giostri et al.), we obtain the values of Ī² = 0.0062 and k = 0.000016 for which we have derived a cosmological model from the early decelerated phase to the present accelerating phase. By applying other recent constraints (H0 = 73.8, q0 = ā0.73) from SNe Ia Union data (Cunha), we obtain the values of Ī² = 0.0036 and k = 0.000084 for which we have derived a cosmological model in the accelerating phase only. We have compared both models with experimental data. The stability of the background solution has been examined also for the metric perturbations alongside the properties of future singularities in a Universe ruled by dark energy with phantom type fluid. We demonstrate the presence of a stable fixed point with a condition of state Ļ < ā1 and numerically affirm this is really a late-time attractor in the ghost overwhelmed Universe. Some physical and geometric properties of the model are found and examined.
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- This paper examines the physical behaviour of the transition of the LRS Bianchi type-I perfect fluid cosmological models from early decelerating to the current accelerating phase within the framework of the š(š ,š) theory of gravity. To determine the solution of the field equations, the concept of a time dependent deceleration parameter is used. This yields scale factors for which the universe attains a phase transition scenario, and is consistent with recent cosmological observations. Two cases are considered, firstly a(t) = sinh1/n(Ī±t), where n and Ī± are positive constants. For 0 1, the universe attains a phase transition from an early decelerating to the present accelerating phase. This model 1 starts from quintessence (Ļ>ā1) initially and ended up with phantom phase (Ļ<ā1) when t āā. The second case is a(t) = (tket)1/n, where n and k are positive constants. It is observed that for n ā„ 2andk = 1, a class of transit models of the universe are obtained. The model 2 belongs to the scenario of phantom energy (Ļ<ā1). We have observed the existence of type-III singularity in our model 2. Some physical and geometric properties of the models are found and discussed.
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