Some bouncing models are investigated in the frame work of an extended theory of Gravity. The extended gravity model is a simple extension of the General Relativity where an additional matter geometry coupling is introduced to account for the late time cosmic speed up phenomena. The dynamics of the models are discussed in the background of a flat FRW universe. Some viable models are reconstructed for some assumed bouncing scale factors. The behavior of the models are found to be decided mostly by the parameters of the respective models.PACS number: 04.50kd.

We have investigated some cosmic transit models in the framework of an extended gravity theory where the usual Ricci scalar in the gravitational action is replaced by a sum of the Ricci scalar and a term proportional to the trace of the energy momentum tensor. A hybrid scale factor is assumed to simulate the cosmic transit behaviour. The hybrid scale factor has two parameters that describe the behaviour of the model at an initial epoch and at a late epoch. The parameters of the hybrid scale factor have been constrained from the cosmic transit behaviour. Four different cosmic transit models have been constructed and are confronted with the observational Hubble parameter data. A cosmographic test for the cosmic transit models is conducted to assess their dynamical evolution. The effect of the model parameters on the cosmic dynamics has been investigated.

We study effect of the cosmological constant on compact star with equation of state provided by quark-meson coupling (QMC) model. In this model, baryons are described as a system of nonoverlapping bags interacting through the scalar and vector mesons. We derive the Tolman–Oppenheimer–Volkoff (TOV) equation taking into account the cosmological constant in static and spherically symmetric metric. Using the equation of state given by QMC model, the mass–radius relationship of the compact star has been computed for various values of the cosmological constant.

The Cosmological principle is the hypothesis that the universe is spatially homogeneous and isotropic. In the study of cosmological model, the Einstein field equations and construct a static model of the universe. A method has proposed by Berman 1991 3 on the basis of the conservation law, to incorporate the variable Gravitational constant ' G ' and Cosmological constant '  ' in the Einstein field equations. The solutions are obtained by choosing suitable values for the constant  and  , a number of cosmological models may be constructed and the validity of these models may be tested on the theoretical and observational grounds.