SOME INFLATIONARY AND COSMIC ISSUES IN GENERAL RELATIVITY

Abstract

In this thesis, we investigate two interesting issues. First, we study the validity of gen- eralized second law of thermodynamics for FRW universe bounded by four horizons, i.e., Hubble, apparent, particle and event horizons in the framework of non-linear electrodynamics. We assume that the universe is composed of dark matter, magnetic ¯eld and some unknown component of dark energy with two di®erent interacting terms. It is found that energy transfer from dark energy to magnetic energy depends upon the sign of interacting terms. In this scenario, we calculate energy densities of dark matter and other dark energy °uid. It turns out that this law always holds on the Hubble and apparent horizons, but fails on the particle and event horizons for both interacting and non-interacting cases. Second, we study warm in°ation using vector ¯elds in the background of locally rotationally symmetric Bianchi I universe model. To discuss in°ation, we formulate the ¯eld equations, slow-roll and perturbation parameters (scalar and tensor power spectra, their spectral indices and tensor-scalar ratio) under slow-roll approximation. These parameters are evaluated in terms of in°aton during intermediate and logame- diate in°ationary regimes by taking variable and constant dissipation coe±cient. The graphical analysis of these parameters is shown to check compatibility of the model with WMAP7 and Planck observational data. We also deal with the dynamics of warm in°ation in which slow-roll in°ation is driven by non-Abelian gauge ¯elds in the same background metric. In this context, the solutions of in°aton and in°ationary parameters during intermediate as well as xiv xv logamediate in°ationary eras are evaluated. It is concluded that anisotropic in°ation- ary universe model with non-Abelian gauge ¯elds remain compatible with WMAP7 data. We then assume that the anisotropic universe is composed of in°aton and im- perfect °uid having radiation and bulk viscous pressure. The analysis is made by taking dissipation and bulk viscous coe±cients to be variable as well as constant. We constrain the model as well as cosmological parameters using recent Planck and WMAP7 probe. Finally, we consider an in°ationary FRW universe model in the context of gen- eralized cosmic Chaplygin gas by taking matter ¯eld as standard and tachyon scalar ¯elds. The solution of in°aton ¯elds and scalar potentials during intermediate and logamediate in°ationary regimes are found by modifying the ¯rst Friedmann equa- tion. The graphical behavior of observed physical parameter shows that the model remains incompatible with WMAP7 and Planck observational data in each case. We also study the e®ects of bulk viscous pressure on this model assuming in°aton and imperfect °uid as constituents of the universe. We evaluate in°aton ¯elds, poten- tials and entropy density for variable as well as constant dissipation and bulk viscous coe±cients in weak and strong dissipated regimes during intermediate era. The cor- responding parameters are constrained using recent Planck, WMAP7 and BICEP2 probes.