Some Cosmological Models of Early and Late Universe

Abstract

We study the effects of introducing modifications to General Relativity (GR) at newlinelarge scales as an alternative to exotic forms of matter required to respond the observed newlinecosmic acceleration. We survey the effects on cosmological tests of f(R,T) newlinegravity, C-field theory, Brans-Dicke theory, Lyra Geometry, Variable Equation of newlineState (EoS), Holographic Dark Energy. We find that, in addition to the changes newlineto the background expansion history of the Universe, these modifications have newlinesubstantial impact on structure formation and its observable predictions. newlineIn the construction of a cosmological model, the assumption of homogeneity newlineand isotropy of the Universe are motivated by the cosmological principle and newlinemathematical tractability of the resulting FRW models. So these symmetries can newlineonly be approximate. There are theoretical arguments and recent experimental newlinedata regarding cosmic background radiation anisotropies which support the existence newlineof an anisotropic phase that approaches an isotropic one. These observations newlineled us to consider more general anisotropic cosmologies, while retaining the assumption newlineof large scale spatial homogeneity. Wainright and Ellis (1997) have newlinediscussed the spatially homogeneous and anisotropic cosmological models which newlineprovide a richer structure, both geometrically and physically, than the FRWmodel newlineand play a significant role in the description of early Universe. newline