Scalar field cosmological models

Abstract

Observations of the cosmic microwave background and high red shift supernovae strongly suggest that our universe is spatially flat with about two thirds of its content made up of a yet unknown form of negative pressure matter called dark energy which is responsible for its late-time accelerated expansion. In the general theory of relativity (GR) the Friedmann-Lemaitre-Robertson-Walker (FLRW) solution with a cosmological constant A, known as the ACDM model, is the simplest model that agrees with current cosmological observations, and which associates the small positive cosmological constant with the source of dark energy. However the difficulty to explain the unrealistically small magnitude of A, i.e., the well known cosmological constant problem, has lead to an increased interest in the study of cosmology in alternative gravity theories, such as the scalar tensor theory of gravitation, where the presence of a non minimally coupled scalar field accounts for the observed acceleration. This project starts with a review of the general scalar tensor theory of gravity and discusses a number of homogeneous and isotropic scalar-tensor cosmological models in the literature. Starting with the FLRW metric (with and without curvature) and using a minimally, non minimally or conformally coupled scalar field in the Lagrangian, we examine the possibility of obtaining a new isotropic and homogeneous scalar-tensor model, whose large scale geometry is similar to that of the standard ACDM model in GR. The effect of the scalar field on the evolution of the universe and its late time acceleration is investigated.