DR. MD. WALI HOSSAIN

Apart from cosmological constant scalar field or modification of gravity can give rise to late time acceleration. Scalar field or modification of gravity can give dynamical dark energy where the energy density of the component, responsible for late time acceleration, varies with time. For scalar field we can have tracker or thawing behavior. For tracker behavior scalar field tracks the background in the past and takes over the background in the recent past giving rise to late time acceleration. In the thawing behavior scalar field behaves like a cosmological constant for the maximum time of the evolution of the Universe in the past and starts evolving from the recent past. Dynamics of scalar field depends on the nature of the potential. Thawing class of models can be achieved for many scalar field potential but there are few potentials which can give rise to tracker behavior. The speaker will describe the dynamics of the scalar field in the cosmological background and as a particular model he will consider cubic Galileon model with potential where apart from the background evolution he will also talk about the cosmological perturbation. Galileon theory preserves galilean shift symmetry but cubic galileon without potential term can not give rise to late time acceleration. Adding a potential term in the cubic Galileon breaks the shift symmetry but it gives late time acceleration. We will consider a scenario where there is a nonminimal coupling between scalar field and matter. In this kind of scenarios Newton’s constant varies with time. In the scenario under consideration effective Newton’s constant is same as the Newton’s constant G at the high redshifts but deviates from G at the lower redshifts.