Accelerating Expansion of the Universe in Modified Symmetric Teleparallel Gravity

In the last century, theoretical and experimental developments have established the General Relativity theory as the most successful theory for describing the gravitational phenomenon. On the other hand, in the last two decades, multiple observational probes have strongly favored the discovery of the acceleration of cosmic expansion. The observational enhancement and development in precision cosmology indicate a requirement to go beyond General Relativity and to search for an alternate description that can resolve the persistent issues. In Chapter 1, we highlight some important elements of observational cosmology. In Chapters 2 and 3, we investigate the f(Q) gravity in the presence of viscosity in the cosmic fluid. In Chapters 4 and 5, we explore the constraints on the various classes of non-linear f(Q) gravity models in both coincident and non-coincident formalism, respectively. In Chapter 6, we present a covariant formulation and energy balance equation for the f(Q,T) gravity, which is an extension of f(Q) gravity. Finally, in Chapter 7, we briefly summarize the outcomes of the present thesis and the future scope.