Cosmological constraints on new scalar gravitational interactions

Scalar-Tensor theory is a framework for modified gravity that encompasses many well-studied alternatives to General Relativity. Of particular interests are theories which possess a screening mechanism, which allows for the satisfaction of the bounds of solar system and laboratory scale tests of gravity, while giving rise to novel effects on cosmological scales. Among these are Large-Curvature f(R) as well as Chameleon, Symmetron and Dilaton gravity. All of these models can be described in terms of a recently introduced parametrization of Scalar-Tensor Theory, which involves two free functions of time alone. These models have been implemented by modifying the existing code MGCAMB. In this thesis, we discuss our implementation of these models. We present the results of Fisher forecasts for the constraints on the parameters of the 4 aforementioned models, taking the Large Synoptic Survey Telescope (LSST) and Planck as representative surveys. We also use the Principal Components Analysis approach, forecasting constraints for bins of the two functions upon discretization