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Physics of Structure Formation in the Universe

In recent years, unprecedented progress in observational cosmology has revealed a great deal of information about the formation and evolution of structures in the universe. This, in turn, has raised many challenging issues for the theorists. In the thesis, we have addressed two such key issues, namely, (a) the formation of baryonic structures and (b) the nature of dark matter and dark energy and the limitations in determining their nature from observations. The main results from the thesis are: (i) The baryons in the intergalactic medium at redshifts z \sim 2.5 can be modelled (both analytically and semi-analytically) by accounting for the non-linearities in the density field through lognormal approximation. Our results agree with observations, and can be used for constraining parameters related to the baryons. (ii) A simple model based on baryon conservation, along with observational estimates of cosmic star formation rate, correctly predicts the abundance of damped Lyman-alpha systems in the universe. (iii) The redshift distribution of gamma ray bursts can, in principle, be used for studying the physical conditions of the universe before reionization epoch (which is otherwise a difficult task). (iv) It might be possible that the dark matter and dark energy arise from the same scalar field, provided the equation of state has a dependence on the length scale. The possibility of using the kinematical and geometrical measurements (such as supernova observations) for determining the nature and evolution of the dark energy is discussed.