Yukawa-type screening inherent in higher dimensional gravity and cosmology

Abstract

At the intersection of gravitation and cosmology, a study of the large-scale structure of the Universe, and particularly, the search for a general relativistic approach appropriate for formulating structure formation at all-scales makes up the principle objective of this thesis. It introduces a scheme that combines the characteristics of such an approach, namely, the cosmic screening approach towards all-scale cosmological perturbations, with the screening of gravity emerging through a distinct mechanism as part of the relativistic perturbation theory. Subsequently, it presents an effective screening length (the effective interaction range of Yukawa gravity) for gravitational interactions at cosmological scales, which matches the size of the largest-yet-observed cosmic structure, and thereby, argues for homogeneity and isotropy in the Universe not from few hundred megaparsecs, but from a few gigaparsecs on. The analysis is first carried out for the flat LCDM model, but later it is extended to involve curved spaces with the same energy components. A comparison of Newtonian approximation and Yukawa behavior is performed in terms of single particle gravitational force calculations relevant to structure formation simulations, and impacts of periodicity on the Yukawa force are investigated to reveal the extent of deviations from the free-boundary problem. Finally, metric coefficients of certain multidimensional f(R) models are studied in the weak-field limit, which also acquire corrections in the form of Yukawa potentials subject to constraints form the inverse-square law experiments.