DYNAMICS OF COSMOLOGICAL MODELS USING EXOTIC FLUID IN GENERAL RELATIVITY AND ITS MODIFIED GRAVITY

Abstract

The present thesis studies cosmological models in which exotic fluids, matter creation mecha nisms, bulk viscous effects, and modified gravity frameworks are used to describe the late-time evolution of the Universe. The work is motivated by the need to understand cosmic acceler ation, observational tensions, and possible alternatives to the standard cosmological picture. The thesis combines theoretical modelling with observational constraints and compares the proposed models with the standard ΛCDM scenario. The first chapter introduces the background of modern cosmology, including the cosmolog ical principle, relativistic cosmology, dark energy, Chaplygin-type fluids, matter creation, bulk viscosity, cosmological parameters, observational data sets, and statistical tools. The follow ing chapters present the main research contributions on generalized and variable Chaplygin gas models, matter creation cosmology, bulk viscous effects, and extensions in f(Q) gravity. The final chapter summarizes the conclusions, future research directions, and broader relevance of the thesis. This thesis has been prepared in a chapter-wise form so that each research problem is in troduced, developed, constrained, and discussed in a self-contained manner, while remaining connected to the central theme of exotic-fluid cosmology in General Relativity and modified gravity.