A STUDY ON EVOLUTION AND DYNAMICS OF DARK ENERGY MODELS IN COSMOLOGY

Abstract

Cosmology is a branch of science which deals with the study of the origin of Universe, its evolution, and its eventual fate. Cosmology has been classified into two categories in contemporary science: Physical cosmology and Observational Cosmology. The study of the Universe’s formation, evolution, and the physics behind it, is known as physical cosmology. Observational cosmology investigates the direct evidence of the Universe’s formation and structure using telescopes and other tools. Cosmological models are studied using the combination of theories and observations. These models incorporate ideas as well as data gathered from observations. Cosmology integrates developments from a wide range of scientific fields, such as relativity, quantum mechanics, particle physics, nuclear physics, astrophysics, and plasma physics. Nicolaus Copernicus’ discovery that the Earth rotates around the Sun in the early 1500s marked the beginning of modern cosmology. Isaac Newton’s discovery in the late 1600s that objects in space functioned in accordance with the same rules of physics as objects on Earth was an additional breakthrough. Early in the 20th century, Albert Einstein’s theory of relativity provided a model of spacetime, establishing the way to modern physical cosmology. Contemporary cosmologists assert that the Universe is made up of far more than the ordinary matter we encounter daily. Most scientists believe that a significant portion of the Universe is composed of Dark energy and Dark matter. According to this theory, about two-thirds of the Universe is composed of dark energy. The dark energy is believed to be the force that defies gravity and permits the Universe to expand- a phenomenon known as cosmic acceleration. According to this concept, dark matter makes up an additional 26% of the cosmos. Scientists are unable to directly detect this hypothetical kind of matter since it does not emit or absorb light and only interacts with regular matter through gravity. The most plausible and effective candidate of dark energy is the cosmological vii constant introduced by Albert Einstein. Several alternative models have been proposed to explain the Universe’s observed accelerated expansion which includes scalar field theories, Chaplygin gas, holographic dark energy and Ricci dark energy, and several other dark energy models. The decaying vacuum energy density and bulk viscosity have recently been investigated as additional potential explanations for the universe’s current accelerated expansion. The objective of this thesis is to investigate how decaying vacuum and bulk viscosity contribute to the explanation of dark energy phenomena in the context of a spatially homogenous and isotropic flat Friedmann-Lemaître-Robertson-Walker metric in general relativity and its modified theories. Using observational data, we fit the model to the proposed model and extract the relevant information on the decaying vacuum energy density and bulk viscosity. The first chapter serves as an introduction. The research that was published as research articles in reputable, peer-reviewed publications served as the basis for chapters 2–6. The conclusion and future directions of the thesis work are covered in the final chapter. Each chapter starts with an overview of the work accomplished in that chapter.