The theoretical explanation of cosmic acceleration is nowadays one of the biggest puzzles in cosmology. Within the standard cosmological model (LCDM) the expansion is sourced by the vacuum energy... Show moreThe theoretical explanation of cosmic acceleration is nowadays one of the biggest puzzles in cosmology. Within the standard cosmological model (LCDM) the expansion is sourced by the vacuum energy associatedto the Cosmological Constant L. Despite its simplicity, the Cosmological Constant presents various unresolved problems from both the theoretical and the observational side.However, even if we dismiss these puzzles, the study of theoretical alternatives to LCDM is still of primary importance. In fact, the wealth and quality of cosmological data that we are expecting for thenext decade will allow us to test gravity on cosmological scales with unprecedented accuracy. This will give us the chance to investigate many of our theoretical ideas and to assess the strength of the standard model of cosmology on the largest scales.In this thesis we present different approaches that we can adopt to study modifications of gravity by means of cosmology. Show less
The focus of the dissertation "Aspects of cosmic acceleration" is the study of possible mechanisms responsible for the late-time accelerated expansion of the universe. It has 5 main chapters. In... Show moreThe focus of the dissertation "Aspects of cosmic acceleration" is the study of possible mechanisms responsible for the late-time accelerated expansion of the universe. It has 5 main chapters. In the first chapter I have given an overview of modern cosmology. Particularly, an introduction to cosmological perturbation theory, and a general overview of the cosmological standard model, as well as an overview to beyond-standard-model scenarios is presented. Chapter two discusses cosmological models based on the so-called alpha-attractor framework. Chapter three is dedicated to the study of constraints imposed by gravitational wave observations on the so-called doubly-coupled massive bimetric gravity theory. Chapter four studies the cosmological stability of the so-called massive mimetic gravity theory. Finally, Chapter five studies the effect of the Symmetron gravity on the so-called splashback radius of dark matter halos. Show less
