Explaining the physical origin of cosmic acceleration still poses a challenge to modern cosmology. On one hand, observational evidence corroborating this phenomenon is compelling and continuously becoming stronger and stronger. On the other hand a physical explanation for it is still missing. Cosmic acceleration might be explained by a cosmological constant having the same effect of vacuum energy. Indeed cosmological observations point in this direction and the cosmological constant is a cornerstone of the standard cosmological model. This explanation, however, suffers from several naturalness problems that reflect the fact that, while a cosmological constant is allowed in the gravitational sector by symmetry arguments, there is no theory for the gravitational effect of quantum vacuum. To address this issue, or at least to have an intuition of the phenomenology related to the solution of this problem, one might want to add other dark fluids to the cosmic budget or modify the laws of gravity on large scales to drive the accelerated expansion of the universe. In this thesis we develop and exploit a threefold approach to the study of the phenomenological aspects of cosmic acceleration with the aim of systematizing the investigation of models beyond the standard one. The first path that we shall follow is that of quantifying the level of agreement of cosmological observations, within the standard cosmological model; this will allow us to determine whether there is already some indication that this model might be inappropriate in describing present day observations. Then we shall move along the second path to study parametrized approaches to the phenomenology of Dark Energy and Modified Gravity theories. We de- velop the relevant tools to exploit an Effective Field Theory description for this phenomenon and we investigate some of its observational consequences. At last we shall move along the third path that consists in testing specific non-standard models. Exploiting the unifying power of the Effective Field Theory approach, we study the cosmological implications and corresponding data constraints on two f(R) models and on Horava gravity. Overall we find that, already at present, cosmological observations are precise enough to substantially improve our knowledge about the space of Dark Energy and Modified Gravity models. While doing so we developed the relevant tools to perform massive and systematic studies of non-standard cosmologies aiming at explaining the physical origin of Cosmic Acceleration with present data and the next generation of cosmological surveys.
|Titolo:||The Threefold Way to Cosmological Tests of Gravity|
|Data di pubblicazione:||24-giu-2016|
|Appare nelle tipologie:||8.1 PhD thesis|