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Benevento, Giampaolo (2020) Concordance or Tensions? Testing deviations from [Lambda]CDM cosmology in light of recent observations. [Ph.D. thesis]

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Abstract (italian or english)

The aim of this work is testing valid extensions or alternatives to the [Lambda]CDM model, aiming to address the problem of Dark Energy and to reconcile discrepancies between different observational probes. In order to investigate and put constraints on these theories, we employ different statistical and numerical tools and complementary cosmological probes.
In Chapter 2 we provide a general introduction about the standard Friedmann-Lemaitre-Robertson-Walker cosmological models. We introduce the main observable probes of the background dynamics of the Universe and discuss the evidence for an accelerated expansion. We discuss the hypothesis of a cosmological constant and the theoretical issues related to this hypothesis. We introduce the problem of the Hubble tension as the main open issue in the standard cosmological scenario. Finally, we develop the formalism for the description of linear cosmological perturbations that led to the formation of Large Scale Structure.
In Chapter 3 we briefly review possible alternative explanations to the current accelerated expansion of the Universe. We discuss how Solar System tests are able to strongly constrain modification to General Relativity and we show how this can be avoided through the presence of screening mechanisms. We introduce different theoretical frameworks that allow to describe very general classes of theories, starting from the Effective Field Theory of Dark Energy, to the Horndeski and Beyond-Horndeski models.
In Chapter 4 we review the theory of CMB anisotropies and discuss the main cosmological observables which can be used to probe the cosmological model. We focus on the possible signatures of Dark Energy and Modified Gravity which can be originated on early and late cosmic epochs.
In Chapter 5 we present our analysis on K-mouflage and K-mimic models. We discuss the phenomenology of the model, its mapping in the Effective Field Theory of Dark Energy and employ a Markov-Chain-Monte-Carlo method to estimate the model parameters, using data of CMB, CMB lensing, type Ia supernovae and different galaxy catalogues. We complement our results with Fisher matrix forecasts for future CMB surveys like CORE. We finally study the CMB-galaxy cross-correlation in K-mouflage, showing forecast for its detectability with future Euclid-Like and LSST-like surveys.
In Chapter 6 we study the phenomenology on the Galileon Ghost Condensate model and on its Beyond Horndeski extension. We analyze the impact of these models on the expansion history and on the growth of cosmic structures, employing complementary probes to constrain its parameters. Using appropriate model selection criteria, we compare these models to [Lambda]CDM.
In Chapter 7 we analyze the general phenomenology of perturbations in a dark fluid that becomes transiently important around matter-radiation equality. We develop and test a model, called Acoustic Dark Energy (ADE), that supplements the usual [Lambda]CDM components with an additional transient dark fluid whose energy density is relevant only near matter-radiation equality. We explain the critical role its sound speed plays in relieving the Hubble tension. We show that ADE models are favored over [Lambda]CDM, improving [chi]² by 12.7 for a simple canonical kinetic term with 2 additional parameters.
In Chapter 8 we discuss our results and draw a general conclusion.

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EPrint type:Ph.D. thesis
Tutor:Liguori, Michele
Supervisor:Bartolo, Nicola
Ph.D. course:Ciclo 32 > Corsi 32 > FISICA
Data di deposito della tesi:07 July 2020
Anno di Pubblicazione:2020
Key Words:Cosmology, Dark Energy, Modified Gravity, Cosmological Parameters
Settori scientifico-disciplinari MIUR:Area 02 - Scienze fisiche > FIS/05 Astronomia e astrofisica
Struttura di riferimento:Dipartimenti > Dipartimento di Fisica e Astronomia "Galileo Galilei"
Codice ID:12950
Depositato il:02 Feb 2021 10:47
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