Doutorado em Astrofísica, Cosmologia e Gravitação
URI Permanente para esta coleção
Nível: Doutorado
Ano de início: 2016
Conceito atual na CAPES: 5
Ato normativo: Parecer 487/2018
Periodicidade de seleção: Semestral
Área(s) de concentração: Astronomia e Física
Url do curso: https://cosmologia.ufes.br/pt-br/pos-graduacao/PPGCosmo/detalhes-do-curso?id=1453
Navegar
Navegando Doutorado em Astrofísica, Cosmologia e Gravitação por Assunto "Cosmologia"
Agora exibindo 1 - 5 de 5
Resultados por página
Opções de Ordenação
- ItemModified gravity and large scale structure cosmology: a linear and non-linear treatment(Universidade Federal do Espírito Santo, 2022-06-10) Oliveira, Guilherme Brando de; Falciano, Felipe Tovar; https://orcid.org/0000000322631252; http://lattes.cnpq.br/7214193952056222; https://orcid.org/0000000308051905; Fabris, Julio Cesar; https://orcid.org/000000018880107X; http://lattes.cnpq.br/5193649615872035; Bragança, Vinicius Miranda; Quartin, Miguel Boavista; https://orcid.org/0000000158536164; http://lattes.cnpq.br/3080181268936724; Abramo, Luis Raul Weber; Wands, David GrahamThis thesis consists of a comprehensive study of beyond-ΛCDM cosmologies, in particular I investigate possible consequences of scalar-tensor theories of gravity on the Large Scale Structure of the Universe. Within the Standard Model of Cosmology, General Relativity is assumed to be the theory that describes gravity in all scales and this is supported by the highly accurate Astrophysical and Solar System tests. Notwithstanding, at cosmological scales, we still lack gravity tests with the same constraining power. Therefore, in addition to the motivation from the well-known conceptual problems of the Cosmological Constant, it is reasonable to investigate if General Relativity is the correct gravity theory at the largest scales of the Universe. In order to increase the accuracy of our cosmological tests of gravity, I develop numerical tools based on the linear and nonlinear regimes of cosmological perturbation theories, as well as a non-perturbative approach using quasi N-body simulations. I also present different ways of testing the large freedom introduced by modified theories of gravity in the parameter space. Indeed, modified gravity models cannot avoid introducing extra parameters besides the usual six cosmological parameters of the ΛCDM model. The main results of the thesis have been published in four papers cited along the text and I have tried to condensate them mainly in Chapters 3, 4 and 6. In chapter 3 I discuss the impact of modified gravity on cosmological observables such as the modifications Horndeski theories introduce in the growth and light propagation equations of motion. In particular, I perform a detailed analysis of the No Slip Gravity at the linear regime of structure formation. Then, I discuss how early modified gravity theories change the matter power spectrum at large and small scales. In Chapter 4, I start by analyzing the matter power spectrum at linear scales, namely how it is defined within ΛCDM and how massive neutrinos introduce a scale dependent on the growth function. Then, I introduce the formulation of the N-Body gauge, a specific coordinate system that facilitates the interpretation of Newtonian simulations within a relativistic framework, by consistently introducing the effects coming from photons, neutrinos and dark energy. As stage-IV LSS surveys will probe the Universe at increasingly large scales; it is imperative to include these species in our analysis inasmuch at large scales their imprint can be above the 1% threshold. I also present new cosmological tests of gravity by combining this framework with relativistic N-Body simulations. At the end I show how to correctly combine modified gravity effects and Newtonian simulations. In Chapter 5, I outline all the nonlinear mathematical tools have I have studied and developed during this project and on Chapter 6 I present the results of how we can construct computationally fast new numerical tools using all the new developments I have done in modified gravity, from linear to nonlinear scales. Chapter 7 ends the thesis with some conclusions and three future avenues I plan to pursue in the next few years.
- ItemProbing cosmology with an eye on Rubin : from strong lensing to the large scale structure of the universe(Universidade Federal do Espírito Santo, 2024-04-11) Oliveira, Renan Alves de; Ho, Shirley ; https://orcid.org/0000-0002-1068-160X; Makler, Martín; https://orcid.org/0000-0003-2206-2651; http://lattes.cnpq.br/6567844719949395; https://orcid.org/0000-0002-0200-3833; http://lattes.cnpq.br/1895596998416086; Abramo, Luis Raul Weber ; https://orcid.org/0000-0001-8295-7022; http://lattes.cnpq.br/4558796258762790; Bom, Clécio Roque de ; https://orcid.org/0000-0003-4383-2969; http://lattes.cnpq.br/5635352837026339; Velten, Hermano Endlich Schneider ; https://orcid.org/0000-0002-5155-7998; http://lattes.cnpq.br/0282590467459210; Marra, Valerio ; http://orcid.org/0000-0002-7773-1579; http://lattes.cnpq.br/6846011112691877In 2024, the Vera C. Rubin Observatory will begin observing the Universe for the next ten years. Two key cosmological observables that Rubin will probe are gravitational lensing and the large-scale structure of the Universe. In this thesis, we derive analytical solutions for strongly lensed images that can be useful for generating fast simulations and as a starting point in parameter searches for lens inversion. Then, we obtain an expression in closed form for the magnification cross-section, which can be used to predict the abundance of highly magnified sources. Next, we focus on real data and assemble an extensive compilation of Strong Lensing candidate systems from the literature containing over 30,000 unique objects. We cross-match this sample with the current major photometric and spectroscopic catalogs. As preparation for Rubin, we generate image cutouts for these systems in most current wide-field surveys with subarcsecond seeing, namely DES, HSC, KiDS, CFHTLens, RCSLens, and CS82. This sample dubbed the “Last Stand Before Rubin” (LaStBeRu), has a myriad of applications, from using archival data to selections for follow-up projects and training of machine learning algorithms. As an application, we have performed a test of General Relativity (GR) with these data, combining information from strong lensing and velocity dispersions, which allow one to set constraints on the Post-Newtonian parameter γPPN. From the LaStBeRu database, we were able to provide the first independent test of γPPN from previous results and for the first time only for systems identifiable in ground-based images. We can obtain the most stringent constraint on γPPN by combining these data with the current samples. Moreover, we have obtained new spectroscopic data for systems selected from LaStBeRu, which were used to obtain the first end-to-end determination of γPPN. It is also the first determination derived purely from ground-based data and the first to use self-consistent priors. Our results are consistent with GR at the ∼ 1-σ level and with the previous results from the literature. Finally, in the context of the large structure, we present two neural emulators capable of making fast predictions for the density, displacement, and velocity fields of dark matter particles without necessarily having to run expensive N-body simulations. We compared these emulators with another fast method for the same task, showing that neural emulators provide the best results
- ItemPushing the boundaries of modern cosmology: physics beyond the Copernican principle(Universidade Federal do Espírito Santo, 2022-08-16) Torres, David Francisco Camarena; Marra, Valerio; https://orcid.org/0000000277731579; http://lattes.cnpq.br/6846011112691877; https://orcid.org/0000000171650439; http://lattes.cnpq.br/2093261235489631; Piattella, Oliver Fabio; https://orcid.org/0000000345580574; http://lattes.cnpq.br/5707156831919279; Amendola, Luca; https://orcid.org/0000-0002-0835-233X; http://lattes.cnpq.br/7512327723238183; Sapone, Domenico; https://orcid.org/; http://lattes.cnpq.br/; Clarkson, ChrisThe standard paradigm of modern cosmology relies on a set of fundamental assumptions that simplify and make possible the modeling of the Universe. Among these critical hypotheses, there is the presumption that we do not occupy a special place in the Uni- verse, the so-called Copernican principle. The assumption of this principle constrains the degrees of freedom allowed by the theory, and, in particular, within the framework of the General Theory of Relativity, leads to a spatially homogeneous and isotropic space-time. Here, we present a program to observationally test the Copernican princi- ple and study the cosmological applications of inhomogeneous cosmologies. Under the assumption of a spherically inhomogeneous extension of the standard model and using the latest cosmological data, we test the Copernican principle by placing constraints on radial deviations of the spatially homogeneous and isotropic space-time. We also forecast the precision with which future surveys, such as DES, Euclid and LSST, will be able to test the Copernican principle and test their ability to detect any possible violations. Furthermore, we investigate if a local void could explain away the 5σ discrepancy between the early and late times determinations of the Hubble constant. Our goal is to take the first steps to extend the boundary of the standard paradigm of modern cosmology, and, in particular, to develop a suitable framework for the development of physics beyond the Copernican principle.
- ItemStatistical tools in cosmology: model selection and covariance matrix comparison(Universidade Federal do Espírito Santo, 2021-10-04) Ferreira, Tassia Andrade; Marra, Valerio; https://orcid.org/0000000277731579; http://lattes.cnpq.br/6846011112691877; https://orcid.org/0000000340163763; http://lattes.cnpq.br/0780205870619041; Sobreira, Flávia; https://orcid.org/0000-0002-7822-0658; http://lattes.cnpq.br/2432352931378666; Vitenti, Mariana Penna Lima; https://orcid.org/0000-0003-2652-0891; http://lattes.cnpq.br/6692996818863210; Makler, Martin; https://orcid.org/0000000322062651; http://lattes.cnpq.br/6567844719949395; Dodelson, Scott; https://orcid.org/0000-0002-8446-3859; http://lattes.cnpq.br/9816136210217542Albeit ΛCDM’s fame as the concordance model, there are many interesting myster ies worth exploring, such as the nature of dark energy. Here, we test the viability of several classes of scenarios of the dark sector with linear and non-linear inter acting terms. To do so, we use a Bayesian model selection with data from type Ia supernovae, cosmic chronometers, cosmic microwave background and two sets of baryon acoustic oscillations measurements: 2-dimensional angular measurements (BAO2), and 3-dimensional angle-averaged measurements (BAO3). On the other hand, we consider covariance matrices, which are important tools for parameter estimation. We explore ways of compressing them by analysing their eigenvalues and signal-to-noise ratio, by employing a tomographic compression and, lastly, with the Massively Optimized Parameter Estimation and Data compression (MOPED). We find that MOPED is a powerful tool in the comparison of covariance matrices and, towards that end, we build a python code that uses a fast Monte Carlo simulation to obtain comprehensible values for differences between two covariance matrices. This method thus eliminates the need for a full cosmological analysis as we relate its output to the corresponding parameter constraints.
- ItemThe redshift drift as a new cosmological probe(Universidade Federal do Espírito Santo, 2024-09-19) Dutra, Pedro Henrique Bessa Rodrigues; Durrer, Ruth; https://orcid.org/0000-0001-9833-2086; Marra, Valerio; https://orcid.org/0000-0002-7773-1579; Marttens, Rodrigo vom; Piattella, Oliver Fabio; Koksbang, Sofie Marie; Martins, CarlosWith the advent of precision cosmology and the next generation of telescopes and sur veys, observations will allow the standard cosmological model to be tested in old and new regimes with unprecedented accuracy, and the data will demand accurate the oretical models of cosmological phenomena in order to be properly interpreted and processed. Theorists are reassessing old and new probes that allow the current cosmo logical paradigm to be tested to its limits. One promising new probe, the measurement which is one of the main objectives of the ELT ANDES spectrograph, is the cosmic redshift drift. One of the theoretical predictions of cosmological models based on Robertson-Walker metrics is the cosmic redshift drift, which measures the real-time rate of change of the spectra of far away sources, and is a generic consequence of cosmological models where the expansion rate is non-constant. Its observation provides a model independent way to measure the time variation of the Universe’s expansion and as such, an independent test of the late-time acceleration phase of the Universe and the existence of a cosmo logical constant. In this thesis we study the redshift drift in realistic cosmological models containing inhomogeneities in the !CDM paradigm. We derive for the first time a gauge-invariant expression for the redshift drift and its power spectrum, and implement the redshift drift f luctuation power spectrum numerically through Einstein-Boltzmann codes and using n-body simulations, providing a solid theoretical foundation for future measurements and observations of the redshift drift in !CDM cosmology and beyond.