Submitted by Liliane Ferreira (ljuvencia30@gmail.com) on 2018-08-21T12:44:31Z No. of bitstreams: 2 Dissertação - Lucas Elias Vieira - 2018.pdf: 1438523 bytes, checksum: 81df75730e0ab41f69b4619af81cd7a2 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2018-08-22T12:42:43Z (GMT) No. of bitstreams: 2 Dissertação - Lucas Elias Vieira - 2018.pdf: 1438523 bytes, checksum: 81df75730e0ab41f69b4619af81cd7a2 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2018-08-22T12:42:43Z (GMT). No. of bitstreams: 2 Dissertação - Lucas Elias Vieira - 2018.pdf: 1438523 bytes, checksum: 81df75730e0ab41f69b4619af81cd7a2 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2018-07-13 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In this work, we study topological defects in classical field theory aiming applications in cosmology. Topological and non-topological solutions were investigated in two dimensions, where we also analyzed the stability of some of these. We consider models of one and two real scalar fields, whose solutions were obtained via quadrature, BPS and orbit methods. The stability of these solutions also were investigated in some cases. In order to apply scalar field theory in cosmology, we revisit some topics of general relativity, such that the principle of equivalence, Einstein's field equations and Schwarzschild's solution for Einstein's equation. We also present some topics in cosmology, relevant to the present work, such that the cosmological principle, Hubble's law and cosmological inflation. We discuss the solutions of the Einstein's equations in the FRW metric in the so-called Hot Big Bang model-the universe composed of matter and radiation. In order to solve some problems of initial conditions of the universe, we introduce the inflationary theory, which supposes that the primordial universe was underwent an accelerated expansion guided by a scalar field. In sequence, we introduce the standard cosmological model, which states that the universe is in accelerated expansion driving by a cosmological constant, named dark energy, which constitutes about seventy percent of the universe energy. Finally, we present a first order formalism for cosmology and discuss two model describing the standard and tachyonics dynamics for scalar field that represent the dark energy. / Neste trabalho foram abordadas soluções do tipo defeitos topológicos em teoria clássica de campos. Foram investigadas soluções topológicas e não topológicas em duas dimensões, onde também analisamos a estabilidade de algumas destas. Consideramos modelos de um e dois campos escalares reais, onde utilizamos os métodos de quadratura, BPS e das órbitas para obter soluções. Com o intuito de aplicar a teoria de campos escalares em cosmologia, introduzimos a teoria da relatividade geral, falando sobre o princípio da equivalência, equações de campo de Einstein e solução de Schwarzschild para as equações de Einstein. Abordamos alguns tópicos em cosmologia, onde enunciamos o princípio cosmológico, lei de Hubble e inflação cosmológica. Resolvemos as equações de Einstein na métrica FRW considerando o universo composto de matéria e radiação denominado modelo Big Bang quente. Com o objetivo de resolver alguns problemas de condições iniciais do universo, introduzimos a teoria inflacionária, a qual propõe que o universo primordial sofreu uma expansão acelerada guiada por um campo escalar. Após mostrar como a teoria da inflação corrige tais problemas, apresentamos o modelo cosmológico padrão, o qual afirma que o universo está em expansão acelerada e utiliza uma constante cosmológica como guia da expansão, tal constante neste cenário representa a denominada energia escura que compõe aproximadamente setenta por cento do universo. Finalmente, nós apresentamos o formalismo de primeira ordem para cosmologia e discutimos dois modelos descrevendo dinâmicas padrão e taquiônica para o campo escalar, representando a energia escura.

La dynamique de formation des structures de l'Univers est habituellement décrite dans le cadre du modèle standard de Cosmologie. Cependant, pour que les observations cosmologiques soient cohérentes avec le modèle standard, il est nécessaire de supposer l'existence d'une grande proportion d'éléments de nature inconnue dans le contenu de l'Univers. Pour tenter de résoudre cette énigme, nous ne considèrerons pas d'autres sources dans le contenu de l'Univers que celles ordinaires et resterons dans le cadre de la Relativité Générale. Nous développerons néanmoins une description plus réaliste de la formation de structures dans le cadre de la théorie d'Einstein. Ainsi, contrairement au modèle standard de Cosmologie, nous ne supposerons pas que l'Univers moyenné est une solution homogène et isotrope des équations d'Einstein. Lors de mon travail sous la direction de Thomas Buchert, j'ai participé au développement d'un formalisme perturbatif permettant une description plus réaliste de la dynamique de l'espace-temps. J'ai également contribué à l'obtention de solutions relativistes à la partie gravitoélectrique des équations d'Einstein en généralisant les solutions perturbatives newtoniennes. Ces travaux ont été réalisés dans le cadre d'une approche lagrangienne intrinsèque, évitant ainsi de définir les grandeurs physiques sur un fond plat. L'approche gravitoélectromagnétique que j'ai adoptée m'a permis une interprétation nouvelle et performante des solutions des équations d'Einstein. Enfin, j'ai étudié l'impact de la topologie sur la dynamique des ondes gravitationelles à l'aide d'une description globale de l'hypersurface spatiale, permise par des théorèmes mathématiques puissants / The dynamics of structure formation in the Universe is usually described by Newtonian numerical simulations and analytical models in the frame of the Standard Model of Cosmology. The structures are then defined on a homogeneous and isotropic background. Such a description has major drawbacks since, to be self-consistent, it entails a large amount of dark components in the content of the Universe. To address the problem of dark matter and dark energy, we will neither suppose that exotic sources contribute to the content of the Universe, nor that General Relativity is obsolete. We will develop a more realistic description of structure formation in the frame of General Relativity and thus no longer assume that the average model is a homogeneous-isotropic solution of the Einstein equations, as claimed by the Standard Model of Cosmology. During my work under the supervision of Thomas Buchert, I contributed to the development of the perturbative formalism that enables a more realistic description of spacetime dynamics. In the framework of the intrinsic Lagrangian approach, which avoids defining physical quantities on a flat background, I contributed to the building of relativistic solutions to the gravitoelectric part of the Einstein equations from the generalization of the Newtonian perturbative solutions. Moreover, the gravitoelectromagnetic approach I worked with has provided a new understanding of the dynamics of the analytical solutions to the field equations. Finally, treating globally the spatial manifold, I used powerful mathematical tools and theorems to describe the impact of topology on the dynamics of gravitational waves

L'un des plus grands problèmes ouverts de la cosmologie moderne est l'origine de l'expansion accélérée de l'Univers, découverte en 1998. L'explication théorique la plus simple repose sur l'introduction d'une constante cosmologique $Lambda$. Ce modèle, connu sous le nom de $Lambda$CDM, est en accord avec les différentes observations liées à l'expansion accélérée. Cependant, il présente des problèmes d'ordre théorique. Par conséquent, plusieurs alternatives, connues collectivement sous le nom de {it modèles d'énergie noire}, ont été proposées pour expliquer cette accélération. Plusieurs d'entre eux restent viables, car leurs {it backgrounds} cosmologiques ne présentent pas de signatures identifiables. Par contre, les effets sur les phénomènes perturbatifs sont plus spécifiques à chacun de ces modèles. Dans cette thèse, nous explorons les caractéristiques particulières de la croissance des perturbations de matière à l'ordre linéaire dans les théories $f(R)$ avec un regard complémentaire sur les modèles chameleon. La paramétrisation du taux de croissance de la matière en termes d'une fonction $gamma$ permet d'identifier une signature très spécifique de ces modèles en comparaison avec le modèle $Lambda$CDM. Une étude supplémentaire a permis de trouver une dépendance en échelle explicite, nommée {it dispersion}, dans la croissance des perturbations. Des observations plus précises pourraient permettre de faire la différence entre ces différents modèles selon la présence de ces caractéristiques. / One of the most important open issues in modern cosmology is the origin of the accelerated expansion of the Universe, observed in 1998. The simplest theoretical explanation relies on the introduction of a cosmological constant $Lambda$. This model, known as $Lambda$CDM, agrees with all the different observations connected to the accelerated expansion. However, it presents some theoretical issues. As a result, several alternatives, known collectively under the name of {it dark energy models}, have been proposed to explain this acceleration. Several among them remain viable, since their cosmological backgrounds do not show any identifiable signature. On the other hand, effects on the perturbative level are more specific to each model. In this thesis, we explore the particular characteristics of the growth of linear matter perturbations in $f(R)$ theories, with a complementary look on chameleon models. The parameterization of the growth rate in terms of a $gamma$ function allows us to identify a very specific signature of these models in comparison with the $Lambda$CDM model. A subsequent study allowed us to find an explicit scale dependance, known as {it dispersion}, in the growth of perturbations. More precise observations could enable us to distinguish between dark energy models according to the presence of this type of feature.

>Magister Scientiae - MSc / Measuring the evolution of the abundance of galaxy clusters puts constraints on cosmological parameters like the cosmological density parameter m, σ8 and the dark energy equation of state parameter, w. Current observations that promise to give large cluster counts and their properties are those that rely on the Sunyaev-Zeldovich effect (SZE) from clusters. We study the contamination of the SZ signals from galaxy clusters by cluster infrared (IR) galaxies and particularly faint IR galaxies. We use the Millennium simulation database to extract galaxy clusters and deduce contaminant IR fluxes using the star formation rate - IR luminosity relations. We use the IR spectral energy distribution(SED) to obtain the monochromatic fluxes at 145 GHz, 217 GHz and 265 GHz, which are the observation frequencies of the Atacama Cosmology Telescope (ACT). Taking ACT as a case study, we selected all clusters with Mvir ≥ 2 × 1014 M⊙, and consider all galaxies in a cluster with star formation rate sfr ≥ 0.2 M⊙yr−1 as IR galaxies. From the fluxes of these selected sources, we compute their contribution to the SZE temperature fluctuations.We find that the galaxies in clusters have a non-neglible contribution to the SZ signals.In massive and rich clusters the contribution can be as high as 100 μK at z = 0.36,which is substantial when compared to the thermal SZE of & 270μK for such clusters.This effect can be reduced significantly if proper modelling of IR sources is done to pick out the point sources within clusters. We also find that irrespective of the mass range,the average contaminant temperature fluctuation T can be modelled as a power-law: T = Czm, where z is the redshift, m = 1.8 ± 0.07 and C takes on a range of values(0.008 to 0.9) depending on the cluster mass and the observation frequency respectively.We also study some properties of simulated galaxy clusters like substructures in clusters,2D projected distributions and number density profiles, which are all discussed in the results.

Ce travail de thèse se sépare en deux volets. Le premier volet concerne l'étude de l'homogénéité de l'univers, et le second une mesure de l'échelle BAO, qui constitue une règle standard permettant de mesurer l'évolution du taux d'expansion de l'univers. Ces deux analyses reposent sur l'étude de la structuration (ou clustering) des quasars des relevés BOSS et eBOSS, qui couvrent la gamme en redshift 0,9 < z < 2,8. Les mesures des observables caractérisant la structuration de l'univers aux grandes échelles sont très sensibles aux effets systématiques, nous avons donc étudiés ces effets en profondeur. Nous avons mis en évidence que les sélections de cibles quasars BOSS et eBOSS ne sont pas parfaitement homogènes, et corrigé cet effet. Au final, la mesure de la fonction de corrélation des quasars nous a permis de mesurer le biais des quasars sur la gamme en redshift 0,9 < z < 2,8. Nous obtenons la mesure actuelle la plus précise du biais, b = 3,85 ± 0,11 dans la gamme 2,2 < z < 2,8 pour le relevé BOSS, et b = 2,44 ± 0,04 dans la gamme 0,9 < z < 2,2 pour le relevé eBOSS. Le Principe Cosmologique stipule que notre univers est isotrope et homogène à grande échelle. Il s'agit d'un des postulats de base de la cosmologie moderne. En étudiant la structuration à très grande échelle des quasars, nous avons prouvé l'isotropie spatiale de l'univers dans la gamme 0,9 < z < 2,8, indépendamment de toute hypothèse et cosmologie fiducielle. L'isotropie spatiale stipule que l'univers est isotrope dans chaque couche de redshift. En la combinant au principe de Copernic, qui stipule que nous ne nous situons pas à une position particulière dans l'univers, permet de prouver que notre univers est homogène aux grandes échelles. Nous avons effectué une mesure de la dimension de corrélation fractale de l'univers, D₂(r), en utilisant un nouvel estimateur, inspiré de l'estimateur de Landy-Szalay pour la fonction de corrélation. En corrigeant notre estimateur du biais des quasars, nous avons mesuré (3 - D₂(r)) = (6,0 ± 2,1) x 10⁻⁵ entre 250 h⁻¹ Mpc et 1200 h⁻¹ Mpc pour le relevé eBOSS, dans la gamme 0,9 < z < 2,2. Pour le relevé BOSS, nous obtenons (3 - D₂(r)) = (3,9 ± 2,1) x 10⁻⁵, dans la gamme 2,2 < z < 2,8. De plus, nous montrons que le modèle Lambda-CDM décrit très bien la transition d'un régime structuré vers un régime homogène. D’autre part, nous avons mesuré la position du pic BAO dans les fonctions de corrélation des quasars BOSS et eBOSS, détecté à 2,5 sigma dans les deux relevés. Si nous mesurons le paramètre α, qui correspond au rapport entre la position du pic mesuré et la position prédite par une cosmologie fiducielle (en utilisant les paramètres Planck 2013), nous mesurons α = 1,074 pour le relevé BOSS, et α = 1,009 pour le relevé eBOSS. Ces mesures, combinées uniquement à la mesure locale de H₀, nous permettent de contraindre l'espace des paramètres de modèles au-delà du Lambda-CDM. / This work consists in two parts. The first one is a study of cosmic homogeneity, and the second one a measurement of the BAO scale, which provides a standard ruler that allows for a direct measurement of the expansion rate of the universe. These two analyses rely on the study of quasar clustering in the BOSS and eBOSS quasar samples, which cover the redshift range 0.9 < z < 2.8. On large scales, the measurement of statistical observables is very sensitive to systematic effects, so we deeply studied these effects. We found evidences that the target selections of BOSS and eBOSS quasars are not perfectly homogeneous, and we have corrected this effect. The measurement of the quasar correlation function provides the quasar bias in the redshift range 0.9 < z < 2.8. We obtain the most precise measurement of the quasar bias at high redshift, b = 3.85 ± 0.11, in the range 2.2 < z < 2.8 for the BOSS survey, and b = 2.44 ± 0.04 in the range 0.9 < z < 2.2 for the eBOSS survey. The Cosmological Principle states that the universe is homogeneous and isotropic on large scales. It is one of the basic assumptions of modern cosmology. By studying quasar clustering on large scales, we have proved ''spatial isotropy'', i.e. the fact that the universe is isotropic in each redshift bins. This has been done in the range 0.9 < z < 2.8 without any assumption or fiducial cosmology. If we combine spatial isotropy with the Copernican Principle, which states that we do not occupy a peculiar place in the universe, it is proved that the universe is homogeneous on large scales. We provide a measurement of the fractal correlation dimension of the universe, D₂(r), which is 3 for an homogeneous distribution, and we used a new estimator inspired from the Landy-Szalay estimator for the correlation function. If we correct our measurement for quasar bias, we obtain (3 - D₂(r)) = (6.0 ± 2.1) x 10⁻⁵ between 250 h⁻¹ Mpc and 1200 h⁻¹ Mpc for eBOSS, in the range 0.9 < z < 2.2. For BOSS, we obtain (3 - D₂(r)) = (3.9 ± 2.1) x 10⁻⁵, in the range 2.2 < z < 2.8. Moreover, we have shown that the Lambda-CDM model provide a very nice description of the transition from structures to homogeneity. We have also measured the position of the BAO peak in the BOSS and eBOSS quasar correlation functions, which yield a 2,5 sigma detection in both surveys. If we measure the α parameter, which corresponds to the ratio of the measured position of the peak to the predicted position in a fiducial cosmology (here Planck 2013), we measure α = 1.074 for BOSS, and α = 1.009 for eBOSS. These measurements, combined only with the local measurement of H₀, allows for constraints in parameter space for models beyond Lambda-CDM.

La propagation des ondes acoustiques dans le plasma primordial a laissé son empreinte sous la forme d'un pic dans la fonction de corrélation à deux points de la densité de matière. Ce pic d'oscillations acoustiques de baryons (BAO) constitue une échelle standard permettant de déterminer certains paramètres des différents modèles cosmologiques.Dans ce manuscrit de thèse, nous présentons une mise à jour de la mesure de BAO à un redshift z=2.40, à l'aide de la fonction de corrélation croisée entre deux traceurs des fluctuations primordiales de densité de matière: les quasars de SDSS-III (BOSS) et leurs fluctuations d'absorption du flux des forêts Lyman-α. Ces fluctuations tracent la distribution d'hydrogène neutre dans le milieu intergalactique (IGM).Cette étude constitue le premier développement d'un ajustement entièrement physique de la fonction de corrélation croisée; il prend notamment en compte la physique des quasars et la présence d'éléments plus lourds que l'hydrogène dans l'IGM. Nous y présentons également les premières simulations de notre analyse. Celles-ci nous permettent de valider l'ensemble de la procédure de mesure de l'échelle BAO.Cette étude mesure la distance de Hubble et la distance de diamètre angulaire avec respectivement une précision de 2% et 3% (intervalle à 1 σ). Nous combinons nos résultats avec d'autres mesures de BAO à des redshifts plus faibles et trouvons la densité de matière noire et d'énergie noire dans le cadre de deux différents modèles cosmologiques: ΛCDM et oΛCDM. / The acoustic wave propagation in the primordial plasma left its imprint in the two-point correlation function of the matter density field. This baryonic acoustic oscillation (BAO) peak builds up a standard ladder allowing us to infer some parameters of the different cosmological models.In this thesis manuscript we present an update of the BAO measurement at a redshift z=2.40, from the cross-correlation function between two tracers of the primordial matter density fluctuations: quasars of SDSS-III (BOSS) and their Lyman-α-forest absorption fluctuations. These fluctuations trace the neutral hydrogen distribution in the intergalactic medium (IGM).This study gives the first developpment of the full physical fit of the cross-correlation. Among other effects, it takes into account quasar physics and the distribution of IGM elements heavier than hydrogen. We also present the first simulations of our analysis. They allow us to validate the overall data analysis leading to the BAO measurement.This study measures the Hubble distance and the angular diameter distance at the 2%$ and 3%$ precision level respectivelly (1 σ interval). We combine our results with other BAO measurements at lower redshifts and find the dark matter density and dark energy density in the framework of two different cosmological models: ΛCDM et oΛCDM.

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<p>This thesis addresses two separate naturalness issues which generically come to bear on physical theories with large extra dimensions, and so a gravity scale much lower than the Planck scale. The first is related to the observed stability of the proton, wherein we determine the relevant constraints on an additional gauge boson which conserves baryon number. Although several such proposals have been previously considered, our analysis is distinctive in its interest in lighter gauge boson masses (which naturally arise in such models), and in its focus on the dependence of constraints due to kinetic mixing effects. The second is related to the main purpose of large extra dimensions---namely, to address the smallness of the observed vacuum energy---wherein we compute the leading-order quantum corrections to the four-dimensional (4D) vacuum energy resulting from loops of extra-dimensional fields. We compute the contributions from bulk scalars (spin 0), fermions (spin 1/2), and gauge fields (spin 1) in a flux-stabilized, spheroidal extra-dimensional geometry whose rugby-ball shape is due to two codimension-2 branes---one at each pole. (We also obtain the corresponding beta functions for both bulk and brane operators.) These results are then combined to obtain the net contribution from various multiplets in the context of a particular supersymmetric extra-dimensional model that has been shown to give a vanishing result for the 4D vacuum energy at the classical level. Surprisingly, we find that supersymmetry can be preserved dynamically at one loop in the case of identical branes, without arranging any particular relationship between the brane parameters. Perturbing away from the case of identical branes is shown to give a positive 1-loop contribution to the 4D vacuum energy whose size is set by the radius of the extra dimensions.</p> / Doctor of Philosophy (PhD)

Masters of Science / Observations that push the boundaries have historically fuelled scientific breakthroughs, and these observations frequently involve phenomena that were previously unseen and unidentified. Data sets have increased in size and quality as modern technology advances at a record pace. Finding these elusive phenomena within these large data sets becomes a tougher challenge with each advancement made. Fortunately, machine learning techniques have proven to be extremely valuable in detecting outliers within data sets. Astronomaly is a framework that utilises machine learning techniques for anomaly detection in astronomy and incorporates active learning to provide target specific results. It is used here to evaluate whether machine learning techniques are suitable to detect anomalies within the optical astronomical data obtained from the Dark Energy Camera Legacy Survey. Using the machine learning algorithm isolation forest, Astronomaly is applied on subsets of the Dark Energy Camera Legacy Survey (DECaLS) data set. The pre-processing stage of Astronomaly had to be significantly extended to handle real survey data from DECaLS, with the changes made resulting in up to 10% more sources having their features extracted successfully. For the top 500 sources returned, 292 were ordinary sources, 86 artefacts and masked sources and 122 were interesting anomalous sources. A supplementary machine learning algorithm known as active learning enhances the identification probability of outliers in data sets by making it easier to identify target specific sources. The addition of active learning further increases the amount of interesting sources returned by almost 40%, with 273 ordinary sources, 56 artefacts and 171 interesting anomalous sources returned. Among the anomalies discovered are some merger events that have been successfully identified in known catalogues and several candidate merger events that have not yet been identified in the literature. The results indicate that machine learning, in combination with active learning, can be effective in detecting anomalies in actual data sets. The extensions integrated into Astronomaly pave the way for its application on future surveys like the Vera C. Rubin Observatory Legacy Survey of Space and Time.