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Modern cosmology has reached an important juncture, at which the ability to make measurements of unprecedented accuracy has led to conclusions that are a fundamental challenge to natural science. The discovery that, in our current best model, the dynamics of the Universe are completely dominated by unseen dark matter and dark energy can do little but completely alter the shape of physics research in the 21st Century. Unfortunately,much of our insight into these phenomenamust come from observations of visible matter alone; this raises serious problems, as the tracing of dark matter by visible matter is as yet poorly understood. Gravitational lensing offers strong prospects for probing the interwoven history of dark and visible matter, as mass in any form may be detected where it exists untraced by baryons. In this Thesis I describe advances made in the field of weak gravitational lensing, which constrains the properties of the matter distribution on cosmological scales using a statistical analysis of the coherent gravitational distortions of distant galaxy images. I summarize the development of gravitational flexion, a higher order extension to traditional weak lensing, and describe my work done to bring the study of flexion to a stage where it may be employed to make accurate cosmological measurements. I show how flexion is sensitive to matter structure on smaller physical scales than existing lensing techniques and, therefore, promises to shed new light upon key untested predictions of cosmological models if it can be measured to sufficient accuracy. I discuss the success of my efforts in this direction, and describe the issues to be encountered in the careful analysis of this subtle gravitational signal. This research has involved advances in many areas: the calculation of theoretical flexion predictions, the refinement of image analysis methods for accurate galaxy shape estimation, and the practical application of these new flexion techniques to extragalactic imaging data. The culmination of these efforts is a new maximum likelihood analysis of the galaxy-galaxy lensing signal in the Hubble Space Telescope Galaxy Evolution from Morphology and SEDs (GEMS) Survey, incorporating improvements and modifications necessary for the combination of flexion with traditional weak lensing measurements. The results of this work, and particularly the extent to which measurements of flexion provide extra cosmological insight, are discussed in detail. The conclusion is a summary of all that has been learned about the use of flexion as an accurate probe of cosmology, and a discussion of its prospects for answering some of the many questions that remain about dark matter. Within the next few year wide-area survey telescopes will begin imaging huge volumes of deep space, with the measurement of the gravitational lensing signal being given high priority in the analysis of these data. Within this context, the primary inquiry of this Thesis is the extent to which the application of flexion measurement techniques will help shed new light upon the unseen, and currently poorly understood, components of the Universe.

Li Baojiu = 宇宙学和新物理学的交叉领域 / 李宝九. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references (leaves 93-99). / Text in English; abstracts in English and Chinese. / Li Baojiu = Yu zhou xue he xin wu li xue de jiao cha ling yu / Li Baojiu. / Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Some Basic Conceptions in Cosmology --- p.2 / Chapter 1.1.1 --- "The Big Bang, Hubble's Law" --- p.2 / Chapter 1.1.2 --- The Cosmological Principle and Robertson-Walker Metric --- p.3 / Chapter 1.1.3 --- The Cosmological Redshift --- p.4 / Chapter 1.1.4 --- The Friedmann Equations --- p.4 / Chapter 1.2 --- Big Bang Nucleosynthesis --- p.5 / Chapter 1.3 --- Dark Energy --- p.9 / Chapter 2 --- "Branes, Varying Constants and BBN" --- p.16 / Chapter 2.1 --- A Brief Introduction to Theories Involving Extra Dimensions --- p.17 / Chapter 2.1.1 --- The Kaluza-Klein Theory --- p.18 / Chapter 2.1.2 --- Large Extra Dimensions --- p.19 / Chapter 2.1.3 --- Warped Extra Dimensions --- p.22 / Chapter 2.1.4 --- Universal Extra Dimensions --- p.24 / Chapter 2.1.5 --- Cosmology in a Brane World --- p.27 / Chapter 2.2 --- BBN and Varying Constants in Brane Models --- p.29 / Chapter 2.2.1 --- The Low Energy Effective Action in Brane Models --- p.30 / Chapter 2.2.2 --- BBN with a Varying Higgs VEV --- p.34 / Chapter 2.3 --- Numerical Results --- p.38 / Chapter 2.4 --- Discussion and Conclusions --- p.47 / Chapter 3 --- "Universal Extra Dimensions, Varying Constants and BBN" --- p.49 / Chapter 3.1 --- Introduction --- p.50 / Chapter 3.2 --- The Low Energy 4-Dimensional Effective Actions --- p.50 / Chapter 3.3 --- Radion Dependence of Fundamental Constants --- p.54 / Chapter 3.4 --- Variations of Quantities Relevant For BBN Calculation --- p.57 / Chapter 3.4.1 --- Neutron-proton Mass Difference --- p.57 / Chapter 3.4.2 --- Weak Interaction Rates --- p.58 / Chapter 3.4.3 --- Expansion Rate of the Universe --- p.58 / Chapter 3.4.4 --- Nuclear Reaction Rates --- p.59 / Chapter 3.5 --- Numerical Results --- p.64 / Chapter 3.6 --- Discussion and Conclusions --- p.70 / Chapter 4 --- Dark Energy as a Signature of Extra Dimensions --- p.74 / Chapter 4.1 --- Introduction --- p.75 / Chapter 4.2 --- The Underlying Higher Dimensional Theory --- p.75 / Chapter 4.3 --- The Cosmic Evolution in Different Eras --- p.79 / Chapter 4.3.1 --- The Blazing Era --- p.79 / Chapter 4.3.2 --- The Radiation Dominated Era --- p.83 / Chapter 4.3.3 --- The Matter Dominated Era --- p.84 / Chapter 4.4 --- A Realistic Cosmology --- p.85 / Chapter 4.5 --- Discussions and Conclusions --- p.92 / Bibliography --- p.93

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 93-98).

Thesis (Ph. D.)--University of Washington, 2005. / Vita. Includes bibliographical references (p. 103-111).

Next-generation cosmological surveys will demand an unprecedented understanding of the interplay between theoretical and observational aspects of weak gravitational lensing. This thesis presents a study of the parameter degeneracies and theoretical uncertainties which will affect weak lensing tests of cosmology beyond the standard paradigm. In particular, tests of alternative theories of gravity and of spatial curvature are considered. First, by considering linear-order departures from the standard gravitational theory of general relativity, a novel expression is derived for the weak lensing convergence power spectrum under alternative theories of gravity. Using this expression, degeneracies between gravitational parameters in weak lensing observations are explored, first with a focus on scale-independent parameterisations of gravity, then considering new physical scales introduced by alternative theories. The degeneracy-breaking offered by the combination of weak lensing and redshift-space distortions is shown to be robust to the time-dependence of the functions parameterising modified gravity. Next, the gravity-testing statistic EG is investigated, and a new theoretical expression for its observationally-motivated definition is presented. The theoretical uncertainty of EG is compared to forecast statistical errors, and found to be significant in the case of a more futuristic measurement. Predictions are then computed for EG under deviations from general relativity, and the ongoing utility of EG as a probe of gravity is discussed. Finally, an investigation is made of the potential for measuring or constraining the spatial curvature using weak lensing and complementary observables. The predicted constraint on the spatial curvature is forecast for a suite of upcoming surveys, and the effect of including parameters which may be degenerate with the spatial curvature is explored. It is found that upcoming observations are likely to constrain spatial curvature at a 10⁻³ level, but not to reach the best-case constraint of ~10⁻⁴.

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Orientador: Álvaro de Souza Dutra / Coorientador: Álvaro de Souza Dutra / Banca: Elias Leite Mendonça / Banca: Denis Dalmazi / Banca: Roldão da Rocha Júnior / Banca: José Abdala Helayë-Neto / Resumo: Dentro da cosmologia, o modelo ΛCDM é considerado, pela comunidade científica, como aquele que melhor descreve o universo. Todavia, tal modelo sofre de alguns males que ainda precisam ser sanados. Entre eles se destacam o problema da constante cosmológica e o problema da coincidência cósmica. Atribui-se, neste modelo, a expansão acelerada do universo a um ente de origem desconhecida, chamado de energia escura. Parte da solução destes problemas está intimamente ligado em saber a natureza da energia escura. Por outro lado, devido a propriedades intrínsecas do espinor ELKO, faz-se possível atribuir ao mesmo o papel de energia escura. Deste modo, constrói-se aplicações cosmológicas do ELKO que possibilitem a resolução completa ou parcial dos problemas mencionados. Estas aplicações consistem basicamente na análise do sistemas de equações de Friedmann oriundas da anexação do Lagrangeano do ELKO na ação de Einstein-Hilbert. Dentro desse sistema se insere a mão o possível decaimento do ELKO em outros elementos que constituem o universo. Com este se alivia o problema da coincidência cósmica, enquanto que se confirma que o ELKO pode figurar como energia escura por meio dos resultados do sistema geral. Ao fim do trabalho se observa uma outra aplicação do ELKO, desta vez no cenário cosmológico de Einstein-Cartan. Neste se mostra que o modelo cosmológico que contém o ELKO como energia escura, e na presença de termo de torção, é análogo ao modelo cosmológico Λ(t) / Abstract: In cosmology the ΛCDM model is the most accepted way to describe the universe. However, this model suffers some problems that have to be solved. Namely there are two of them which are attached in this thesis. They are the cosmic coincidence and the cosmological constant problem. Due this model it is possible to relate the universe's accelerated expansion to dark energy. Part of solving these problems pass through knowing the origin of dark energy. It is known that the spinor ELKO has some fundamental properties that able scientists to connect them to dark universe elements, e.g. dark energy. So, some applications of ELKO in cosmology have been made in order to explore this possibility and to solve those fundamental problems. These application are based on analyzing ELKO in dynamical systems formed by Friedmann's equations, where these equations comes from putting ELKO's Lagranian in the Einstein-Hilbert action. In this system it is inserted a term of decaying. With such term it is possible to alleviate cosmic coincidence problem. On the other hand it is also possible to justify ELKO as dark energy as wished at the beginning. Last but not least, another application of ELKO in cosmology has been investigated. For such case is was shown that, with some considerations and approximations, ELKO in cosmology allied with Einstein-Cartan formalism can mimic Λ(t) cosmology results / Doutor

Orientador: José Geraldo Pereira / Banca: Ruben Aldrovandi / Banca: Rogério Rosenfeld / Banca: Oliver Fabio Piatella / Banca: José Wadih Maluf / Resumo: Observações realizadas nas últimas três décadas confirmaram que o universo se encontra em um estado de expansão acelerada. Essa aceleração é atribuída à presença da chamada energia escura, cuja origem permanece desconhecida. A maneira mais simples de se modelar a energia escura consiste em introduzir uma constante cosmológica positiva nas equações de Einstein, cuja solução no vácuo é então dada pelo espaço de de Sitter. Isso, por sua vez, indica que a cinemática subjacente ao espaço-tempo deve ser aproximadamente governada pelo grupo de de Sitter SO(1,4), e não pelo grupo de Poincaré ISO(1,3). Nesta tese, adotamos tal argumento como base para a conjectura de que o grupo que governa a cinemática local é o grupo de de Sitter, com o desvio em relação ao grupo de Poincaré dependendo ponto-a-ponto do valor de um termo cosmológico variável. Com o propósito de desenvolver tal formalismo, estudamos a geometria de Cartan na qual o espaço modelo de Klein é, em cada ponto, um espaço de de Sitter com o conjunto de pseudo-raios definindo uma função não-constante do espaço-tempo. Encontramos que o tensor de torção nessa geometria adquire uma contribuição que não está presente no caso de uma constante cosmológica. Fazendo uso da teoria das realizações não-lineares, estendemos a classe de simetrias do grupo de Lorentz SO(1,3) para o grupo de de Sitter. Em seguida, verificamos que a estrutura da gravitação teleparalela--- uma teoria gravitacional equivalente à relatividade geral--- é uma geometria de Riemann-Cartan não linear. Inspirados nesse resultado, construímos uma generalização da gravitação teleparalela sobre uma geometria de de Sitter--Cartan com um termo cosmológico dado por uma função do espaço-tempo, a qual é consistente com uma cinemática localmente governada pelo grupo de de Sitter. A função cosmológica possui sua própria dinâmica e emerge na... / Abstract: Observations during the last three decades have confirmed that the universe momentarily expands at an accelerated rate, which is assumed to be driven by dark energy whose origin remains unknown. The minimal manner of modelling dark energy is to include a positive cosmological constant in Einstein's equations, whose solution in vacuum is de Sitter space. This indicates that the large-scale kinematics of spacetime is approximated by the de Sitter group SO(1,4) rather than the Poincaré group ISO(1,3). In this thesis we take this consideration to heart and conjecture that the group governing the local kinematics of physics is the de Sitter group, so that the amount to which it is a deformation of the Poincaré group depends pointwise on the value of a nonconstant cosmological function. With the objective of constructing such a framework we study the Cartan geometry in which the model Klein space is at each point a de Sitter space for which the combined set of pseudoradii forms a nonconstant function on spacetime. We find that the torsion receives a contribution that is not present for a cosmological constant. Invoking the theory of nonlinear realizations we extend the class of symmetries from the Lorentz group SO(1,3) to the enclosing de Sitter group. Subsequently, we find that the geometric structure of teleparallel gravity--- a description for the gravitational interaction physically equivalent to general relativity--- is a nonlinear Riemann--Cartan geometry.This finally inspires us to build on top of a de Sitter--Cartan geometry with a cosmological function a generalization of teleparallel gravity that is consistent with a kinematics locally regulated by the de Sitter group. The cosmological function is given its own dynamics and naturally emerges nonminimally coupled to the gravitational field in a manner akin to teleparallel dark energy models or scalar-tensor theories in general relativity. New in... / Doutor

Orientador: Maria Cristina Batoni Abdalla Ribeiro / Coorientador: Felipe Batoni Abdalla / Banca: Marcos Vinícius Borges Teixeira Lima / Banca: Laerte Sodré Junior / Resumo: Observações atuais do satélite Wilkinson Microwave Anisotropy Probe (WMAP) da Radiação Cósmica de Fundo (CMB) e estruturas de grande escala (LSS) têm permitido melhorar os estudos das anisotropias secundárias, especialmente o efeito Sachs-Wolfe Integrado (ISW). Usando a correlação cruzada entre a CMB e mapas da LSS, o sinal do efeito ISW pode ser detectado. Nós podemos usar o efeito ISW junto com o modelo cosmológico padrão (neste caso o Universo esta dominado pela constante cosmológica e a Matéria Escura Fria, ΛCDM) mais algoritmos numéricos para restringir os parâmetros em um modelo cosmológico com energia escura. Para diferentes casos com um único parâmetro livre de um model de Quintessência parametrizado,' w IND. 0' < 0 e 2,0 < 'w IND. a' <−2,0, podemos encontrar bins de largura [−1,926,−0,323] em 'w ind. 0' e [−0,855, 1,190]. Nestes intervalos, obtemos um sigma de nivel tomando o 68% da amostra que melhor se ajusta ao modelo cosmológico padrão / Abstract: Current observations of the Wilkinson Microwave Anisotropy Probe (WMAP) satellite of Cosmic Microwave Background (CMB) and Large Scale Structure (LSS) have allowed to improve studies of the secondary anisotropies, especially the Integrated Sachs-Wolfe effect (ISW). Using the cross-correlation between the CMB and LSS maps, the ISW effect signal can be detected. We can use the ISW effect together with standard cosmological model (in this case the Universe is dominated by the cosmological constant and Cold Dark Matter, ΛCDM) plus numerical algorithms to constrain the parameters in a cosmological model with dark energy. For cases different with a single free parameter of a parameterised Quintessence model, 'w ind. 0' < 0 and 2,0 < 'w ind. a' <−2,0, we can find bins of width [−1,926,−0,323] in 'w ind. 0' and [−0,855, 1,190] in wa. In these intervals, we obtain one sigma level by taking the 68% of the sample which best fit the standard cosmological model / Mestre