Thesis (Ph. D.)--University of Texas at Austin, 2006. / Vita. Includes bibliographical references.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009. / Title from title screen (site viewed June 26, 2009). PDF text: x, 153 p. : ill. (some col.) ; 9 Mb. UMI publication number: AAT 3350442. Includes bibliographical references. Also available in microfilm and microfiche formats.

Thesis (M.S.)--Miami University, Dept. of Physics, 2008. / Title from first page of PDF document. Includes bibliographical references (p. 39-40).

Inaug.--diss.--Heidelberg. / Lebenslaauf.

Boucle gravité quantique (LQG) est une tentative pour résoudre le problème de la gravité quantique. Boucle cosmologie quantique (LQC) est une tentative d'appliquer LQG à la cosmologie précoce. Le but de LQC est de se connecter LQG avec des observations. Il est très difficile d'observer les effets de la gravité quantique parce que la densité d'énergie énorme est très probablement nécessaire. Ceci est exactement pourquoi l'Univers est choisi comme une étape pour rechercher des phénomènes de gravité quantique.Le résultat central de LQC est que la grande singularité bang est remplacé par un gros rebond. Toutefois, ce ne sont pas quelque chose qui est possible d'observer aujourd'hui. Pour cette raison, nous avons étudié la façon dont les perturbations cosmiques sont affectées par LQC. Nous avons utilisé l'approche dite d'algèbre déformée, et nous avons calculé les spectres obtenus pour les deux perturbations scalaires et tenseurs. Les spectres que nous avons trouvé ne sont pas compatibles avec l'observation. Cependant cela ne peut abeille considérée comme très forte preuve contre LQG car il y a trop d'hypothèses sur le chemin. Plutôt cela est le résultat de cette interprétation spécifique de LQC.Nous avons également étudié la dynamique de fond (la partie homogène des équations) de LQC. Depuis lent-roll inflation est essentielle pour expliquer de nombreuses caractéristiques de l'univers, y compris le CMB, nous voulons savoir si lent-roll inflation est compatible avec LQC. Nous avons constaté que, en effet, il est. Si un champ d'inflation potentiel carré est ajouté à la théorie, le rebond va lever l'énergie potentielle suffisante pour fournir environ 145 e-plis de lent-roll inflation. Toutefois, lorsque anisotropies sont pris en compte, le montant de l'inflation diminue, et peut même disparaître complètement s'il y a trop de cisaillement au moment du rebond.Nous avons dérivé l'équation Friedman modifié pour anisotrope LQC. Cela nous a permis d'étudier anisotrope LQC pas seulement numériquement, mais aussi analytiquement, qui nous a donné une compréhension beaucoup plus complète de la situation que ce qui était connu auparavant.Enfin, nous avons étudié certains aspects géométriques de l'espace de Sitter, qui a donné lieu à deux considérations très différentes. Tout d'abord nous avons constaté que nous pouvons, pour une théorie générale de la cosmologie modifiée et sous certaines hypothèses assez conservatrices, tirer la dynamique d'un univers spatialement incurvée, étant donné la dynamique d'un un espace plat. Cela est pertinent dans les théories telles que LQC, où il est plus facile de trouver la solution plate que celle incurvée. Deuxièmement, nous proposons un mécanisme possible pour l'origine et la renaissance de l'Univers. / Loop quantum gravity (LQG) is an attempt to solve the problem of quantum gravity. Loop quantum cosmology (LQC) is an attempt to apply LQG to early cosmology. The purpose of LQC is to connect LQG with observations. It is very hard to observe any quantum gravity effects because enormous energy density is most likely required. This is exactly why the early Universe is chosen as a stage to search for quantum gravity phenomena.The central result of LQC is that the big bang singularity is replaced by a big bounce. However this is not something that is possible to observe today. For this reason, we have investigated how cosmic perturbations are affected by LQC. We have used the so called deformed algebra approach, and have calculated the resulting spectrums for both scalar and tensor perturbations.The spectrums that we have found are not compatible with observation. However this can not bee taken as very strong evidence against LQG since there are too many assumptions on the way. Rather this is a result for this specific interpretation of LQC.We have also studied the background dynamics (the homogenous part of the equations) of LQC. Since slow-roll inflation is essential in explaining many features of the universe, including the CMB, we want to know if slow-roll inflation is compatible with LQC. We have found that, indeed, it is. If a square potential inflation field is added to the theory, the bounce will lift the potential energy enough to provide around 145 e-folds of slow-roll inflation. However, when anisotropies are taken into account, the amount of inflation decreases, and can even disappear completely if there is too much shear at the time of the bounce.We have derived the modified Friedman equation for anisotropic LQC. This has allowed us to study anisotropic LQC not just numerically, but also analytically, which has given us a much more comprehensive understanding of the situation than what was known before.Finally, we have studied some geometric aspects of de Sitter space, which has resulted in two very different considerations. Firstly we found that we can, for a general theory of modified cosmology and under some quite conservative assumptions, derive the dynamics for a spatially curved universe, given the dynamics of a spatially flat one. This is relevant in theories such as LQC, where it is easier to find the flat solution than the curved one. Secondly, we propose a possible mechanism for the origin and rebirth of the Universe.

Le projet de recherche consiste à observer en laboratoire la radiation de Hawking, cette prédiction stupéfiante de l'astrophysicien anglais Stephen Hawking faite en 1974 : les trous noirs ne sont pas noirs. Autrement dit, ils n'absorbent pas tout ce qui est à leur portée mais émettent un rayonnement. En plus des complications du fait que ces objets célestes sont à des milliers d'années-lumière, ce rayonnement est tellement faible que cela reviendrait à essayer d'entendre un murmure dans un concert de rock. Mais William Unruh, en 1981, a proposé une solution : utiliser des systèmes hydrodynamiques qui présentent les mêmes équations mathématiques qu'en astrophysique. Plus précisément, dans notre cas, nous utilisons la correspondance entre la propagation des ondes lumineuses au voisinage d'un trou noir et celles des ondes de surface dans un contre-courant rendu inhomogène par la présence d'un obstacle immergé. Pour cela, une compréhension approfondie de la mécanique des ondes de surface est nécessaire (bathymétrie variable, vorticité, non-linéarités…). Du côté technique, une méthode de mesure de surface libre a été développée et optimisée. / The aim of the PhD is the observation the Hawking radiation in the laboratory, this astounding prediction of the English astrophysicist Stephen Hawking made in 1974: black holes are not black. In other words, they do not absorb anything within reach but emit a radiation. In addition to the complications of the fact that these celestial objects are thousands of light years away, this radiation is so weak that it would be like trying to hear a whisper in a rock concert. But William Unruh, in 1981, proposed a solution: to use hydrodynamic systems which have the same mathematical equations as in astrophysics. More precisely, in our case, we use the correspondence between the propagation of light in the vicinity of a black hole and surface waves propagation on a inhomogeneous countercurrent (due to the presence of a submerged obstacle). For this, a thorough understanding of the surface waves physics is necessary (variable bathymetry, vorticity, non-linearities ...). On the technical side, a free surface measurement method has been developed and optimized.

SANTOS, Victor Pereira do Nascimento. Aspectos da quebra de simetria de Lorentz e não-comutatividade em modelos de gravitação. 2014. 138 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2014. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-06-23T21:01:04Z No. of bitstreams: 1 2014_tese_vpnsantos.pdf: 12919592 bytes, checksum: 11e84d851c538b7c5f9b8a6cae752fef (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-06-23T21:06:01Z (GMT) No. of bitstreams: 1 2014_tese_vpnsantos.pdf: 12919592 bytes, checksum: 11e84d851c538b7c5f9b8a6cae752fef (MD5) / Made available in DSpace on 2015-06-23T21:06:01Z (GMT). No. of bitstreams: 1 2014_tese_vpnsantos.pdf: 12919592 bytes, checksum: 11e84d851c538b7c5f9b8a6cae752fef (MD5) Previous issue date: 2014 / In this work we will present some aspects from quantum gravity. We introduce the problem of quantum gravity and some proposals to tackle it. In particular, our investigations touch upon three general subjects: noncommutative geometry, violations of Lorentz symmetry and inflationary cosmology. In noncommutative geometry we made two proposals for possible experimental verifications: in the former we calculate the luminosity of spherically symmetric black-hole where its event horizon was modelled by a noncommutative space; in the latter we investigate the thermodynamical properties of the graphene in the presence of a magnetic field, verifying the influence of the noncommutativity. Regarding the Lorentz symmetry violation we showed its physical viability of extra-dimensional scenarios, by calculating the graviton mass in the four-dimensional effective theory. We also calculate the influence of the Lorentz symmetry breaking in the gravitational sector in four dimensions, by means of quantum corrections to the Newtonian potential. Finally, in cosmology we present a preliminar study on the measure problem, which is related to how natural the inflationary process is. We propose using the Hamiltonian formulation for evaluating the probability of inflation in a scenario where the scalar field describing the inflation is non-minimally coupled to the gravitational field, finding the the viability of this particular model when compared to observed data. / Neste trabalho iremos apresentar alguns aspectos de gravitação quântica. Introduzimos o problema da gravitação e algumas propostas para atacá-lo. Em particular, nossas investigações tocam três temáticas gerais: geometria não-comutativa, violação da simetria de Lorentz e cosmologia inflacionária. Em geometria comutativa fizemos duas propostas distintas para possíveis limitações experimentais: em uma calculamos a luminosidade de um buraco-negro modelando o seu horizonte de eventos por um espaço não-comutativo; e na outra calculamos as propriedades termodinâmicas do grafeno na presença de um campo magnético, verificando a influência da não-comutatividade. No que toca a quebra da simetria de Lorentz, mostramos a viabilidade física de cenários de dimensões extras, através do cálculo da massa do gráviton na teoria efetiva quadridimensional. Também calculamos a influência da quebra de simetria no setor gravitacional em quatro dimensões, através de correções quânticas ao potencial gravitacional. Finalmente, em cosmologia apresentamos um estudo preliminar sobre o problema da medida, que se relaciona com a probabilidade de que se tenha o processo de inflação independente das condições iniciais do sistema. Propusemos usar a formulação Hamiltoniana para o cálculo dessa probabilidade em um sistema onde o campo escalar é acoplado não-minimamente ao campo gravitacional, e assim verificar a viabilidade do modelo quando confrontado com dados observacionais.

Neste trabalho relata-se a produção de um conjunto de oficinas, com foco na formação continuada de professores, mas também com o objetivo de atingir leigos interessados no assunto: Gravitação Universal. As oficinas foram ministradas como parte do OEI – Observatório Educativo Itinerante, em cinco módulos distintos mas relacionados. As atividades foram elaboradas à luz das ideias de Lev Vygotsky, sob uma perspectiva sociocultural da construção do conhecimento. O foco das atividades reside na evidenciação de processos de construção dos modelos explicativos para os movimentos do Sistema Solar e as interações gravitacionais entre os principais astros. As reflexões decorrentes da aplicação das atividades aponta: (1) que o material é versátil e utilizável em diferentes contextos; (2) os assuntos abordados em especial nos módulos 1 e 2, devido a sua complexidade conceitual, exigem mais tempo do que o inicialmente previsto; (3) as atividades podem ser extraídas do contexto da produção e utilizadas independentemente, desde haja uma contextualização inicial, (4) um diferencial em relação a outras produções similares, é que contém discussões detalhadas sobre o que se pode esperar como resultados e por quê, visando a auxiliar professores com lacunas em sua formação; e (5) a utilização do referencial mostrou-se adequada e produtiva, pois propiciou reflexões e identificação de caminhos explicativos tanto na elaboração do material quanto na análise das concepções dos participantes. / This study is about the production of a set of workshops focusing on Continuing Education for teachers and aiming to achieve general people who are interested in Universal Gravitation. Workshops were carried out as part of the Itinerant Educational Observatory (OEI) in five distinct sections which were related to each other. Activities were formulated based on Lev Vygotsky’s ideas through a sociocultural perspective of knowledge construction. The focus of activities is the disclosure of construction processes of explanatory models for the solar system motions and the gravitational interaction among main stars. Reflections resulting from the implementation of activities show that (1) material is versatile and useful in different contexts; (2) subjects addressed - mainly in modules 1 and 2 - require more time than the originally planned due to notion complexity; (3) activities can be extracted from production context and used independently since there is initial contextualization; (4) divergence regarding other similar productions is that they contain detailed discussions on why and what can be expected as results attempting to help teachers with educational gaps; and (5) references proved to be satisfactory and productive since they led to reflection and explanatory path identification in both preparation of material and analysis of participants’ conceptions.

Orientador: Prof. Dr. André Gustavo Scagliusi Landulfo / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2015.

Orientador: Denis Dalmazi / Coorientador: Alessandro L. R. dos Santos / Banca: Elias Leite Mendonça / Banca: Fabrício Augusto Barone Rangel / Resumo: Neste trabalho abordamos de forma introdutória o tratamento de sistemas singulares, em especial as teorias de Maxwell, Proca e Fierz-Pauli, e obtemos resultados originais para a família de modelos de spin-2 massivos do tipo não-Fierz-Pauli. Tendo como ferramenta principal o método de Dirac para sistemas vinculados, escrevemos a densidade de hamiltoniana primária do modelo LnF P, obtemos seus vínculos primários, secundários, terciários e quartenários, assim como os multiplicadores de Lagrange. Calculamos também o número de graus de liberdade independentes e mostramos a positividade da hamiltoniana reduzida / Abstract: In this work, we approach in an introductory way the treatment of singular systems, especially the theories of Maxwell, Proca and Fierz-Pauli, and obtain original results for the non-Fierz-Pauli family of massive spin-2 models. Having as main tool the Dirac method for constrained systems, we write the primary Hamiltonian density of the LnF P model, obtain their primary, secondary, tertiary and quaternary constraints, as well as Lagrange multipliers. We calculate the number of independent degrees of freedom of the model and demonstrate the positivity of the reduced Hamiltonian / Mestre