Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Investigamos inicialmente o problema da obtenção de uma gravitação newtoniana modificada no caso da teoria da Relatividade Geral. Na sequência, encontramos uma solução geral com simetria esférica para um campo gravitacional fraco no contexto da Teoria de Brans-Dicke. Esta solução é independente de qualquer condição de coordenada. Então, para uma escolha conveniente da função f(r) na métrica de Brans-Dicke, exibimos uma fórmula modificada para a gravitação newtoniana, a qual pode descrever a gravidade em uma escala de comprimento pequena. Discutimos os resultados em comparação com o caso da Relatividade Geral / We investigate initially the problem of obtaining a modified newtonian gravitation in the case of General Relativity theory. Following, we find a general solution with spherical symmetry for a weak gravitational field in the context of Brans-Dicke theory. This solution is independent of any coordinate condition. Then, for a convenient choice of the function f(r) in Brans-Dicke metric, we exhibit a modified formula to newtonian gravity, which can describe gravity in a small length scale. We discuss the results in comparison with the case of General Relativity

Orientadores: Alberto Vazquez Saa, Marcelo Moraes Guzzo / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-24T01:44:37Z (GMT). No. of bitstreams: 1 Froes_AndreLuisDelvas_D.pdf: 13866800 bytes, checksum: 096d2e613867ddb45ba06cca87c00dec (MD5) Previous issue date: 2013 / Resumo: Na presente tese, após revisão do estado da arte da cosmologia observacional, dos modelos de blindagem cosmológica para campos escalares e de modelos vetoriais para energia escura, foi apresentada a pesquisa original do projeto. Ela consistiu na elaboração do primeiro modelo de blindagem cosmológico aplicável a campos vetoriais, por meio de uma modificação conforme na Relatividade Geral, dependente do módulo do campo. Nos meios onde a densidade é elevada, o campo vetorial oscila em torno de zero, enquanto em meios de baixa densidade ele possui um valor não nulo. Como resultado, o campo vetorial não afeta a evolução no Universo primordial nem gera uma quinta força ou modificações detectáveis na gravitação local. O mecanismo também pode ser utilizado para esconder violações de Lorentz em pequenas escalas. A evolução cosmológica do modelo é estudada em detalhes / Abstract: In this thesis, after a review on the state of the art on observational cosmology, screening mechanisms for scalar fields and vector field models for dark energy, the original research of this project is presented. It consisted in the creation of the first screening mechanism for vector fields, by means of a conformal modification of General Relativity, dependent on the norm of the field. In high density environments, the vector field oscillates around zero, while in low density environments it has a non-null value. As a result, the vector field doesn\'t affect the evolution in the early Universe, nor generates a fifth force or detectable modifications in local gravity. The mechanism can be used as well to hide Lorentz violations in small scales. The cosmological evolution is studied in detail / Doutorado / Física / Doutor em Ciências

Alla spelutvecklare har någonting att vinna på att kunna ge spelaren tydligare minnen av spelvärldar. I denna uppsats undersöks hur plattformsmoment kan användas för att förstärka mentala kartor. Respondenter har letat sig igenom en labyrint baserad på spelet Brain Fudge med olika grader av gravitation, och resultatet tyder på att besvärligare plattformsutmaningar gör det svårare för spelare att få en bild av spelvärlden som helhet. / Every game developer stands to gain from giving players clearer memories from game worlds. This paper examines how platform challenges can be used to support mental maps. Test subjects were tasked with navigating a maze based on the game Brain Fudge with varying degrees of gravity, and results imply that more cumbersome platform challenges make it more difficult for players to map the game world as a whole.

Une théorie de gravitation quantique propose de décrire l'interaction gravitationnelle à toutes les échelles de distance et d'énergie. Cependant, comprendre l'émergence de notre espace-temps classique reste un problème toujours ouvert. Cette thèse s'y attaque en gravité quantique à boucles à partir d'outils de l'information quantique.Ceci est fait en plusieurs étapes. La gravité quantique à boucles étant toujours une théorie en cours de développement, un point de vue pragmatique est adopté en étudiant une classe d'état physique du champ gravitationnel, motivée à la fois par des intuitions simples et les résultats de la physique à N corps. Une analyse de la reconstruction de la géométrie à partir des corrélations peut être faite et des leçons peuvent être tirées sur la forme de la dynamique fondamentale. Dans un second temps, la physique des sous-systèmes est analysée en commençant d'abord par évaluer l'entropie d'intrication entre l'intérieur et l'extérieur de la région, permettant ainsi de retrouver la loi holographique de l'entropie des trous noirs et donnant une forme possible des états holographiques de la théorie. Plusieurs dynamiques de la frontière, vu comme un système isolé ou ouvert, sont ensuite analysées, éclairant de nouveau la forme de la dynamique fondamentale. Enfin, la dernière étape de ces recherches étudie la dynamique de la frontière en interaction avec un environnement formé des degrés de liberté (de matière ou gravitationnels) formant le reste de l'Univers et la décohérence sur la frontière qu'il induit. Ceci permet de discuter la transition quantique/classique et de mettre en lumière, dans un modèle donné, les états pointeurs de la géométrie. / A quantum theory of gravitation aims at describing the gravitational interaction at every scales of energy and distance. However, understanding the emergence of our classical spacetime is still an open issue in many proposals. This thesis analyzes this problem in loop quantum gravity with tools borrowed from quantum information theory.This is done in several steps. Since loop quantum gravity is still under construction, a pragmatic point of view is advocated and an ansazt for physical states of the gravitational field is studied at first, motivated from condensed matter physics and simple intuitions. We analyze the proposal of reconstructing geometry from correlations. Lessons on the quantum dynamics and the Hamiltonian constraint are extracted. The second aspect of this work focuses on the physics of sub-systems and especially the physics of their boundary. We begin by calculating the entanglement entropy between the interior and the exterior of the region, recovering the holographic law known from classical black hole physics. Then different boundary dynamics are studied, both in the isolated and open cases, which shed lights again on the fundamental dynamics. Finally, the last aspect of this research studies the dynamics of the boundary interacting with an environment whose degrees of freedom (gravitational or matter) forming the rest of the Universe and especially the decoherence it induces. This allows to discuss the quantum to classical transition and understand, in a given model, the pointer states of geometry.

In this thesis, several new aspects of asymptotic symmetries have been exploited.Firstly, we have shown that the asymptotic symmetries can be enhanced tosymplectic symmetries in three dimensional asymptotically Anti-de Sitter (AdS) space-time with Dirichletboundary conditions. Such enhancement providesa natural connection between the asymptotic symmetries in the far region i.e. closeto the boundary) and the near-horizon region, which leads to a consistenttreatment for both cases. The second investigation in three dimensional space-time is to study theEinstein-Maxwell theory including asymptotic symmetries, solutionspace and surface charges with asymptotically flat boundary conditionsat null infinity. This model allows one to illustrate several aspectsof the four dimensional case in a simplified setting. Afterwards, we givea parallel analysis of Einstein-Maxwell theory in the asymptotically AdScase.Another new aspect consists in demonstrating a deep connection between certainasymptotic symmetry and soft theorem. Recently, a remarkable equivalence wasfound between the Ward identity of certain residual (large) U(1) gauge transformations and the leadingpiece of the soft photon theorem. It is well known that the softphoton theorem includes also a sub-leading piece. We have proven thatthe large U(1) gauge transformation responsible for the leading soft factorcan also explain the sub-leading one.In the last part of the thesis, wewill investigate the asymptotic symmetries near the inner boundary. Asa null hypersurface, the black hole horizon can be considered as an innerboundary. The near horizon symmetries create “soft” degrees of freedom. Wehave generalised such argument to isolated horizon and have shown that those “soft” degreesof freedom of an isolated horizon are equivalent to its electric multipolemoments. / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Quasars at high redshift provide direct information on the mass growth of supermassive black holes (SMBHs) and, in turn, yield important clues about how the universe evolved since the first (Pop III) stars started forming. Yet even basic questions regarding the seeds of these objects and their growth mechanism remain unanswered. The anticipated launch of eROSITA and ATHENA is expected to facilitate observations of high-redshift quasars needed to resolve these issues. In this paper, we compare accretion-based SMBH growth in the concordance Lambda CDM model with that in the alternative Friedmann-Robertson-Walker cosmology known as the R-h = ct universe. Previous work has shown that the timeline predicted by the latter can account for the origin and growth of the greater than or similar to 10(9) M-circle dot highest redshift quasars better than that of the standard model. Here, we significantly advance this comparison by determining the soft X-ray flux that would be observed for Eddington-limited accretion growth as a function of redshift in both cosmologies. Our results indicate that a clear difference emerges between the two in terms of the number of detectable quasars at redshift z greater than or similar to 7, raising the expectation that the next decade will provide the observational data needed to discriminate between these two models based on the number of detected high-redshift quasar progenitors. For example, while the upcoming ATHENA mission is expected to detect similar to 0.16 (i.e., essentially zero) quasars at z similar to 7 in R-h = ct, it should detect similar to 160 in Lambda CDM-a quantitatively compelling difference.

Ce travail de thèse se concentre sur l'approche non-perturbative canonique à la formulation d'une théorie quantique de la gravitation dans le cadre de la Gravitation quantique à boucles (LQG), répondant à deux problèmes majeurs. Dans la première partie, nous étudions la possible quantification, dans le cadre de la LQG, de la gravité en trois dimensions avec constante cosmologique et nous essayons de prendre contact avec autres approches de quantification déjà existantes dans la littérature. Dans la deuxième partie, nous nous concentrons sur une application très importante de la LQG: la définition et le comptage des états microscopiques d'un ensemble en mécanique statistique qui fournit une description de l'entropie des trous noirs. Notre analyse s'appuie fortement sur et s'étend à un traitement manifestement SU(2) invariant les travaux fondateurs de Ashtekar et al. / This thesis work concentrates on the non-perturbative canonical approach to the formulation of a quantum theory of gravity in the framework of Loop Quantum Gravity (LQG), addressing two major problems. In the first part, we investigate the possible quantization, in the context of LQG, of three dimensional gravity in the case of non-vanishing cosmological constant and try to make contact with alternative quantization approaches already existing in the literature. In the second part, we concentrate on a very important application of LQG: the definition and the counting of microstates of a statistical mechanical ensemble which provides a description and accounts for the black hole entropy. Our analysis strongly relies on and extends to a manifestly SU(2) invariant treatment the seminal work of Ashtekar et al.

Orientador: Alberto Vazquez Saa / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-08-04T02:11:29Z (GMT). No. of bitstreams: 1 Dadam_Fabio_M.pdf: 999114 bytes, checksum: 86eea1cd6f96a55892393c5ee86c320f (MD5) Previous issue date: 2005 / Resumo: Oscilações de buracos negros adquiriram importância nos últimos anos devido a possibilidade de se comprovar a existência de tais corpos celestes por meio da detecção da radiação gravitacional emitida por eles. Nesse trabalho, o estudo da propagação de ondas de diferentes tipos incidentes em um buraco negro é apresentado sob o ponto de vista matematico. Inicialmente, são usados elementos de Geometria Diferencial a fim de se estabelecer a estrutura matemática da gravitação e, a partir de um conjunto de hipóteses, determinase uma família de soluções das Equações de Einstein que caracteriza os buracos negros (Schwarzschild, Reissner-Nordstrom, Kerr e Kerr-Newman). As Equações de Teukolsky, que governam as perturbações de buracos negros, são obtidas com a ajuda do formalismo de Newman-Penrose e transformadas em uma equação de onda unidimensional. Obedecendo a condições de fronteira especificas, soluções dessa equação para frequências complexas são então determinadas a partir de diferentes métodos semi-analiticos / Abstract: In the past few years, black hole oscillations became a very interesting research area mainly due to the possibility of proving the existence of such celestial bodies through the gravitational radiation emitted by them. In this work, the study of the propagation of different kinds of incident waves on a black hole is presented under the mathematical point of view. Initially, elements of differential geometry are used to establish the mathematical structure of gravitation and, under certain hypotheses, a family of solutions to the Einstein equations is obtained, describing the black holes (Schwarzschild, Reissner-Nordstr¨om, Kerr and Kerr-Newman). Teukolsky equations, which govern the black hole perturbations, are obtained with the aid of Newman-Penrose formalism and transformed to a one-dimensional wave equation. According to certain boundary conditions, solutions of this equation for complex frequencies are determined from different semi-analytic methods / Mestrado / Geometria / Mestre em Matemática

Orientadores: Alberto Vazquez Saa, Marcus Aloizio Martinez de Aguiar / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-28T09:56:07Z (GMT). No. of bitstreams: 1 Depetri_GabrielaIunes_D.pdf: 7529104 bytes, checksum: 4925754e8306e25b65371018747949bf (MD5) Previous issue date: 2015 / Resumo: Nesta tese estudamos, através dos métodos de Melnikov, o comportamento de dois sistemas dinâmicos que são exemplos paradigmáticos de integrabilidade em Mecânica Clássica, quando sujeitos a perturbações: (i) o pêndulo plano simples, no caso em que o pivô oscila harmonicamente ao longo de um eixo inclinado em relação à direção vertical; e (ii) o problema de Kepler, no caso em que a massa do corpo que gera o campo gravitacional possui momento de quadrupolo. Para o pêndulo simples parametricamente excitado ao longo de uma direção inclinada, analisamos a ocorrência de caos homoclínico, e também de oscilações subharmônicas, com o objetivo de comparar os nossos resultados com aqueles conhecidos para o caso em que a excitação ocorre ao longo da direção vertical. Verificamos que o critério para a ocorrência de caos homoclínico é numericamente muito próximo em ambos os casos, mas em relação à ocorrência de soluções oscilatórias subharmônicas notamos uma diferença relevante devido à quebra de simetria nas equações do movimento do sistema: enquanto para o caso vertical a condição de Melnikov garante apenas a existência de oscilações subharmônicas de ordem par, nada se podendo afirmar em relação às subharmônicas de ordem ímpar, para o caso inclinado ela garante a ocorrência de todo o espectro de ressonâncias. Sabemos que apesar de alguns autores reportarem a ocorrência de oscilações subharmônicas de ordem ímpar no caso vertical, estas são muito raras e difíceis de ser encontradas, ao contrário do que acontece com as oscilações subharmônicas de ordem par. Entretanto, neste trabalho mostramos, através de simulações numéricas e dados experimentais, que no caso inclinado elas podem ser encontradas trivialmente em regiões de ressonância, provavelmente porque as bacias de atração dessas órbitas são de natureza diferente em cada caso. Os dados experimentais apresentados nesta tese foram tomados no Laboratório de Fenômenos Não-Lineares (LFNL) do Instituto de Física da Universidade de São Paulo (IFUSP), em colaboração com o Prof. Dr. José Carlos Sartorelli. Para o problema de Kepler, as inomogeneidades na distribuição da massa do corpo que gera o campo gravitacional são descritas através de expansão multipolar. Sabemos o termo de dipolo mantém o sistema integrável. O termo de quadrupolo, por sua vez, pode provocar a ocorrência de caos no sistema. Em um trabalho de 2001, Géron e Letelier afirmam, baseados em simulações numéricas, que no caso em que a perturbação é oblata, o sistema é integrável, enquanto se a perturbação é prolata, o sistema pode apresentar caos. Entretanto, em um trabalho mais recente, Letelier it et al mostram, também numericamente, que ambos os casos podem apresentar trajetórias caóticas. Com o nosso trabalho, resolvemos esta inconsistência na literatura, determinando que a ocorrência de caos de fato não depende do tipo da deformação. Nosso resultado está de acordo com o caso mais geral estudado na literatura / Abstract: In this PhD thesis we study, through the Melnikov methods, the behaviour of two dynamical systems that are paradigms of integrability in Classical Dynamics, when subject to perturbations: (i) the planar simple pendulum, in the case that the pivot oscillates harmonically along a tilted direction; and (ii) the Kepler problem, in the case that the mass of the body generating the gravitational field is not homogeneous, but instead presents a quadrupole moment term. To the simple pendulum parametrically excited along a tilted direction, we analyze the occurence of homoclinic chaos, and also of subharmonic oscillatory solutions, willing to compare our results with those already known in the literature in the case the excitation is along the vertical direction. We verified the criterium to the occurence of homoclinic chaos is numerically very close in both cases, but considering the occurence of subharmonic oscillatory orbits we noted an important difference due to the symmetry breaking of the equations of motion describing the system: while in the vertical case the Melnikov conditions can only assure the occurence of even subharmonic oscillations (nothing can be said about the odd subharmonic oscillating solutions), in the tilted case it guarantees the occurence of all subharmonic oscillations. Still some authors report the occurence of odd subharmonic oscillations in the vertical case, unlike the even oscillatory orbits, those are very rare and hard to find. In this work we show, through numeric simulations and experimental data, that in the tilted case they can be easily found in resonance regions, probably because their basins of attraction have different characteristics in both cases. The experimental data presented in this thesis were taken at the Laboratory of Nonlinear Phenomena (LFNL) at the Physics Institute of the University of São Paulo (IFUSP), in collaboration with Prof. Dr. José Carlos Sartorelli. To the Kepler problem, the inhomogeneities in the mass distribution of the heavy body generating the gravitational field are described through multipolar expansion. We know the dipole term keeps the integrability of the system. The quadrupole term, instead, can lead to the occurence of chaotic orbits in the system. In 2001, Géron and Letelier, based on numeric simulations, assert that the system is integrable if the perturbation is of oblate type, but chaotic if it is of prolate type. However, in a more recent work, Letelier et al show, also via numeric computation, that both cases can present chaotic trajectories. We solve this inconsistency in the literature by determining that the occurence of chaos in fact does not depend on the deformation type. Our results agree with the more general case studied in the literature / Doutorado / Física / Doutora em Ciências / 141762/2011-0 / CNPQ

The consequences of two key approximations of accretion-disc physics near black holes are studied in this thesis. First, the question of effective ``pseudo-Newtonian" potentials mimicking a black hole is investigated both through numerical simulations and analytical means, and second, the neglect of additional gravitating matter near accreted-upon black holes and its consequences are put to test. After some broader discussion of integrability, resonance and chaos, a general "pseudo-Newtonian" limit for geodesic motion is derived, and applied for the case of null geodesics near a glowing toroid and for time-like geodesics in the Kerr metric. Afterwards, a new Newtonian gravitational potential for non- singular toroids is proposed and its usefulness for the so-called Weyl space-times is discussed. Finally, a new pseudo-Newtonian potential is introduced and applied alongside already known potentials in models of free test particle motion in the field of a black hole with a disc or ring, in complete analogy with previous exact-relativistic studies, and the previous conclusion of chaos in disc/ring-hole models is confirmed. Overall, the pseudo-Newtonian framework is able to reproduce a number of key features of the original systems with notable differences arising only as a consequence of extremely strong or...