Made available in DSpace on 2014-06-11T19:25:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2004-08Bitstream added on 2014-06-13T18:53:35Z : No. of bitstreams: 1 silva_arr_me_ift.pdf: 813157 bytes, checksum: 81b6685998a09d3d6718aaf28eb17b51 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / A proposta deste trabalho é investigar a validade da segunda lei generalizada da termodinâmica de buracos negros para um buraco negro de Schwarzschild por meio de experimentos mentais. Primeiramente, faremos uma breve revisão sobre termodinâmica de buracos negros. O conceito da segunda lei generalizada é estabelecido e os principais experimentos mentais são revistos. Em seguida, propomos um novo teste à segunda lei generalizada utilizando a mesma estratégia dos experimentos mentais. Veremos que a segunda lei generalizada é consistente com este novo teste. / The proposal of this work is to investigate the validity of the generalized second law of black hole thermodynamics for Schwarzschild black hole by means of gedankenexperiments. Firstly, we make a brief review about black hole thermo-dynamics. The notion of generalized second law is established and the essential gedankenexperiments are reviewed. Afterwards, we propose a new test for generalized second law using the same strategy of gedankenexperiments. We see that the generalized second law is consistent with this new test as well.

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All street hawkers are not the same in many Newly Industrialized Countries (NICs) of the global south as often portrayed by the media and documented in extant literature. This perception has created a gap in knowledge as researchers explore street hawking activities in NICs. In this study, I investigated a new informality trend of street hawking is coming into being within the capital city of Accra, Ghana. As governance is increasingly becoming entrepreneurial, informal activities are gradually becoming formal. Formal and registered businesses are increasingly capitalizing on hawking activities to occupy public spaces. The advent of the informality trend, I term corporate street hawking opens up new issues for the political economy, labor, and urban studies. By employing semi-structured interviews with 47 street hawkers in Accra, this paper sought to investigate three broadly interrelated questions. First, how do neoliberal policies impact the production of public space in Accra? Second, is corporate street hawking a form of creative destruction? Finally, how do corporate street hawkers practice agency within Accra?

L'effet Hawking prédit, dans un espace-temps décrivant l'effondrement d'une étoile à symétrie sphérique vers un trou noir de Schwarzschild, qu'un observateur statique, situé à l'infini, observera un flux thermal de particules quantiques à la température de Hawking. La première démonstration mathématique de l'effet Hawking pour des champs quantiques libres est due à Bachelot, dont le travail sur les champs de Klein-Gordon a été ensuite étendu aux champs de Dirac, d'abord par Bachelot lui-même, puis par Melnyk. Ces travaux, placés dans le cadre d'une symétrie sphérique, ont été complétés par Häfner, qui donna une démonstration rigoureuse de l'effet Hawking pour des champs de Dirac, autour d'une étoile s'effondrant vers un trou noir de Kerr. Le but de cette thèse est d'étudier l'effet Hawking non plus dans un modèle de champs quantiques libres, où les problèmes posés se ramènent à l'étude d'équations aux dérivées partielles linéaires, mais dans un modèle de champs de Dirac en interaction. L'interaction est supposée à support compact, statique, et localisée à l'extérieur de l'étoile. Nous choisissons de traiter le cas d'un modèle jouet, dans un espace-temps de dimension 1+1, situation à laquelle on peut se ramener, au moins dans le cas libre, en utilisant la symétrie sphérique du problème. Nous étudions le comportement de champs de fermions de Dirac dans différentes situations : d'abord, pour une observable suivant l'effondrement de l'étoile ; puis pour une observable stationnaire ; enfin, pour une interaction dépendante du temps, localisée près de la surface de l'étoile. Dans chacun de ces cas, nous montrons l'existence de l'effet Hawking et donnons l'état limite correspondant. / The Hawking effect predicts that, in a space- time describing the collapse of a spherically symmetric star to a Schwarzschild black hole, a static observer at infinity sees the Unruh state as a thermal state at Hawking temperature. The first mathematical proof of the Hawking effect, in the original setting of Hawking, is due to Bachelot. His work on Klein-Gordon fields has been extended to Dirac fields, in the first place by Bachelot himself, and by Melnyk after that. Those works, placed in the setup of a spherically symmetric star, have been completed by Häfner, who gave a rigorous proof of the Hawking effect for Dirac fields, outside a star collapsing to a Kerr black hole. The aim of this thesis is to study the Hawking effect not for a model of free quantum fields, in which case the problems can be reduced to studies on linear partial differential equations, but for a model of interacting Dirac fields. The interaction will be considered as a static, compactly-supported interaction, living outside the star. We choose to study a toy model in a 1+1 dimensional space-time. Using the fact that the problem is spherically symetric, one can, at least in the free case, reduce the real problem to this toy model. We study the behavior of Dirac fermions fields in various situations : first, for an observable following the star's collapse ; then, for a static observable ; finally, for a time-dependent interaction, fixed close to the star's boundary. In each of those cases, we show the existence of the Hawking Effect and give the corresponding limit state.

Dans cette thèse, nous étudions plusieurs aspects de la radiation de Hawking en présence de violations de l'invariance locale de Lorentz. Ces violations sont introduites par une modification de la relation de dispersion, devenant non-linéaire aux courtes longueurs d’onde. Les principales motivations de ces travaux ont une double origine. Il y a d’une part le développement en matière condensée de trous noirs analogues, ou l’écoulement d’un fluide est perçu comme une métrique d’espace-temps pour les ondes de perturbations et ou la radiation de Hawking pourrait être détectée expérimentalement. D’autre part, il se pourrait que des effets de gravité quantique puissent être modélisés par une modification de la relation de dispersion. En premier lieu, nous avons obtenu des caractérisations précises des conditions nécessaires au maintien de l’effet Hawking en présence de violation de l’invariance de Lorentz. De plus, nous avons étudié l’apparition d’une onde macroscopique de fréquence nulle, dans des écoulements de type trous blancs et également pour des champs massifs. Une autre partie de ce travail a consisté à analyser une instabilité engendrée par les effets dispersifs, ou la radiation de Hawking est auto-amplifiée, générant ainsi un flux sortant exponentiellement croissant dans le temps. / In this thesis, we study several features of Hawking radiation in the presence of ultraviolet Lorentz violations. These violations are implemented by a modified dispersion relation that becomes nonlinear at short wavelengths. The motivations of this work arise on the one hand from the developing field of analog gravity, where we aim at measuring the Hawking effect in fluid flows that mimic black hole space-times, and on the other hand from the possibility that quantum gravity effects might be approximately modeled by a modified dispersion relation. We develop several studies on various aspects of the prob- lem. First we obtain precise characterizations about the deviations from the Hawking result of black hole radiation, which are induced by dispersion. Second, we study the emergence, both in white hole flows or for massive fields, of a macroscopic standing wave, spontaneously produced from the Hawking effect, and known as ‘undulation’. Third, we describe in detail an instability named black hole laser, which arises in the presence of two horizons, where Hawking radiation is self-amplified and induces an exponentially growing in time emitted flux.

Orientador: Julio Marny Hoff da Silva / Resumo: Espinores exóticos surgem quando a topologia da variedade $M$ tomada como sendo o espaço-tempo é suposta ser não-trivial, no sentindo que seu grupo fundamental é não-trivial: $\pi_1(M) \neq 0$. Assim, um novo termo exótico $\partial_\mu \theta$ surge na equação dinâmica destes espinores, e novas propriedades se apresentam. A não-trivialidade de $\pi_1(M)$ pode ser diretamente ligada a própria existência de buracos negros. Assim, estudamos, nesta tese, relações entre estruturas espinoriais exóticas e a taxa de emissão de radiação Hawking por buracos negros assintoticamente \textit{flat} em Relatividade Geral, encontrando equações diferenciais para o termo exótico, o que dá a possibilidade de inferir uma forma explícita para $\theta$. Também, tratamos aqui dos chamados espinores RIM, que são espinores que respeitam uma equação dinâmica não-linear chamada de equação não-linear de Heisenberg. Apresentamos dois lemas relativos a estes espinores: um deles encontrando restrições para ocorrer a decomposição de espinores de Dirac em termos de espinores RIM, e outro que nega a existência de espinores RIM exóticos, ou seja, relaciona a existência de espinores RIM a própria estrutura topológica do espaço-tempo. Ainda, encontramos um método de classificarmos os espinores RIM nas classes de Lounesto. Por fim, apresentamos, na forma de dois teoremas, maneiras de deformar homotopicamente tais espinores no que chamamos de \textit{spinor-plane}. / Abstract: Exotic spinors emerge when the topology associatd to the manifold $M$, which is token as being the spacetime, is suppose to be non-trivial, in the sense that its fundamental group is non-trivial: $\pi_1(M) \neq 0$. Thus, a new exotic term $\partial_\mu \theta$ rises from the dynamical equation related to these spinors, and new properties are in order. The non-triviality of $\pi_1(M)$ may be directly linked to the very existence of black holes. In this vein, we study some relations between exotic spinorial structures and the Hawking radiation emission rate by asymptotically flat black holes solutions of General Relativity, finding an equation from which an explicity form for the exotic term could be inferred. Moreover, we work on the so-called RIM spinors, which are spinor fields satisfying a non-linear dynamical equation known as Heiseing non-linear equation. We present two \textit{lemmata} related to these spinors: one of them gives us restrictions for the decompostion of Dirac fields in terms of RIM spinors to occur, while the other deny the existence of exotic RIM spinors, i.e., it relates the very existence of RIM spinors to the spacetime topological structure. Besides, we develop a classifying method for RIM spinors into the Lounesto classes. Finally, we present, in the form of two theorems, ways to homotopically deform such spinors in what we call the spinor-plane. / Doutor

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-10-18T18:35:27Z No. of bitstreams: 1 LUIZ CORDEIRO DE LIMA NETO – DISSERTAÇÃO (PPGFísica) 2013.pdf: 963611 bytes, checksum: 83952da12a3c82dcd16e85616b111271 (MD5) / Made available in DSpace on 2018-10-18T18:35:27Z (GMT). No. of bitstreams: 1 LUIZ CORDEIRO DE LIMA NETO – DISSERTAÇÃO (PPGFísica) 2013.pdf: 963611 bytes, checksum: 83952da12a3c82dcd16e85616b111271 (MD5) Previous issue date: 2013-03-26 / Capes / Este trabalho apresenta elementos complementares da formação no nível de mestrado em Física. Discutimos, principalmente, aspectos de Relatividade Geral e Teoria Quân- tica de Campos. Deforma detalhada, explanamos a obtenção das soluções de Reissner- Nordström para as equações de Einstein que mostram a dependência dos buracos negros carregados da sua massa e da sua carga. Analisamos, também, os casos onde a massa difere numericamente da carga conhecidos como casos não-extremos, e os casos onde estas grandezas são equivalentes conhecidos como extremos. Discutimos, também, as leis da mecânica dos buracos negros e a inevitável comparação com as leis usuais da Termodinâmica e, conforme foi demonstrado por Hawking, que essas semelhanças são um fenômeno físico explicado pela a mecânica quântica. Ao rever estes estudos, Unruh percebeu que um observador acelerado em um espaço plano mede radiação térmica. Os estudos apresentados nesta dissertação constituem o embasamento necessário para o trabalho em inúmeras áreas de desenvolvimento da Física na atualidade, visto que os buracos negros carregados (em dimensões extras) possuem uma ligação com a teoria das cordas, uma das teorias mais promissoras para a construção da teoria quântica da gravitação. / This work presents complementary elements of training at the master’s degree level in Physics. We discussed, mainly, aspects of General Relativity and Quantum Field Theory. In details we expounded the obtaining of Reissner-Nordström’s solutions for Einstein’s equations that show the dependence of charged black holes on their massand charge. We also the cases in which the mass differs numerically from charge, known as non- extreme cases, and cases where the sequantities are equivalent, known as extreme. We also discuss the laws of mechanics of black holes and thein evitable comparison with the usual law softhermo dynamics and still, as demonstrated by Hawking, that the se similarities are physical phenomena explained by Quantum Mechanics. By reviewing thes estudies, Unruh realized that an accelerated observerina flat space me asures thermal radiation. The studies presented in this dissertation formed the necessary principles for research in several are as of development of physics now a days, where as the charged black holes (in extradimensions) are connected with the String Theory, one of the most promising theories for construction of the Quantum Theory of Gravitation.

Submitted by Emanuel Varela Cardoso (emanuel.varela@ufcg.edu.br) on 2018-10-09T18:55:52Z No. of bitstreams: 1 ARTHUR GONÇALVES CAVALCANTI – DISSERTAÇÃO (PPGFísica) 2016.pdf: 845402 bytes, checksum: dbdfb2a26834c477a45e9e735fa670d3 (MD5) / Made available in DSpace on 2018-10-09T18:55:52Z (GMT). No. of bitstreams: 1 ARTHUR GONÇALVES CAVALCANTI – DISSERTAÇÃO (PPGFísica) 2016.pdf: 845402 bytes, checksum: dbdfb2a26834c477a45e9e735fa670d3 (MD5) Previous issue date: 2016-02 / Capes / A teoria da relatividade geral prevê soluções tipo buraco negro, as quais são caracterizadas pela existência de um horizonte de eventos. Como exemplo, podemos citar a métrica obtida por Bãnados-Teitelboim-Zanelli (BTZ), que é uma solução da gravitação em (2+1)- dimensões, em que se considera uma constante cosmológica negativa. Nos últimos anos, buracos negros não-comutativos têm sido investigados na literatura por muitos autores. Em particular, a métrica BTZ não-comutativa foi obtida considerando-se a equivalência, que existe em três dimensões, entre gravitação e a teoria de Chern-Simons, que e uma teoria quântica de campos topológica em três dimensões, e usando-se o mapeamento de Seiberg-Witter com a solução em (2+1)-dimensões. A presença de divergências na teoria quântica de campos leva a considerar a possibilidade de modificar o princípio da incerteza de Heisemberg, introduzindo uma escala de comprimento fundamental, e esta modificação geram correções nas propriedades termodinâmica de buracos negros. Um dos efeitos associados as soluções tipo buraco negro, independente da dimensão do espaço-tempo, e a emissão térmica (Radiação Hawking), a qual e vista como um processo de tunelamento devido as flutuações do vácuo que acontece na região próxima ao horizonte de eventos. Neste trabalho, com o objetivo de investigar as correções devido a não comutatividade e ao princípio da incerteza generalizado, consideramos a métrica BTZ não-comutativa. Para tanto, usamos o formalismo de tunelamento via método de Hamilton-Jacobi. / The general relativity theory predicts black hole type solutions, which are characterized by the existence of an event horizon. As an example, the metric obtained by Ba~nados- Teitelboim-Zanelli (BTZ), which is a soluton of the gravitation in (2 + 1)-dimensions in what is considered a negative cosmological constant. In recent years, noncommutative black holes have been investigated by many authors in the literature. In particular, the BTZ metric non-commutative was obtained considering the equivalent, which exists in three dimensions, between gravitation and Chern-Simons theory, which is a quantum theory topological elds in three dimensions, and using it mapping Seiberg-Witter with the solution of (2 + 1)-dimensions. The presence of divergences in quantum eld theory leads to consider the possibility of modifying the principle of Heisenberg uncertainty by introducing a fundamental length scale, and this modi cation generate corrections to the thermodynamic properties of black holes. One of the e ects associated with the black hole type solutions, regardless of the space-time dimension is the thermal emission (Hawking radiation), which is seen as a process of tunneling due to vacuum uctuations that happens in the region near the event horizon . In this work, in order to investigate the corrections due to noncommutativity and the principle of widespread uncertainty, we consider the metric BTZ noncommutative. For this, we use tunneling formalism via Hamilton-Jacobi method.

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

Orientador: Prof. Dr. André Gustavo Scagliusi Landulfo / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Física, 2017. / Essa dissertação de mestrado tem por objetivos estudar e discutir as bases matemáticas e conceituais da teoria quântica de campos em espaços-tempos curvos (TQCEC) e analisar como podemos simular efeitos de TQCEC, como o efeito Hawking e o efeito Casimir dinâmico, usando circuitos supercondutores. Após o estudo do formalismo da relatividade geral e da TQCEC, é feita uma revisão sobre os modelos análogos de gravitação em fluidos. Em seguida analisamos a física dos chamados circuitos supercondutores e estudamos como achar análogos de efeitos de TQCEC usando tais sistemas. / This dissertation aims to study and discuss the mathematical and conceptual basis of quantum field theory in curved space-time (QFTCS) and analyse how we can simulate QFTCS effects, such as the Hawking effect and the dynamical Casimir effect, using superconducting circuits. After studying the general relativity formalism and QFTCS, a review is done on analogue models of gravitation in fluids. Then we analyse the physics of the so-called superconducting circuits and study how to find analogues of QFTCS effects using such systems.