Made available in DSpace on 2014-06-11T19:32:11Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-09-20Bitstream added on 2014-06-13T19:21:29Z : No. of bitstreams: 1 goncalves_es_dr_ift.pdf: 692007 bytes, checksum: 0e259499158fa0aa2c97c2ac489645b9 (MD5) / Dois tópicos importantes e atuais em teoria quântica de campos, a saber, Teorias com Derivadas de Ordem mais Alta e Determinação de Limites para a Massa do Fóton, são considerados. Como protótipos para as teorias de ordem mais alta selecionamos a Eletrodinâmica de Lee e Wick e a Gravitação Massiva em 3D. Ambas as teorias são de relevância especial para a física contemporânea. A primeira por constituir o alicerce sobre o qual o Modelo Padrão de Lee e Wickse assenta, enquanto que a outra é a única teoria de gravitação com derivadas de ordem mais alta conhecida até o momento cuja versão linearizada é unitária em nível de árvore. Novas e interessantes propriedades relativas às mencionadas teorias são estudadas em detalhe. Finalmente, limites clássicos e quânticos para a massa do fóton são estimados / Two important and current topics in quantum field theory, namely, Higher-Derivative Theories and Bounds on the Photon Mass, are considered. As prototypes for the higher-order theories we have singled out Lee-Wick Finite Electrodynamics and Massive Gravity in 3D. Both theories are of special relevance to contemporary physics. The former because it is the base on which the Lee-Wick Standard Model rests, while the other is the only higher-order gravity theory known up to now whose linearized version istree-levelunitary. Novel and interesting properties related to both theories area nalyzed in detail. Finally, classical and quantum bounds on the photon mass are estimated

Quantum field theory is studied within the semi-classical gravity approximation. The quantum correction to the propagation of both photons and gravitons in a general curved space background is calculated showing a non-trivial spacetime refractive index as well as a dynamical dressing (or undressing) of the particle state. The initial interacting particle's 'dressing', the cloud of virtual particles that surrounds it, may receive corrections from an infinite number of modes even for flat space. When gravitational tidal effects remove this dressing, squeezing it back into the bare particle, this leads to an amplification in a way consistent with unitarity. There is a possible shift discovered in the graviton wavefront velocity related to higher order curvature couplings, although in this calculation there is also a logarithmic divergence at high frequencies, leading to a breakdown of the perturbative approximation. Next we consider initial value problems and the stability of de Sitter space. Here the self decay of a massive scalar in de Sitter space is proposed to lead to a particle explosion where divergent growth of the field expectation value is observed. Directly investigating this divergent field expectation value a one loop calculation is completed for a massive scalar particle in 3-dimensional de Sitter space. This result has characteristic secular growth that can be summed into a rapidly decaying exponential by using the dynamical renormalisation group. Finally the evolution of two point functions is studied, by numerically solving their equations of motion using the Kaydanoff-Baym equations in 2-dimensional de Sitter space. Here we see a decay of the vacuum state due to the coupling. This appears to be related to the choice of initial conditions be chosen to match the free field vacuum plus non-interacting particles. This choice is made inappropriate by the dynamical dressing of the bare particle states.

Orientador: Bruto Max Pimentel Escobar / Coorientador: Rodolfo Alván Casana Sifuentes / Banca: Juan Carlos Montero Garcia / Banca: Ademir Eugênio de Santana / Banca: Celso Luiz Lima / Banca: Fernando Tadeu Caldeira Brandt / Resumo: Estudamos as propriedades termodinâmicas de algumas Teorias de Campo bidimensionais: os modelos de Schwinger, Thirring e Thirring com simetria de gauge (que chamaremos de Modelo de Kondo). O estudo é baseado na aplicação sistemática do formalismo de Dirac para tratar sistemas vinculados com o intuito de estabelecer a função de Partição via formalismo de integração / Abstract: We study the thermodynamical properties of some bidimensional Quantum Field Theories: the Schwinger model, Thirring model and the gauged Thirring model. The study is based on the systematic application of the Dirac's formalism for constrained systems with the intention of establishing the Partition function via the functional integration formalism / Doutor

Orientador: Antonio José Accioly / Banca: Henrique Boschi Filho / Banca: Humberto Belich Junior / Banca: Júlio Marny Hoff da Silva / Banca: Andrei Mikhailov / Resumo: Dois tópicos importantes e atuais em teoria quântica de campos, a saber, Teorias com Derivadas de Ordem mais Alta e Determinação de Limites para a Massa do Fóton, são considerados. Como protótipos para as teorias de ordem mais alta selecionamos a Eletrodinâmica de Lee e Wick e a Gravitação Massiva em 3D. Ambas as teorias são de relevância especial para a física contemporânea. A primeira por constituir o alicerce sobre o qual o Modelo Padrão de Lee e Wickse assenta, enquanto que a outra é a única teoria de gravitação com derivadas de ordem mais alta conhecida até o momento cuja versão linearizada é unitária em nível de árvore. Novas e interessantes propriedades relativas às mencionadas teorias são estudadas em detalhe. Finalmente, limites clássicos e quânticos para a massa do fóton são estimados / Abstract: Two important and current topics in quantum field theory, namely, Higher-Derivative Theories and Bounds on the Photon Mass, are considered. As prototypes for the higher-order theories we have singled out Lee-Wick Finite Electrodynamics and Massive Gravity in 3D. Both theories are of special relevance to contemporary physics. The former because it is the base on which the Lee-Wick Standard Model rests, while the other is the only higher-order gravity theory known up to now whose linearized version istree-levelunitary. Novel and interesting properties related to both theories area nalyzed in detail. Finally, classical and quantum bounds on the photon mass are estimated / Doutor

Orientador: George Emanuel Avraam Matsas / Banca: João Ramos Torres de Mello Neto / Banca: Daniel Augusto Turolla Vanzella / Resumo: A Teoria Quântica de Campos em Espaços Curvos fornece um arcabouço teórico consistente para o estudo de diversos fenômenos em que o caráter quântico dos campos e a curvatura clássica do espaço-tempo são importantes, mas em que a natureza quântica da gravitação nãoo exerce um papel relevante. Em particular, a emissão de radiação por uma fonte nas imediações de um buraco negro tem sido analisada, nesse contexto, com perspectivas diversas, dentre as quais está a busca de uma compreensão detalhada dos processos de emissão por discos de acreção e da influência da curvatura espaço-temporal sobre tais processos. De fato, a emissão de radiação por discos de acreção é uma das principais evidências observacionais da existência de buracos negros. Além da emissão térmica de bremsstrahlung devida a efeitos de colisões locais, o movimento global de cargas individuais ao redor do buraco negro também as faz irradiar, efeito por vezes chamado de radiação síncrotron gravitacional. Nesta dissertação, nós estendemos a análise da radiação devida a uma fonte, considerando um conjunto de fontes em rotação ao redor de um buraco negro. Discutimos a contribuição desse efeito para discos de acreção e investigamos os processos de interferência e como eles são modificados pela curvatura espaço-temporal / Abstract: Quantum Field Theory in Curved Spacetimes provides a theoretical framework for the investigation of phenomena in which the quantum nature of fields and the classicalspacetimecurvatureareimportantbutinwhichthequantumnatureofgravitation does not play a crucial role. In particular, radiation emission by a source in the vicinity of a black hole has been analyzed in this context with a number of motivations, one of which is to fully understand radiation emission processes by accretion discs and how they are modified by the nontrivial curvature of the black hole spacetime. In fact, radiation emission by accretion discs is one of the main observational evidences of the existence of black holes. Besides thermal bremsstrahlung emission due to local collision effects, the global motion of individual charges around a black hole also causes them to radiate; an effect often called gravitational synchrotron radiation. In this thesis, we extend the analysis of radiation due to one source by considering an ensemble of sources orbiting a black hole. We discuss the contribution of this effect to accretion discs, and investigate the interference processes that take place and how they are modified by space-time curvature / Mestre

Nesta tese, um estudo é feito do modelo bi-dimensional descrito pela densidade de Lagrangeana. Na primeira parte deste trabalho, discute- se a teoria de perturbação na constante de acoplamento g para as funções de Green. Mostra-se como e possível construir um esquema de renormalização de modo que não sejam induzidas interações quadri-lineares nos férmions quando M=0. Aplicando a identidade de Ward da corrente axial, prova-se então, que o limite M = 0 coincide, em qualquer ordem de g, com as funções de Green do modelo com massa do fermion nula, que e exatamente solúvel. Na segunda parte da tese , o termo de massa do férmion em L é tratado como uma perturbação em torno da teoria não livre. Após uma resomação parcial da série perturbativa, mostra-se que as funções de Green Euclidianas tornam-se finitas no intervalo O g POT. 2< pela introdução de um contra-termo proporcional a (:cos2g:1). A quebra da invariança pelas transformações - POT. 5 é verificada explicitamente por meio da identidade de Ward da corrente axial. / In this thesis, a study is made of the two-dimensional model described by the Lagrangean density. In the first part of this work, the perturbation theory in the coupling constant g is discussed for the Green functions. It is shown how to construct a renormalization scheme such that no four-linear interactions in the fermion field are induceded when m=0 by applying the axial current Ward identity, it is then proved that the M=O limit agrees, in every order of g, with the Green functions of the soluble model with massless fermion. In the second part of the thesis, the fermion mass term in L is considered as a perturbation on the interacting theory. After a partial resummation of the perturbative series, it is shown that the Euclidean Green functions are made finite for 0g²< introducing a counter-term proportional to (:cos2g:1). Breaking of -5 symmetry is explicity verified through the axial current Ward identity.

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The purpose of this thesis is to examine the gravitational scattering of massless scalar particles, photons, four component neutrinos, and two component neutrinos by one another. A modification of the quantum theory of the weak gravitational field developed by Gupta is used as a basis for the considerations. Cross-sections are given for the gravitational scattering of scalar particles by: scalar particles, photons, four component neutrinos, and two component neutrinos; of photons by: photons, four component neutrinos, and two component neutrinos; of four component neutrinos by four component neutrinos, and of two component neutrinos by two component neutrinos. The cross-section given by Barker et al and by Boccaletti et al for the scattering of photons by photons is confirmed. The cross-section for the scattering of massive scalar particles by massive scalar particles quoted by DeWitt and the cross-section for the scattering of photons by massive scalar particles given by Boccaletti et al are found to be in error and are corrected. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

In this thesis, we develop a perturbative formulation of non-equilibrium thermal quantum field theory, capable of describing the evolution of both temporal and spatial inhomogeneities in relativistic, quantum-statistical ensembles. We begin with a review of the necessary prerequisites from classical thermodynamics, classical and quantum statistical mechanics, quantum field theory and equilibrium thermal field theory. Setting general boundary conditions on the ensemble expectation values of products of interaction-picture creation and annihilation operators, we derive free propagators in which space-time translational invariance is explicitly broken. By means of the Schwinger-Kelydsh, closed-time path formalism, we are then able to introduce a path-integral description that accounts consistently for these temporal and spatial inhomogeneities. Subsequently, we develop a time-dependent perturbation theory that is free of the pathologies previously thought to spoil such approaches to non-equilibrium dynamics. Following an unambiguous definition of the number density of particles, we derive from first principles perturbative, field-theoretic evolution equations for statistical distribution functions. These evolution equations do not rely on the gradient expansion of so-called Wigner functions, as is necessary in the alternative Kadanoff-Baym approach, and are consistent with the well-known Boltzmann equations in the classical limit. Finally, with reference to a simple toy model, we highlight the appearance of processes otherwise kinematically disallowed in existing approaches to thermal field theory. These evanescent contributions are a consequence of the microscopic violation of energy conservation and are shown to be significant to the early-time evolution of non-equilibrium systems. We observe that the spectral evolution oscillates with time-dependent frequencies, which is interpreted as a signal of non-Markovian, memory effects.