Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 2002? / Bibliography: p. 377-382.

Thesis (Ph. D.)--Florida State University, 2004. / Advisor: Dr. Bernd A. Berg, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed June 16, 2004). Includes bibliographical references.

No description available.

Thesis (Ph.D.)--Duke University, 2009.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains x, 94 p.; also includes graphics Includes bibliographical references (p. 52-54). Available online via OhioLINK's ETD Center

No description available.

Thesis (Ph. D.)--University of Washington, 2004. / Vita. Includes bibliographical references (p. 119-135).

Lattice gauge theory is a special regularization of continuum gauge theories and the numerical simulation of lattice quantum chromodynamics (QCD) remains as the only first principle method to study non-perturbative QCD at low energy. The lattice spacing a, which serves as the ultraviolet cut off, plays a significant role in determining error on any lattice simulation results. Physical results come from extrapolating a series of simulations with different values for a to a=0. Reducing the size of these errors for non-zero a improves the extrapolation and minimizes the error. In the strong coupling limit the coarse lattice spacing pushes the analysis of the finite lattice spacing error to its limit. Section 4 measures two renormalized physical observables, the neutral kaon mixing parameter BK and the Delta I=3/2 K pi pi decay amplitude A2 on a lattice with coarse lattice spacing of a ~ 1GeV and explores the a^2 scaling properties at this scale. In the weak coupling limit the lattice simulations suffer from critical slowing down where for the Monte Carlo Markov evolution the cost of generating decorrelated samples increases significantly as the lattice spacing decreases, which makes reliable error analysis on the results expensive. Among the observables the topological charge of the configurations appears to have the longest integrated autocorrelation time. Based on a previous work where a diffusion model is proposed to describe the evolution of the topological charge, section 2 extends this model to lattices with dynamical fermions using a new numerical method that captures the behavior for different Fourier modes. Section 3 describes our effort to find a practical renormalization group transformation to transform lattice QCD between two different scales, whose knowledge could ultimately leads to a multi-scale evolution algorithm that solves the problem of critical slowing down. For a particular choice of action, we have found that doubling the lattice spacing of a fine lattice yields observables that agree at the few precent level with direct simulations on the coarser lattice. Section 5 aims at speeding up the lattice simulations in the weak coupling limit from the numerical method and hardware perspective. It proposes a preconditioner for solving the Dirac equation targeting the ensemble generation phase and details its implementation on currently the fastest supercomputer in the world.

Diese Arbeit befasst sich mit Quantenfeldtheorien auf nicht-kommutativen Räumen. Solche Modelle treten im Zusammenhang mit der Stringtheorie und mit der Quantengravitation auf. Ihre nicht-störungstheoretische Behandlung ist üblicherweise schwierig. Hier untersuchen wir jedoch drei nicht-kommutative Quantenfeldtheorien nicht-perturbativ, indem wir die Wirkungsfunktionale in eine äquivalente Matrixformulierung übersetzen. In der Matrixdarstellung kann die jeweilige Theorie dann numerisch behandelt werden. Als erstes betrachten wir ein regularisiertes skalares Modell auf der nicht-kommutativen Ebene und untersuchen den Kontinuumslimes bei festgehaltener Nicht-Kommutativität. Dies wird auch als Doppelskalierungslimes bezeichnet. Insbesondere untersuchen wir das Verhalten der gestreiften Phase. Wir finden keinerlei Hinweise auf die Existenz dieser Phase im Doppelskalierungslimes. Im Anschluss daran betrachten wir eine vier-dimensionale U(1) Eichtheorie. Hierbei sind zwei der räumlichen Richtungen nicht-kommutativ. Wir untersuchen sowohl die Phasenstruktur als auch den Doppelskalierungslimes. Es stellt sich heraus, dass neben den Phasen starker und schwacher Kopplung eine weitere Phase existiert, die gebrochene Phase. Dann bestätigen wir die Existenz eines endlichen Doppelskalierungslimes, und damit die Renormierbarkeit der Theorie. Weiterhin untersuchen wir die Dispersionsrelation des Photons. In der Phase mit schwacher Kopplung stimmen unsere Ergebnisse mit störungstheoretischen Berechnungen überein, die eine Infrarot-Instabilität vorhersagen. Andererseits finden wir in der gebrochenen Phase die Dispersionsrelation, die einem masselosen Teilchen entspricht. Als dritte Theorie betrachten wir ein einfaches, in seiner Kontinuumsform supersymmetrisches Modell, welches auf der "Fuzzy Sphere" formuliert wird. Hier wechselwirken neutrale skalare Bosonen mit Majorana-Fermionen. Wir untersuchen die Phasenstruktur dieses Modells, wobei wir drei unterschiedliche Phasen finden. / This work deals with three quantum field theories on spaces with noncommuting position operators. Noncommutative models occur in the study of string theories and quantum gravity. They usually elude treatment beyond the perturbative level. Due to the technique of dimensional reduction, however, we are able to investigate these theories nonperturbatively. This entails translating the action functionals into a matrix language, which is suitable for numerical simulations. First we explore a scalar model on a noncommutative plane. We investigate the continuum limit at fixed noncommutativity, which is known as the double scaling limit. Here we focus especially on the fate of the striped phase, a phase peculiar to the noncommutative version of the regularized scalar model. We find no evidence for its existence in the double scaling limit. Next we examine the U(1) gauge theory on a four-dimensional spacetime, where two spatial directions are noncommutative. We examine the phase structure and find a new phase with a spontaneously broken translation symmetry. In addition we demonstrate the existence of a finite double scaling limit which confirms the renormalizability of the theory. Furthermore we investigate the dispersion relation of the photon. In the weak coupling phase our results are consistent with an infrared instability predicted by perturbation theory. If the translational symmetry is broken, however, we find a dispersion relation corresponding to a massless particle. Finally, we investigate a supersymmetric theory on the fuzzy sphere, which features scalar neutral bosons and Majorana fermions. The supersymmetry is exact in the limit of infinitely large matrices. We investigate the phase structure of the model and find three distinct phases. Summarizing, we study noncommutative field theories beyond perturbation theory. Moreover, we simulate a supersymmetric theory on the fuzzy sphere, which might provide an alternative to attempted lattice formulations.

Neste trabalho estudamos as teorias de gauge puras (sem campo de matéria) na rede em três dimensões. Em especial, estudamos a subclasse das teorias topológicas. A maneira como denimos e tratamos as teorias de gauge e diferente, mas equivalente, à forma usual apresentada em [2, 3]. Definimos estas teorias via o formalismo de Kuperberg, que é um formalismo puramente matemático de um invariante topológico de variedades tridimensionais. Este formalismo, embora bastante abstrato, pode ser adaptado para descrever as classes de modelos das teorias de gauge na rede, e traz várias vantagens, pois possibilita que tratemos de teorias topológicas e não topológicas, além da fácil identicação dos limites topológicos da função de partição. Estudamos também a classe das teorias chamadas quase topológicas, que podem ser pensadas como deformações de teorias topológicas. Em particular, consideramos teorias de gauge com grupo de gauge Z2, que é o grupo de gauge mais simples possível com dinâmica não trivial. Dentro das teorias de gauge, identicamos as classes de modelos que são quase topológicos, além de outras classes nas quais a função de partição pode ser trivialmente calculada. A função de partição foi calculada explicitamente no caso quase topológico em duas situações: sobre a esfera tridimensional S3 e sobre o toroS1x S1x S1x, que representa uma rede com condições periódicas de contorno. Dois modelos físicos de teorias de gauge, ainda com grupo de gauge Z2, foram estudados: o modelo com ação de Wilson SW = Pfaces [Tr(g) - 1] e o modelo com ação spin-gauge SSG = Pfaces Tr(g). No limite de baixa temperatura ambos os modelos mostram-se ser topológicos, enquanto que no limite de alta temperatura mostraram-se ser trivialmente calculáveis. / In this work we studied the class of models of pure lattice gauge theories (without matter elds) in three dimensions. Especially, we studied the subclass of topological theories. Lattice gauge theories were dened in an unusual way, unlike the description shown in [2, 3]. We dened lattice gauge theories via the Kuperberg\'s formalism [4], which is a mathematical model for a topological invariant of 3-manifolds. Such formalism, although completely abstract, can describe the class of models of lattice gauge theories because it can describe both topological and non topological theories, besides it provides an easy identication of the partition function topological limits. We also studied the class of theories called quasi topological, which can be thought as deformations of topological theories. As an example, we consider Z2 as gauge group, because it is the simplest group that does not imply trivial dynamics. Inside this class of models we identify the subclasses of quasi topological theories and also other classes in which the partition function can be trivially computed. The partition function was explicitly computed in two situations: on the 3-sphere S3 and on the 3-manifold S1 x S1 x S1 that represents periodic boundary conditions. Two physical models were studied: the model with Wilson\'s action SW(conf)1 and the model with spin-gauge action SSG(conf)2. In the low temperature limit both models shown to be topological and in the high temperature limit they could be trivially computed.