Orientador: Adriano A. Natale / Banca: Silvio Paolo Sorella / Banca: Arlene Cristina Aguilar / Resumo: O presente trabalho diz respeito ao vértice ghost-gluon da Cromodinâmica Quântica, o qual, de acordo com a identidade de Taylor, não possui correções perturbativas no calibre de Landau para uma determinada configuração de momentos. Estudamos este vértice numa configuração para a qual não há provas de um tal resultado, que é para o momento do gluon igual a zero. Para tanto, adotamos a abordagem da "Teoria Dinâmica de Perturbação", que consiste em inserir características não perturbativas da teoria em sua expansão perturbativa. Trata-se de uma tentativa de caráter fenomenológico apenas, que objetiva explorar propriedades da teoria no domínio infravermelho por meio de cálculos de loop. Utilizamos duas informações não perturbativas: Primeiramente, uma massa finita do gluon, visto que há consideráveis indicações de que ele apresente uma massa, embora esta seja o que se chama de dinâmica - ela, inerentemente, varia de um valor finito no infravermelho para zero no ultravioleta. Em segundo, um resultado recente acerca da carga efetiva da Cromodinâmica Quântica, na qual é considerada uma massa dinâmica do gluon. Calculamos então a correção, a 1 loop, do vértice ghost-gluon, com o fim de verificar o quão próxima a função de renormalização (~Z1) desse vértice é de 1. O resultado obtido foi positivo neste sentido: ~Z1 difere pouco de 1, como mostrado no Cap. 5. O resultado, ainda, é melhor ajustado aos dados da rede quando consideramos a referida carga efetiva, do que quando usamos a constante de acoplamento como um parâmetro de ajuste. Portanto, nossa abordagem um tanto fenomenológica, baseada numa massa dinâmica do gluon, é ao menos consistente e dá suporte à aproximação ~Z1 1, comumente efetuada no estudo das equações de Schwinger-Dyson da Cromodinâmica Quântica / Abstract: The present work concerns the ghost-gluon vertex of Quantum Chromodynamics, which, according to the Taylor identity, has no perturbative corrections to any order, in the Landau gauge and for a specific momentum configuration. We study this vertex for a momentum configuration for which there is no proof of such a result, which is the one with a zero gluon momentum. The framework we adopt for it is the "Dynamical Perturbation Theory" approach, which consists of inserting some nonperturbative information of the theory into its perturbative expansion. It is a phenomenological attempt only, intended to probe infrared properties of the theory by means of loop calculations. We have made use of two nonperturbative informations: First, a finite gluon mass, since there are even more indications that the gluon presents a mass, though it is a dynamical one - it intrinsically changes from finite in the infrared, to zero in the ultraviolet. Second, a recent result on the effective charge of Quantum Chromodynamics, which itself considers a dynamical gluon mass. We calculate the 1-loop correction to the ghost-gluon vertex, aiming at verifying how close to 1 the ghost-gluon vertex renormalization function (~Z1) is. The result obtained was positive in this direction: ~Z1 does not differ much from unity, as shown in Chap.5. Moreover, our result ts better the lattice data when we consider the mentioned effective charge, than when we set the coupling constant as a t parameter. Therefore, our somewhat phenomenological approach based on a dynamical gluon mass is, at least, consistent, and supports the approximation ~Z1 1, usually performed in the study of the Schwinger-Dyson equations of Quantum Chromodynamics / Mestre

This thesis uses a variety of numerical and statistical techniques to perform high precision calculations in high energy physics using quantum field theory. It introduces the experimental motivation for the calculation of B meson form factors and includes a discussion of previous work. It then describes the modern theoretical framework describing these phenomena, outlining quantum chromodynamics and electroweak theory, and then illustrating the procedure of gauge fixing, the quantum effective action and background field gauge which is required for subsequent perturbative work. Details of the basic methodology of lattice quantum field theory are given as well as the specific formulation of the relativistic theory and nonrelativistic approximations used in this work to describe quantum chromodynamics. A comprehensive calculation of the zero recoil B to D* form factor is then presented, using state of the art lattice techniques with relativistic charm sea quarks and light sea quarks with correct physical masses, leading to a discussion of the dominant sources of uncertainty and possible resolutions of experimental tensions. Also included is preliminary work towards the full calculation of nonzero recoil matrix elements, with the aim of outlining possible future work. Finally, this thesis presents the computation of parameters correcting for radiative one loop phenomena and corrections to the kinetic coupling parameters in nonrelativistic quantum chromodynamics in order to achieve a desirable level of precision in future calculations. This is done using Monte-Carlo integration to evaluate integrals from diagrams generated using automated lattice perturbation theory in background field gauge in order to match the coefficients of the effective action between the lattice and the continuum.

No presente trabalho, investigamos algumas propriedades da qcd quando incorporadas aos modelos efetivos. Mostramos que muitas propriedades da materia densa quente ou fria podem ser melhor descritas a partir do modelo quiral SIGMA-OMEGA. Mostramos que, em contraste com o modelo renormalizado de walecka, as correcoes de vacuo sao cruciais para uma adequada descricao da materia nuclear densa. Estes resultados tambem sao confirmados a partir das previsoes feitas para estrelas de neutrons. Um possivel sinal da transicao de fase em colisoes de ions pesados relativisticos e tambem calculado pela observacao das taxas de decaimento do pion nos canais PI POT.-SETAMU POT. -+NU IND.MU e PI POT.-SETAVARRHO POT.-+SETAVARRHO POT.-+NU IND.VARRHO. Mostramos que as propriedades de confinamento e liberdade assintotica, incorporadas pelo modelo de sacola do mit, dao suporte para a especulacao da possivel existencia de estrelas hibridas / In this work we investigate some properties of QCD as incorporated in effective models. We show that several properties of cold or hot and dense nuclear matter can be well described in the context of the chiral - model. We show that, in contrast to the nom chiral Walecka model vacuum renormalization corrections are crucial to provide for an adequate description. This result is also confirmed in the description of neutron stars. A possible signature of chiral phase transition in RHI collisions is also pointed out in the observation of the ratio of pion decay in the two channels POT. POT. + IND. and POT. e POT. + IND. e. We also show that the properties of confinement and asymptotic freedom as incorpored by the Bag model give support to the speculation on the existence of hybrid stars.

Bibliography: p. 156-162. Chronological list of the author's works: p. 155.

Bibliography: p. 156-162. / Chronological list of the author's works: p. 155. / viii, 162 p. : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 2002

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 112-116).

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (p. 125-160).

Not available / text

Copies of author's previously published articles inserted / Bibliography : leaves 171-190 / v, 190 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Physics and Mathematical Physics, 1991