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Made available in DSpace on 2014-06-11T19:25:30Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-02Bitstream added on 2014-06-13T20:53:28Z : No. of bitstreams: 1 talarico_maa_me_ift.pdf: 361026 bytes, checksum: 5a730dc52636ee298931463d66501029 (MD5) / Utilizamos o Método de Coordenadas Geradoras (MCG), o qual incorpora correlações de nosso interesse para a função de onda do núcleo de 'INTPOT. 4 HE', para o cálculo da densidade espacial e da distribuição de momentos. Inicialmente descrevemos o ansatz do MCG e apontamos os bem conhecidos problemas de instabilidade da função peso, solução de equação de Griffin-Wheeler; também apontamos como eles podem ser contornados com o procedimento de Piza e Passos. Desenvolvemos o método usando a interação nucleon-nucleon efetiva fenomenológica de Skyrme, a interação coulombiana e extraíndo o centro de massa do sistema. Finalmente os resultados são comparados com dados experimentais. Observa-se uma melhor descrição dos resultados na região de altos momentos transferidos / We use the Generator Coordinate Method (CGM), which take into account suitable correlations in the wave function of 'INTPOT. 4 HE' nuclei, to calculate the momentum distribution and spatial density. Firstly we describe the anzatz of the method and the well-known instability problems of the weight function, which is the solution of Griffin-Wheeler, furthermore we point out how they can be avoided with the use of the procedure proposed by Piza and Passos. We develop the method using the nucleon-nucleon fenomenological effective Skyrme interaction, Coulombian interaction and by extracting the center of mass of the sistem. Finally the results are compared with experimental data. We verify a better agreement of the results at the region of high transferred momenta

Made available in DSpace on 2014-06-11T19:32:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2002-02Bitstream added on 2014-06-13T19:21:26Z : No. of bitstreams: 1 schmidt_agm_dr_ift.pdf: 423945 bytes, checksum: 7e72cb55ad496a8b66eca34baf5a8469 (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Com a técnica da integração em dimensão negativa (NDIM) estudamos integrais de Feynman em calibres covariantes e não-covariantes, o do cone-de-luz e o de Coulomb. No primeiro caso, calculamos várias integrais ao nível de dois loops com e sem massa, e com momentos externos tanto na camada de massa quanto fora dela. Em calibres não-covariantes mostramos que podemos descartar a utilização de prescrições de calibre do cone-de-luz e mesmo assim obter resultados fisicamente compatíveis (que preservam a causalidade); no calibre de Coulomb integrais ao nível de um e dois loops podem ser facilmente resolvidas integrando em dimensão negativa, mas com dois parâmetros para as regularizar dimensionalmente / Abstracts: Using negative dimensional integration method (NDIM) we study several Feynman loop integrals pertaining to covariant and non-covariant gauges. In the first case we solve scalar integrals at two-loop level internal particles are massive or massless and external ones are even on or off-shell. Non-covariant gauges studied in this work are light-cone and Coulomb ones. We show that prescriptions, as well as any other devices such as partial fractioning and integration over components which are part of them, can be abandoned in the light-cone gauge, since NDIM can give us causality preserving results without invoking any of such prescriptions (Mandelstam-Leibbrandt for instance). In Coulomb gauge we also consider one and two-loop integrals in the context of split dimensional regularization