Dissertações em Física (Mestrado) - PPGF/ICEN

URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/2340

O Mestrado Acadêmico iniciou-se em 2003 e pertence ao Programa de Pós-Graduação em Física (PPGF) do Instituto de Ciências Exatas e Naturais (ICEN) da Universidade Federal do Pará (UFPA).

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Navegando Dissertações em Física (Mestrado) - PPGF/ICEN por Orientadores "ALVES, Van Sérgio da Silva"

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    ItemAcesso aberto (Open Access)
    As funções do grupo de renormalização no modelo com auto-interação quártica fermiônica
    (Universidade Federal do Pará, 2009) NASCIMENTO, Leonardo Oliveira do; ALVES, Van Sérgio da Silva; http://lattes.cnpq.br/5346258049047843
    Four femion interactions models have been studied to clarify their conceptual aspects and possible applications in quantum field theory. In this work we present the structure of the renormalization group in the Nambu-Jona-Lasinio model up to 1-loop order. The model is not perturbatively renormalizable in the usual power counting sense, but it is treated as an effective theory, valid in a scale of energy where p <<^, being p the external moment of the loop and ^ a massive parameter that characterizes the coupling of the non-renormalizable vertex. We clarify the tensorial structure of the interaction vertices and calculate the functions of the renormalization group. The analysis of the fixed points of the theory is also presented using Zimmermann procedure for reducing the coupling constants. We find that the origin is an infrared-stable fixed point at low energies and has also a nontrivial ultraviolet stable fixed point, indicating that the theory could be perturbatively investigated if the momentum is low enough.
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    ItemAcesso aberto (Open Access)
    Quebra dinâmica da simetria quiral na pseudo eletrodinâmica quântica em (2 + 1) dimensões
    (Universidade Federal do Pará, 2011) ELIAS, Walace de Sousa; ALVES, Van Sérgio da Silva; http://lattes.cnpq.br/5346258049047843
    In the present work, we study the chiral symmetry breaking in pseudo quantum electrodynamics in (2+1) dimensions using the Schwinger-Dyson equation formalism and investigate the similarities of this model with the criticality in both QED3 and QED4. Using the rainbow-quenched approximation we show that there is a critical coupling αcc = π/16 above which there is a mass generation for fermions and hence the chiral symmetry breaking occurs. We also study the N massless fermions flavors version using the 1/N expansion in rainbow-unquenched approximation and we obtain a critical value for the number of active fermions below which there is chiral symmetry breaking. We show that at strong gauge coupling constant (g -- ∞) this critical number is the same as in QED3 in large N expansion.
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