Galactic Nonlinear Dynamic Model

We develop a model for spiral galaxies based on a nonlinear realization of the Newtonian dynamics starting from the momentum and mass conservations in the phase space. The radial solution exhibits a rotation curve in qualitative accordance with the observational data.Comment: 6 pages, 1 figure. Talk given in the 7th Alexander Friedmann International Seminar, June 29 to July 5, 2008, Joao Pessoa, PB, Brazi

Why pair production cures covariance in the light-front?

We show that the light-front vaccum is not trivial, and the Fock space for positive energy quanta solutions is not complete. As an example of this non triviality we have calculated the electromagnetic current for scalar bosons in the background field method were the covariance is restored through considering the complete Fock space of solutions. We also show thus that the method of "dislocating the integration pole" is nothing more than a particular case of this, so that such an "ad hoc" prescription can be dispensed altogether if we deal with the whole Fock space. In this work we construct the electromagnetic current operator for a system composed of two free bosons. The technique employed to deduce these operators is through the definition of global propagators in the light front when a background electromagnetic field acts on one of the particles.Comment: 11 pages, 2 figure

Electromagnetic structure and weak decay of pseudoscalar mesons in a light-front QCD-inspired model

We study the scaling of the $^3S_1-^1S_0$ meson mass splitting and the pseudoscalar weak decay constants with the mass of the meson, as seen in the available experimental data. We use an effective light-front QCD-inspired dynamical model regulated at short-distances to describe the valence component of the pseudoscalar mesons. The experimentally known values of the mass splittings, decay constants (from global lattice-QCD averages) and the pion charge form factor up to 4 [GeV/c]$^2$ are reasonably described by the modelComment: 27 Pages, 7 eps figures,use revtex

Relativistic Quark Spin Coupling Effects in the Nucleon Electromagnetic Form Factors

We investigate the effect of different forms of relativistic spin coupling of constituent quarks in the nucleon electromagnetic form factors. The four-dimensional integrations in the two-loop Feynman diagram are reduced to the null-plane, such that the light-front wave function is introduced in the computation of the form factors. The neutron charge form factor is very sensitive to different choices of spin coupling schemes, once its magnetic moment is fitted to the experimental value. The scalar coupling between two quarks is preferred by the neutron data, when a reasonable fit of the proton magnetic momentum is found.Comment: 13 pages, needs axodraw.ps and axodraw.sty for diagrams of Fig.

Weak decay constant of pseudscalar meson in a QCD-inspired model

We show that a linear scaling between the weak decay constants of pseudoscalar and the vector mesons masses is supported by the available experimental data. The decay constant scale as $f_m/f_{pi}=M_V/M_{\rho}$ (f_m is decay constant and M_V vector meson ground state mass). This simple form is justified within a renormalized light-front QCD-inpired model for quark-antiquark bound states.Comment: 4 pages, use revtex style. To appear "Brazilian Journal of Physics (2003)

Desenvolvimento de uma metodologia baseada na técnica fotoacústica para determinar porosidades em membranas vítreas porosas.

Este trabalho trata do desenvolvimento de um método fotoacústico para a determinação da porosidade de membranas vítreas, as quais são utilizadas como meios filtrantes. As membranas foram produzidas com diferentes porcentagens de poros: 10%, 20%, 30% e 40%, através da técnica de preenchimento. Após a sinterização das membranas, dois diferentes processos independentes foram realizados para a eliminação do material inerte e uniformização da espessura: i) membranas primeiro lavadas e depois lixadas; ii) membranas primeiro lixadas e depois lavadas. As medidas fotoacústicas das membranas com diferentes porosidades foram obtidas nas condições de varredura de freqüência de modulação de 12 a 500 Hz e utilizando-se a luz branca. O desenvolvimento da metodologia consiste em utilizar dois tipos de suporte de amostra, um denominado por "branco" e outro por "preto", para as medidas fotoacústicas. Para cada amostra nos suportes citados, as amplitudes dos sinais fotoacústicos foram diferentes durante a varredura de freqüência de modulação da luz. Estas amplitudes foram relacionadas entre si e normalizadas pela massa da membrana. Todo este procedimento foi aplicado a todas as membranas, possibilitando a distinção entre aquelas de diferentes porosidades.bitstream/CNPDIA/8124/1/BPD01_2002.pd