Pion Form Factor in the Light-Front

The pion electromagnetic form factor is calculated with a light-front quark model. The "plus" and "minus" component of the electromagnetic current are used to calculate the electromagnetic form factor in the Breit frame with two models for the q\bar{q} vertex. The light front constituent quark models describes very well hadronic wave function for pseudo-scalar and vector particles. Symmetry problems arinsing in the light-front approach are solved by the pole dislocation method. The results are compared with new experimental data and with other quark models.Comment: 4 pages,1 figure (eps), Latex,AIP style.To appear in the proceedings "IX Hadron Physics and VII Relativistic Aspects of Nuclear Physics: A Joint Meeting on QCD and QGP, Hadron Physics-RANP,2004,Angra dos Reis, Rio de Janeiro,Brazil.(some references are added and small mistakes are corrected.

Spin-1 Particle in the Light-Front Approach

The electromagnetic current of spin-1 composite particles does not transform properly under rotations if only the valence contribution is considered in the light-front model. In particular, the plus component of the current, evaluated only for the valence component of the wave function, in the Drell-Yan frame violates rotational symmetry, which does not allow a unique calculation of the electromagnetic form-factors. The prescription suggested by Grach and Kondratyuk [Sov. J. Nucl. Phys. 38, 198 (1984)] to extract the form factors from the plus component of the current, eliminates contributions from pair diagrams or zero modes, which if not evaluated properly cause the violation of the rotational symmetry. We address this problem in an analytical and covariant model of a spin-1 composite particle.Comment: To appear Brazilian Journal of Physics (2004), 4 pages, no figures. Use multicols.st

Experimental and numerical analysis of the cyclic behaviour of RC beam-column connections with plain reinforcing bars

The information available in the literature about the cyclic behaviour of reinforced concrete elements with plain reinforcing bars is scarce. As a consequence, the influence of bar slippage in elements with plain bars is not yet comprehensively understood. In this paper are presented and discussed the main results of the cyclic tests carried out on five full-scale reinforced concrete beam-column joints with plain bars and without specific detailing for seismic demands. An additional joint specimen with deformed bars was also tested for comparison. Furthermore, numerical models were built to simulate the response of two of the specimens. Particular attention was given to the influence of bar slippage. The results of the conducted analyses underline the importance of accounting for bond-slip in the numerical modelling of elements with plain bars and also highlight the need for specific models to simulate the effects of this mechanism in the presence of plain bars

Light-Front projection of spin-1 electromagnetic current and zero-modes

The issue of the contribution of zero-modes to the light-front projection of the electromagnetic current of phenomenological models of vector particles vertices is addressed in the Drell-Yan frame. Our analytical model of the Bethe-Salpeter amplitude of a spin-1 fermion-antifermion composite state gives a physically motivated light-front wave function symmetric by the exchange of the fermion and antifermion, as in the $\rho$-meson case. We found that among the four independent matrix elements of the plus component in the light-front helicity basis only the $0\to 0$ one carries zero mode contributions. Our derivation generalizes to symmetric models, important for applications, the above conclusion found for a simplified non-symmetrical form of the spin-1 Bethe-Salpeter amplitude with photon-fermion point-like coupling and also for a smeared fermion-photon vertex model.Comment: Use elservier style. 14 page

In-Medium Pion Valence Distribution Amplitude

After a brief review of the quark-based model for nuclear matter, and some pion properties in medium presented in our previous works, we report new results for the pion valence wave function as well as the valence distribution amplitude in medium, which are presented in our recent article. We find that both the in-medium pion valence distribution and the in-medium pion valence wave function, are substantially modified at normal nuclear matter density, due to the reduction in the pion decay constant.Comment: 9 pages, 10 figures, one paragraph added, typos corrected, to be published in the proceedings of "Light Cone 2016", September 5-8, 2016, Lisbon, Portuga

Superfluid and Fermi liquid phases of Bose-Fermi mixtures in optical lattices

We describe interacting mixtures of ultracold bosonic and fermionic atoms in harmonically confined optical lattices. For a suitable choice of parameters we study the emergence of superfluid and Fermi liquid (non-insulating) regions out of Bose-Mott and Fermi-band insulators, due to finite Boson and Fermion hopping. We obtain the shell structure for the system and show that angular momentum can be transferred to the non-insulating regions from Laguerre-Gaussian beams, which combined with Bragg spectroscopy can reveal all superfluid and Fermi liquid shells.Comment: 4 pages, 2 figure