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

Superfluid and insulating phases of fermion mixtures in optical lattices

The ground state phase diagram of fermion mixtures in optical lattices is analyzed as a function of interaction strength, fermion filling factor and tunneling parameters. In addition to standard superfluid, phase-separated or coexisting superfluid/excess-fermion phases found in homogeneous or harmonically trapped systems, fermions in optical lattices have several insulating phases, including a molecular Bose-Mott insulator (BMI), a Fermi-Pauli (band) insulator (FPI), a phase-separated BMI/FPI mixture or a Bose-Fermi checkerboard (BFC). The molecular BMI phase is the fermion mixture counterpart of the atomic BMI found in atomic Bose systems, the BFC or BMI/FPI phases exist in Bose-Fermi mixtures, and lastly the FPI phase is particular to the Fermi nature of the constituent atoms of the mixture.Comment: 4 pages with 3 figures (Published version