Strong Decays of N and Delta Resonances in the Point-Form Formalism

We present covariant predictions of relativistic constituent quark models for pi and eta decay widths of N and Delta resonances. The results are calculated for a model decay operator within the point-form spectator approximation. It is found that most theoretical values underestimate the experimental data considerably.Comment: 4 pages; Proceedings for N*2004, Grenoble, March 24-27 (2004

Nucleon magnetic moments in an extended chiral constituent quark model

We present results for the nucleon magnetic moments in the context of an extended chiral constituent quark model based on the mechanism of the Goldstone boson exchange, as suggested by the spontaneous breaking of chiral symmetry in QCD. The electromagnetic charge-current operator is consistently deduced from the model Hamiltonian, which includes all force components for the pseudoscalar, vector and scalar meson exchanges. Thus, the continuity equation is satisfied for each piece of the interaction, avoiding the introduction of any further parameter. A good agreement with experimental values is found. The role of isoscalar two-body operators, not constrained by the continuity equation, is also investigated.Comment: 7 pages, 1 table, submitted for publication to Phys. Lett. B, elsart.sty/elsart12.sty include

Hadronic Decays of N and \Delta Resonances in a Chiral Quark Model

\pi and \eta decay modes of light baryon resonances are investigated within a chiral quark model whose hyperfine interaction is based on Goldstone-boson exchange. For the decay mechanism a modified version of the 3P0 model is employed. Our primary aim is to provide a further test of the recently proposed Goldstone-boson-exchange constituent quark model. We compare the predictions for \pi and \eta decay widths with experiment and also with results from a traditional one-gluon-exchange constituent quark model. The differences between nonrelativistic and semirelativistic versions of the constituent quark models are outlined. We also discuss the sensitivity of the results on the parametrization of the meson wave function entering the 3P0 model.Comment: 17 pages, 6 eps figure

Chiral symmetry patterns of excited mesons with the Coulomb-like linear confinement

The spectrum of $\bar q q$ mesons in a model where the only interaction is a linear Coulomb-like instantaneous confining potential is studied. The single-quark Green function as well as the dynamical chiral symmetry breaking are obtained from the Schwinger-Dyson (gap) equation. Given the dressed quark propagator, a complete spectrum of "usual" mesons is obtained from the Bethe-Salpeter equation. The spectrum exhibits restoration of chiral and $U(1)_A$ symmetries at large spins and/or radial excitations. This property is demonstrated both analytically and numerically. At large spins and/or radial excitations higher degree of degeneracy is observed, namely all states with the given spin fall into reducible representations $[(0,1/2) \oplus (1/2,0)] \times [(0,1/2) \oplus (1/2,0)]$ that combine all possible chiral multiplets with the given $J$ and $n$. The structure of the meson wave functions as well as the form of the angular and radial Regge trajectories are investigated.Comment: 1. Order of references has been changed and one reference has been added; 2. A short discussion of nonrelativistic and semirelativistic quark models has been added in the conclusion part on referee's request. To appear in Phys. Rev.