Θ+\Theta^+ in a chiral constituent quark model and its interpolating fields

The recently discovered pentaquark $\Theta^+$ is described within the chiral constituent quark model. Within this picture the flavor-spin interaction between valence quarks inverts the $(1s)^4$ and $(1s)^3(1p)$ levels of the four-quark subsystem and consequently the lowest-lying pentaquark is a positive parity, I=0, J=1/2 state of the flavor antidecuplet, similar to the soliton model prediction. Contrary to the soliton model, however, the quark picture predicts its spin-orbit partner with $J=3/2$. Different interpolating fields intended for lattice calculations of $\Theta^+$ are constructed, which have a maximal overlap with this baryon if it is indeed a quark excitation in the 5Q system.Comment: 9 p

Extended Goldstone-Boson-Exchange Constituent Quark Model

We present an extension of the Goldstone-boson-exchange constituent quark model including additional interactions beyond the ones used hitherto. For the hyperfine interaction between the constituent quarks we assume pseudoscalar, vector, and scalar meson exchanges and consider all relevant force components produced by these types of exchanges. The resulting model, which corresponds to a relativistic Poincare-invariant Hamiltonian (or equivalently mass operator), provides a unified framework for a covariant description of all light and strange baryons. The ground states and resonances up to an excitation energy of about 2 GeV are reproduced in fair agreement with phenomenology, with the exception of the first excitations above the Lambda and Xi ground states.Comment: 11 pages, 4 figures, 3 tables; substantial revisions, additional author, bibliography extended and update

Local Current Operators for Arbitrary Spin Particles

Free current operators are constructed for massive particles with arbitrary spin $j$. Such current operators are related to representations of the U(N,N) type groups and are covariant under the (extended) Poincar\'{e} group and charge conjugation, where the charge conjugation operation is defined as an automorphism on U(N,N) elements. The currents are also required to satisfy current conservation, hermiticity, and locality. The condition that the currents be local is shown to be equivalent to certain integral constraints on form factors. These constraints are satisfied by writing the currents in terms of free local spin $j$ fields. It is shown that there are $(2j+1)$ different local currents for a spin $j$ particle, each with an arbitrary form factor, generalizing the Dirac and Pauli currents for spin 1/2 particles. Static properties of the various currents are also given.Comment: 25 page

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