Faddeev approach to confined three-quark problems

We propose a method that allows for the efficient solution of the three-body Faddeev equations in the presence of infinitely rising confinement interactions. Such a method is useful in calculations of nonrelativistic and especially semirelativistic constituent quark models. The convergence of the partial wave series is accelerated and possible spurious contributions in the Faddeev components are avoided. We demonstrate how the method works with the example of the Goldstone-boson-exchange chiral quark model for baryons.Comment: 6 page

Chiral symmetry restoration in excited hadrons, quantum fluctuations, and quasiclassics

In this paper, we discuss the transition to the semiclassical regime in excited hadrons, and consequently, the restoration of chiral symmetry for these states. We use a generalised Nambu-Jona-Lasinio model with the interaction between quarks in the form of the instantaneous Lorentz-vector confining potential. This model is known to provide spontaneous breaking of chiral symmetry in the vacuum via the standard selfenergy loops for valence quarks. It has been shown recently that the effective single-quark potential is of the Lorentz-scalar nature, for the low-lying hadrons, while, for the high-lying states, it becomes a pure Lorentz vector and hence the model exhibits the restoration of chiral symmetry. We demonstrate explicitly the quantum nature of chiral symmetry breaking, the absence of chiral symmetry breaking in the classical limit as well as the transition to the semiclassical regime for excited states, where the effect of chiral symmetry breaking becomes only a small correction to the classical contributions.Comment: RevTeX4, 20 pages, 4 Postscript figures, uses epsfig.sty, typos correcte

Parity Doubling in the Meson Spectrum

A simple argument for the restoration of parity symmetry high in the hadron spectrum is presented. The restoration scale is estimated to be 2.5 GeV. This in turn implies that typical quark model phenomenology such as scalar confinement or the $^3P_0$ decay model are only useful for low lying states. Minimal requirements for constructing more general phenomenologies are discussed. An additional mass degeneracy between $J^{++}$ and $J^{--}$ states is shown to occur and an isovector $3^{++}$ state is predicted at roughly 1700 MeV, in contradiction with the naive quark model. Similarly, isovector and isoscalar $4^{--}$ states are predicted at 2000 MeV. Finally, these results imply that Regge trajectories must become nonlinear at high spin.Comment: 5 pages, revtex, no figures, no tables. Version to appear in PL

The Nucleon-Nucleon Interaction in a Chiral Constituent Quark Model

We study the short-range nucleon-nucleon interaction in a chiral constituent quark model by diagonalizing a Hamiltonian comprising a linear confinement and a Goldstone boson exchange interaction between quarks. The six-quark harmonic oscillator basis contains up to two excitation quanta. We show that the highly dominant configuration is $\mid s^4p^2[42]_O [51]_{FS}>$ due to its specific flavour-spin symmetry. Using the Born-Oppenheimer approximation we find a strong effective repulsion at zero separation between nucleons in both $^3S_1$ and $^1S_0$ channels. The symmetry structure of the highly dominant configuration implies the existence of a node in the S-wave relative motion wave function at short distances. The amplitude of the oscillation of the wave function at short range will be however strongly suppressed. We discuss the mechanism leading to the effective short-range repulsion within the chiral constituent quark model as compared to that related with the one-gluon exchange interaction.Comment: 31 pages, LaTe

Electroweak properties of baryons in a covariant chiral quark model

The proton and neutron electromagnetic form factors and the nucleon axial form factor have been calculated in the Goldstone-boson exchange constituent-quark model within the point-form approach to relativistic quantum mechanics. The results, obtained without any adjustable parameter nor quark form factors, are, due to the dramatic effects of the boost required by the covariant treatment, in striking agreement with the data.Comment: Proceedings of the Conference N*2001, Mainz; 4 pages, 3 figures included in eps format; World Scientific style file include

Photocouplings of nucleon resonances with gluon and pion exchange currents

Photocouplings for the nucleon resonances most relevant to total photoabsorption are calculated in a constituent quark model including gluon and pion exchange. The sensitivity of the results to the different ingredients of the model is discussed.Comment: 23 pages including 9 tables, LaTe

Covariant axial form factor of the nucleon in a chiral constituent quark model

The axial form factor G_A of the nucleon is investigated for the Goldstone-boson-exchange constituent quark model using the point-form approach to relativistic quantum mechanics. The results, being covariant, show large contributions from relativistic boost effects. The predictions are obtained directly from the quark-model wave functions, without any further input such as vertex or constituent-quark form factors, and fall remarkably close to the available experimental data.Comment: 10 pages, 1 figure in .eps format, typeset with Elsevier elsart style files included. Revised version with a newly added section about discussion of results. To appear in Phys. Lett.

Nucleon electromagnetic and axial form factors in point-form relativistic quantum mechanics

Results for the proton and neutron electric and magnetic form factors as well as the nucleon axial form factor are presented for constituent quark models, based on either one-gluon-exchange and Goldstone-boson-exchange dynamics. The calculations are performed in a covariant framework using the point-form approach to relativistic quantum mechanics. The only input to the calculations is the nucleon wave function of the corresponding constituent quark model. A comparison is given to results of the instanton-induced constituent quark model treated with the Bethe-Salpeter equation.Comment: 4 pages, 6 figures, contribution to XVIII European Conference on Few-Body Problems in Physics, September 2002, Bled, Sloveni

Covariant electroweak nucleon form factors in a chiral constituent quark model

Results for the proton and neutron electric and magnetic form factors as well asthe nucleon axial and induced pseudoscalar form factors are presented for the chiral constituent quark model based on Goldstone-boson-exchange dynamics. The calculations are performed in a covariant framework using the point-form approach to relativistic quantum mechanics. The direct predictions of the model yield a remarkably consistent picture of the electroweak nucleon structure.Comment: 4 pages, 3 figures revte