Quark model description of hadrons

In this contribution I will try to give an overview of what has been achieved in constituent quark models of mesons and baryons by a comparison of some selected results from various ansaetze with experimental data. In particular I will address the role of relativistic covariance, the nature of the effective quark forces, the status of results on electromagnetic and strong-decay observables beyond the mere mass spectra, as well as some unresolved issues in hadron spectroscopy.Comment: 10 pages, 5 figures. Plenary talk at Hadron 03: 10th International Conference on Hadron Spectroscopy, Aschaffenburg, Germany, 31 Aug - 6 Sep 200

Parity Doublets from a Relativistic Quark Model

The Nucleon- and the Lambda-excitation spectrum exhibit parity doublets, i.e. states of the same spin but with opposite parity being almost degenerate in mass. It is shown that in a relativistic quark model with instantaneous interaction kernels, where confinement is implemented by a linearly rising potential and the major mass splittings are generated from an interaction based on instanton effects, this degeneracy occurs quite naturally: Once the parameters of the instanton induced interaction are fixed to reproduce the ground state octet-decuplet splittings, some states are selectively lowered to a position which is degenerate with states of opposite parity. Some observable consequences are briefly discussed.Comment: 4 pages postscript including 3 figures, Proceedings of "Workshop on the Physics of Excited Nucleons" (NSTAR 2001), Mainz, Germany, 7-10 Mar 200

The maximum size of a partial spread in H(5, q²) is q³+1

AbstractIn this paper, we show that the largest maximal partial spreads of the hermitian variety H(5,q2) consist of q3+1 generators. Previously, it was only known that q4 is an upper bound for the size of these partial spreads. We also show for q⩾7 that every maximal partial spread of H(5,q2) contains at least 2q+3 planes. Previously, only the lower bound q+1 was known

Effects of a spin-flavour dependent interaction on light-flavoured baryon helicity amplitudes

This paper is a continuation of previous work about the effects of a phenomenological flavour dependent force in a relativistically covariant constituent quark model based on the Salpeter equation on the structure of light-flavoured baryon resonances. Here the longitudinal and transverse helicity amplitudes as studied experimentally in the electro-excitation of nucleon- and $\Delta$ resonances are calculated. In particular the amplitudes for the excitation of three and four star resonances as calculated in a previous model $\mathcal A$ are compared to those of the novel model $\mathcal C$ as well as to existing and partially new experimental data such as e.g. determined by the CB-ELSA collaboration. A brief discussion of some improvements to model $\mathcal C$ is given after the introduction.Comment: 21 pages, 58 figure

Characterization results on weighted minihypers and on linear codes meeting the G(r)iesmer bound

A