Pion loop fluctuations of constituent quarks and baryons

The implications of the pion (meson) degrees of freedom for baryon properties, taken at the constituent quark and baryon levels are compared. It is shown that there is a dramatic qualitative difference between two approaches.Comment: 3 pages, contribution at the 16th Int. Conf. on Few Body Problems (Taipei, March 6-10, 2000

Baryon Magnetic Moments and Axial Coupling Constants with Relativistic and Exchange Current Effects

The large relativistic corrections to the constituent quark current operators improve the predictions for the axial couplings of the baryons, but worsen those for their magnetic moments. The exchange current corrections that are associated with flavor and spin dependent hyperfine interactions between the quarks with a form suggested by pseudoscalar meson exchange can compensate the relativistic corrections to the baryon magnetic moments. This is demonstrated by a calculation of the magnetic moments of the non-strange and strange baryons using wave functions and exchange current operators, which correspond to a recent phenomenological spin- and flavor dependent interquark interaction model with a linear confining interaction, which yields a spectrum close to the empirical one. The possibility that part of the flavor and spin dependent interaction could be due to vector and axial-vector exchange is explored.Comment: Confinement exchange current contribution included, results improved, coauthor list expande

Photoproduction of Baryons Decaying into N pi and N eta

A combined analysis of photoproduction data on \gamma p to \pi N, eta N was performed including the data on K Lambda and K Sigma. The data are interpreted in an isobar model with s--channel baryon resonances and pi, rho,(omega), K, and K^* exchange in the t--channel. Three baryon resonances have a substantial coupling to eta N, the well known N(1535)S_{11}, N(1720)P_{13}, and N(2070)D_{15}. The inclusion of data with open strangeness reveals the presence of further new resonances, N(1840)P_{11}, N(1875)D_{13} and N(2170)D_{13}.Comment: 13 pages, 14 figure

NN interaction in a Goldstone boson exchange model

Adiabatic nucleon-nucleon potentials are calculated in a six-quark nonrelativistic chiral constituent quark model where the Hamiltonian contains a linear confinement and a pseudoscalar meson (Goldstone boson) exchange interaction between quarks. Calculations are performed both in a cluster model and a molecular orbital basis, through coupled channels. In both cases the potentials present an important hard core at short distances, explained through the dominance of the [51]_{FS} configuration, but do not exhibit an attractive pocket. We add a scalar meson exchange interaction and show how it can account for some middle-range attraction.Comment: 32 pages with 12 eps figures incorporated, RevTeX. Final version published in PR

The π−\pi-Gluon Exchange Interaction Between Constituent Quarks

The interaction mediated by irreducible pion and gluon exchange between constituent quarks is calculated and shown to have a strong tensor component, which tends to cancel the pion exchange tensor interaction between quarks. Its spin-spin component is somewhat weaker than the pion exchange spin-spin interaction, while its central and spin-orbit components are small in comparison to the corresponding single gluon exchange interactions. The combination of the $\pi-$gluon exchange interaction with the single pion exchange interaction and a weak gluon exchange interaction between constituent quarks has the qualitative features required for understanding the hyperfine splittings of the spectra of the nucleon and the $\Delta$ resonances.Comment: LaTeX, 17 pages, 5 Postscript figure

Relativistic quark model and pentaquark spectroscopy

The relativistic five-quark equations are found in the framework of the dispersion relation technique. The solutions of these equations using the method based on the extraction of leading singularities of the amplitudes are obtained. The five-quark amplitudes for the low-lying pentaquarks are calculated under the condition that flavor SU(3) symmetry holds. The poles of five-quark amplitudes determine the masses of the lowest pentaquarks. The mass spectra of pentaquarks which contain only light quarks are calculated. The calculation of pentaquark amplitudes estimates the contributions of three subamplitudes. The main contributions to the pentaquark amplitude are determined by the subamplitudes, which include the meson states.Comment: 22 pages, pd

Strong decays of N∗(1535)N^{*}(1535) in an extended chiral quark model

The strong decays of the $N^{*}(1535)$ resonance are investigated in an extended chiral quark model by including the low-lying $qqqq\bar{q}$ components in addition to the $qqq$ component. The results show that these five-quark components in $N^{*}(1535)$ contribute significantly to the $N^{*}(1535)\to N\pi$ and $N^{*}(1535)\to N\eta$ decays. The contributions to the $N\eta$ decay come from both the lowest energy and the next-to-lowest energy five-quarks components, while the contributions to the $N\pi$ decay come from only the latter one. Taking these contributions into account, the description for the strong decays of $N^{*}(1535)$ is improved, especially, for the puzzling large ratio of the decays to $N\eta$ and $N\pi$.Comment: 6 pages, 1 figur