We report on a calculation of higher electromagnetic multipole moments of baryons in a non-covariant quark model approach. The employed method is based on the underlying spin-flavor symmetry of the strong interaction and its breaking.We present resul
ts on magnetic octupole moments of decuplet baryons and discuss their implications.
We calculate the axial $Nto Delta(1232)$ and $Nto N^{star}(1440)$ transition form factors in a chiral constituent quark model. As required by the partial conservation of axial current ($PCAC$) condition, we include one- and two-body axial exchange cu
rrents. For the axial $Nto Delta(1232)$ form factors we compare with previous quark model calculations that use only one-body axial currents, and with experimental analyses. The paper provides the first calculation of all weak axial $Nto N^{star}(1440)$ form factors. Our main result is that exchange currents are very important for certain axial transition form factors. In addition to improving our understanding of nucleon structure, the present results are relevant for neutrino-nucleus scattering cross section predictions needed in the analysis of neutrino mixing experiments.
The charge radii and quadrupole moments of baryons with nonzero strangeness are calculated using a parametrization method based on the symmetries of the strong interaction.
To obtain further information on the geometric shape of the nucleon, the proton charge form factor is decomposed into two terms, which are connected respectively with a spherically symmetric and an intrinsic quadrupole part of the protons charge dens
ity. Quark model relations are employed to derive expressions for both terms. In particular, the protons intrinsic quadrupole form factor is obtained from a relation between the N -> Delta and neutron charge form factors. The proposed decomposition shows that the neutron charge form factor is an observable manifestation of an intrinsic quadrupole form factor of the nucleon. Furthermore, it affords an interpretation of recent electron-nucleon scattering data in terms of a nonspherical distribution of quark-antiquark pairs in the nucleon.
