Baryons as Three Flavor Solitons

The description of baryons as soliton solutions of effective meson theories for three flavor (up, down, strange) degrees of freedom is reviewed and the phenomenological implications are illuminated. In the collective approach the soliton configuration is equipped with baryon quantum numbers by canonical quantization of the coordinates describing the flavor orientation. The baryon spectrum resulting from exact diagonalization of the collective Hamiltonian is discussed. The prediction of static properties such as the baryon magnetic moments and the Cabibbo matrix elements for semi--leptonic hyperon decays are explored with regard to the influence of flavor symmetry breaking. In particular, the role of strange degrees of freedom in the nucleon is investigated for both the vector and axial--vector current matrix elements. The latter are discussed extensively within in the context of the {\it proton spin puzzle}. The influence of flavor symmetry breaking on the shape of the soliton is examined and observed to cause significant deviations from flavor covariant predictions on the baryon magnetic moments. Short range effects are incorporated by a chiral invariant inclusion of vector meson fields. These extensions are necessary to properly describe the singlet axial--vector current and the neutron proton mass difference. The effects of the vector meson excitations on baryon properties are also considered. The bound state description of hyperons and its generalization to baryons containing a heavy quark are illustrated. In the case of the Skyrme model a comparison is performed between the collective quantization scheme and bound state approach. Finally, the Nambu--Jona--Lasinio model is employed to demonstrate that hyperons can be described as solitons in a microscopic theory of the quarkComment: 110 pages, minor corrections, submitted as uuencoded file, to appear in Int. J. Mod. Phys.

The parity-violating pion-nucleon coupling constant from a realistic three flavor Skyrme model

We study the parity-violating pion-nucleon coupling $G_\pi$ in the framework of a realistic three flavor Skryme model. We find a sizeable enhancement of $G_\pi \simeq 0.8 ... 1.3 \cdot 10^{-7}$ compared to previous calculations in two-flavor models with vector mesons. This strangeness enhancement stems from induced kaon fields of the chiral soliton and the non-monotoneous dependence on symmetry breaking of the nucleon matrix element of the flavor singlet piece of the operator associated with these induced fields. Both features are sensitive to four quark operators including an $\bar s s$ pair.Comment: 10 pp, LaTeX, uses epsf, 2 figs, small corrections plus additional explanations, value of Gpi somewhat smalle

Hyperons as collective excitations of chiral solitons

According to the large $N_C$ limit of QCD baryons are considered as soliton solutions in effective mesons theories. While the classical solitons dwell in the isospin subgroup of flavor SU(3) hyperon states are generated by canonical quantization of the collective coordinates which describe the flavor orientation of the soliton. The resulting Hamiltonian is diagonalized exactly allowing one to discuss the dependence of various baryon properties on flavor symmetry breaking. In particular axial charges, baryon magnetic moments and radiative decay widths are considered.Comment: 3 pages, uses col2.sty (included), Talk presented at the III Int. Conf. on Hyperons, Charm and Beauty Hadrons, Genova, June--July 199

Radiative Decays of Hyperons in the Skyrme Model: E2/M1 Transitions

We study the radiative decays of $J^\pi=\frac{3}{2}^+$ baryons in the framework of the SU(3) collective approach to the Skyrme model. We present the predictions for the decay widths and the corresponding $E2/M1$ ratios. We find that all considered ratios are negative and of the order of a few percent only. We discuss the effects of flavor symmetry breaking and compare our results to those obtained in related models.Comment: 10 pages LaTeX, no figure

SU(3) Symmetry Breaking and Octet Baryon Polarizabilities

Static polarizabilities of the low--lying $1/2^+$ baryons are studied within the collective coordinate approach to the three flavor generalization of the Skyrme model; in particular, magnetic polarizabilities are considered. Predicted polarizabilities, which result from different treatments of the strange degrees of freedom in this model, are critically compared. Their deviations from the flavor symmetric formulations are discussed.Comment: 11 pages, LaTeX, 4 tables, no figures, final version to be published in Phys. Lett.