The description of baryons as soliton solutions of effective meson theories for three-flavor (up, down and 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 semileptonic 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 the context of the 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 chirally invariant inclusion of vector meson fields. These extensions are necessary for properly describing 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 made between the collective quantization scheme and the 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 quark flavor dynamics. This is explained for both the collective and the bound state approaches to strangeness.
Understanding the flavor symmetry breaking and nucleon flavor-spin structure within the chiral quark model
