Herbert Weigel — Page 2

arXiv1997

Generalization of the Bound State Model

In the bound state approach the heavy baryons are constructed by binding, with any orbital angular momentum, the heavy meson multiplet to the nucleon considered as a soliton in an effective meson theory. We point out that this picture misses an entire family of states, labeled by a different angular momentum quantum number, which are expected to exist according to the geometry of the three-body constituent quark model (for N_C=3). To solve this problem we propose that the bound state model be generalized to include orbitally excited heavy mesons bound to the nucleon. In this approach the missing angular momentum is ``locked-up'' in the excited heavy mesons. In the simplest dynamical realization of the picture we give conditions on a set of coupling constants for the binding of the missing heavy baryons of arbitrary spin. The simplifications made include working in the large M limit, neglecting nucleon recoil corrections, neglecting mass differences among different heavy spin multiplets and also neglecting the effects of light vector mesons.

hep-ph↗

arXiv1996

Hidden Structure in a Lagrangian for Hyperfine Splitting of the Heavy Baryons

We investigate the hyperfine splitting of the heavy baryons in the bound-state approach. We start with an ordinary relativistic Lagrangian which has been extensively used to discuss finite mass corrections to the heavy limit predictions. It turns out that the dominant contribution arises from terms which do not manifestly break the heavy spin symmetry. The actual heavy spin violating terms are uncovered by carefully performing a 1/M expansion of this Lagrangian.

hep-ph↗

arXiv1996

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 quark

hep-ph↗