The Spin of the Nucleon in Effective Models.pdfVIP

The Spin of the Nucleon in Effective Models∗ H. Weigel† Institute of Theoretical Physics, T¨ubingen University Auf der Morgenstelle 14, D–72076 T¨ubingen, Germany The three flavor soliton approach for baryons is utilized to discuss effects of flavor symmetry breaking in the baryon wave–functions on axial current matrix elements. The flavor content of the singlet axial cur rent matrix elements, that parameterizes the quark spin contribution to the total angular momentum, is disentangled and studied as a function of the effective flavor symmetry breaking. Here the nucleon 1 and the Λ–hyperon are considered. 0 0 2 1 Introduction t c Even though the fundamental theory for the strong interaction processes of hadrons, Quantum O Chromodynamics (QCD), is well established, hadron properties can unfortunately not be computed 7 directly. However, QCD contains a hidden expansion parameter, the number (NC ) of color degrees 1 of freedom, that is beneficial for model building. For arbitrarily large NC , QCD becomes equivalent 1 to a theory of weakly interacting mesons [1]. That is, the meson interaction strengths scale like 1/NC while baryon masses and radii scale like NC and N 0 , respectively [2]. Meson Lagrangians may v C 6 possess localized solutions to the field equations with finite field energy: solitons. Their energies scale 3 2 inversely with the meson coupling and their extensions approach constants as the coupling increases. 0 These analogies lead to the conjecture that baryons emerge as solitons in the effective meson theory 1 that is