Axial exchange currents and nucleon spin
Facultad de Ciencias, Universidad de Salamanca, Plaza de la Merced s/n, E-37008, Salamanca, Spain
2 Institut für Theoretische Physik, Universität Tübingen, Auf der Morgenstelle 14, D-72076, Tübingen, Germany
Accepted: 28 March 2006
Published online: 2 May 2006
We calculate the axial couplings g A 8(0) and g A 0(0) related to the spin of the nucleon in a constituent quark model. In addition to the standard one-body axial currents, the model includes two-body axial exchange currents. The latter are necessary to satisfy the Partial Conservation of Axial Current (PCAC) condition. For both axial couplings we find significant corrections to the standard quark model prediction. Exchange currents reduce the valence quark contribution to the nucleon spin and afford an interpretation of the missing nucleon spin as orbital angular momentum carried by nonvalence quark degrees of freedom.
PACS: 12.39.Jh Nonrelativistic quark model – / 11.40.Ha Partially conserved axial-vector currents – / 14.40.Aq π, K, and η mesons – / 13.60.Hb Total and inclusive cross sections (including deep-inelastic processes) –
© Società Italiana di Fisica and Springer-Verlag, 2006