NUCLEON SPIN STRUCTURE FUNCTIONS IN THE EFFECTIVE CHIRAL QUARK THEORY

We show that the nucleon spin structure functions, as extracted from t he recent experiments carried out by the European Muon Collaboration ( EMC), the SLAG E143 Collaboration, and the Spin Muon Collaboration (SM C), can be understood quantitatively in the context of the effective c hiral quark theory, both for the measured first moment Gamma(1) = inte gral(0)(1) g(1)(x)dx and the functional form (or the shape) of the spi n structure function g(1)(x) (as a function of the Bjorken scaling var iable x). The surprising success suggests strongly that the nonperturb ative effects due to Goldstone bosons play a significant role, and sho uld be taken into account, in the kinematic range of the momentum tran sferred squared Q(2) Of a, few GeV2. The relation to the meson-baryon picture, now recognized as ''generalized Sullivan processes'', is brie fly discussed.