Nucleon spin structure functions in the chiral quark model

We show that the nucleon spin structure functions, as extracted from the recent experiments carried out by the European Muon Collaboration (EMC), the SLAC E143 and E154 Collaborations, and the Spin Muon Collaboration (SMC), can be understood quantitatively in the chiral quark model, both for the measured first moment Γ1=∫01g1(x)dx and the functional form (or the shape) of the spin structure function g1(x) (as a function of the Bjorken scaling variable x). The success suggests strongly that the nonperturbative effects due to Goldstone bosons play a significant role, and should be taken into account, in the kinematic range of the momentum transfer squared Q2 of several GeV2.