Nucleon spin structure functions in the chiral quark model

We show that the nucleon spin structure functions, as extracted from the re cent experiments carried out by the European Muon Collaboration (EMC), the SLAG E143 and E154 Collaborations, and the Spin Muon Collaboration (SMC), c an be understood quantitatively in the chiral quark model, both for the mea sured first moment Gamma(1) = f(0)(1)g(1)(x)dx and the functional form (or the shape) of the spin structure function g(1)(x) (as a function of the Bjo rken scaling variable x). The success suggests strongly that the nonperturb ative effects due to Goldstone bosons play a significant role, and should b e taken into account, in the kinematic range of the momentum transfer squar ed Q(2) of several GeV2. (C) 1999 Published by Elsevier Science B.V. All ri ghts reserved.