A PHENOMENOLOGICAL MODEL FOR THE SPIN-DEPENDENT STRUCTURE FUNCTIONS

A model for the polarized proton, neutron and deuteron structure funct ions embodying various features expected from the theory is presented. Each structure function is constructed from its asymptotic x behaviou rs, consistent with theoretical expectations at large x and small x, w hile the Q(2)-dependence is obtained using the perturbative QCD evolut ion equations. By using QCD improvements on the first moments of vario us distributions, and including, from axial anomaly, a direct gluonic contribution to g(1), good agreement with data on polarized deep inela stic scattering is obtained. Assuming that this gluonic component can be absorbed in a redefined polarized quark density, we reproduce the u nexpected results on the Ellis-Jaffe sum rule and on spin content of t he nucleon with no need of an initially strange sea quark polarization .