The Nucleon Axial Isoscalar Coupling and First Moments of p,n, d Spin Structure Functions

The nucleon coupling constant to the axial isoscalar current, g_A^s, is calculated in the framework of QCD sum rules by including the effects of the three-gluon condensates. The contribution from the polarized strange sea quarks to g_A^s is extracted in a constituent quark model with a QCD modification. The combined resultant theoretical value, g_A^s = 0.60±0.20, agrees with the experimental estimate. The first moments of the proton, neutron and deuteron spin structure functions are evaluated and compared with the experimental data.