The nucleon axial isoscalar coupling in quantum chromodynamics sum rules

The correction arising from the three-gluon condensate to the QCD sum rules of the nucleon coupling constant to the axial isoscalar current, gAs, is calculated. It is found that the contribution of the three-gluon condensate can make the sum rules more stable. The resultant theoretical value, gAs = 0.58±0.20, agrees with the phenomenological estimate. The first moments of the spin structure functions for proton, neutron and deuteron are found to be consistent with the improved Ellis-Jaffe sum rules.