Instantons and the spin of the nucleon -: art. no. 094028

Motivated by measurements of the flavor singlet axial coupling constant of the nucleon in polarized deep inelastic scattering we study the contribution of instantons to Okubo-Zweig-Iizuka rule (OZI) violation in the axial-vector channel. We consider, in particular, the f(1)-a(1) meson splitting, the flavor singlet and triplet axial coupling of a constituent quark, and the axial coupling constant of the nucleon. We show that instantons provide a short distance contribution to OZI violating correlation functions which is repulsive in the f(1) meson channel and adds to the flavor singlet three-point function of a constituent quark. We also show that the sign of this contribution is determined by positivity arguments. We compute long distance contributions using numerical simulations of the instanton liquid. We find that the isovector axial coupling constant of a constituent quark is (g(A)(3))(Q)=0.9 and that of a nucleon is g(A)(3)=1.28, in good agreement with experiment. The flavor singlet coupling of a quark is close to one, while that of a nucleon is suppressed, g(A)(0)=0.77. However, this number is larger than the experimental value g(A)(0)=(0.28-0.41).