THE PROTON SPIN AND GLUEBALL EFFECTS

We consider the smallness of the proton spin measured in polarized lepton–proton scattering experiments. The proton spin is expressed by the matrix element of the flavor singlet axial vector current. Under the PCAC assumption, in which the divergence of the flavor singlet axial vector current is replaced by the pseudoscalar meson η, η′ and glueball ι fields, we get a Goldberger–Treiman type relation. We estimate the coupling constants f0η, f0η′ and f0ι using the U(3)×U(3) current-algebraic approach. Because the estimated f0ι is of the same order as f0η′, the smallness of the proton spin results in gNNι being comparable to gNNπ in magnitude.