Anomalous Hypercharge Axial Current And The Couplings Of The eta And f_1 (1420) Mesons To The Nucleon

Abstract

It is argued that the precise three flavor symmetry of hadrons is not SU(3)_F but rather U(4)_F restricted to SU(2)_{ud}*SU(2)_{cs}*U(1) and considered in the limit of frozen charm degree of freedom. Within this scheme the only hypercharge generator which is consistent with the Gell-Mann--Nishijima relation appears to be an element of the su(2)_{cs}*u(1) subalgebra as it contains the unit matrix generating the baryon number current. In considering now hypercharge axial transformations, the u(1) generator will give rise to the anomalous U(1)_A axial current and the resulting hypercharge axial current will be anomalous, too. The only anomaly free neutral strong axial current having a well defined chiral limit turns out to be identical (up to a constant factor) with the weak axial current, and the eta meson acquires features of a `masked' strange Goldstone boson. The eta N and f_1(1420)N couplings will now proceed via a purely strange isosinglet axial current and appear strongly suppressed relative to the predictions of the octet quark model. For this reason, loop corrections like the a_0\pi N and KK^*Y triangles to the respective eta NN and f_1(1420)NN vertices acquire importance. Here we calculate them in using effective lagrangians and show that the model developed is convenient for data description beyond the limits of applicability of chiral perturbation theory.