The F/D ratio and meson-baryon couplings from QCD sum rules II

Using QCD sum rules, we compute the diagonal meson-baryon couplings, pi NN, eta NN, pi Xi Xi, eta Xi Xi, pi Sigma Sigma and eta Sigma Sigma, from the baryon-baryon correlation function with a meson: i integral d(4) x e(iq.x)(O/T J(B)(x)(J) over bar(B)(0) / M (p)). The calculations are performed to leading order in p(mu) by considering the two separate Dirac structures, i gamma (5) gamma mu p(mu) and gamma (5) sigma mu nu q(mu)p(nu) separately. We first improve the previous sum rule calculations on these Dirac structures for the pi NN coupling by including three-particle pion wave functions of twist 4 and then extend the formalism to calculate the other couplings, eta NN, pi Xi Xi, eta Xi Xi, pi Sigma Sigma and eta Sigma Sigma. In the SU(3) symmetric limit, we identify the terms responsible For the F/D ratio in the OPE by matching the obtained couplings with their SU(3) relations. Depending on the Dirac structure considered, we find different identifications for the F/D ratio. The couplings including the SU(3) breaking effects are also discussed within our approach. (C) 2000 Elsevier Science B.V. All rights reserved.