The [formula omitted] ratio and meson–baryon couplings from QCD sum rules II

Abstract

Using QCD sum rules, we compute the diagonal meson–baryon couplings, πNN , ηNN , πΞΞ , ηΞΞ , πΣΣ and ηΣΣ , from the baryon–baryon correlation function with a meson: i ∫ d 4x e iq·x 〈0|TJ B(x) J ̄ B(0)|M(p)〉 . The calculations are performed to leading order in p μ by considering the two separate Dirac structures, iγ 5γ μp μ and γ 5σ μνq μp ν separately. We first improve the previous sum rule calculations on these Dirac structures for the πNN coupling by including three-particle pion wave functions of twist 4 and then extend the formalism to calculate the other couplings, ηNN , πΞΞ , ηΞΞ , πΣΣ and ηΣΣ . 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.