Vector-meson–baryon coupling constants in QCD sum rules

The external-field quantum chromodynamics (QCD) sum rules method is used to evaluate the coupling constants of the vector mesons ρ and ω to the nucleon and the $\Lambda ,\Sigma$, and Ξ baryons. It is shown that these coupling constants as calculated from QCD sum rules are consistent with SU(3)-flavor relations. By assuming ideal mixing, this leads to a determination of the $F/(F+D)$ ratio of the vector-meson octet: we find ${\alpha }_v=1$ and ${\alpha }_m=0.18$ for the vector and the magnetic $F/(F+D)$ ratios, respectively. The sensitivity of the results to the unknown vacuum susceptibility ζ is discussed. The coupling constants with SU(3)-breaking effects taken into account are also calculated.

Figure 1

The Borel mass dependence of the vector and tensor coupling constants of ρ and ω to the nucleon for average values of the vacuum parameters and the susceptibilities.

Figure 2

Same as Fig. 1 but for the vector and tensor coupling constants of ρ and ω to the hyperons in the SU(3) limit.

Figure 3

The dependence of ${\alpha }_v=F/(F+D)$ on the susceptibility ζ for the sum rules at structures I and II, at $M^2=1$ GeV${}^2$ and for the average values of the other vacuum parameters.

Figure 4

Same as Fig. 3 but for the dependence of $g_N^{\rho }/g_N^{\omega }$.