Higher resonance contamination of πNN couplings obtained via the three-point function method in QCD sum rules

Abstract

We investigate the size of potential higher pseudoscalar resonance contaminations of the estimates of isospin-conserving and isospin-violating πNN couplings obtained using the three-point function method in QCD sum rules. For the isospin-conserving case it is shown that conventional models of the isovector pseudoscalar spectral function imply resonance decay constants large enough to create significant contaminations, and that assuming these models are incorrect, and that the decay constants are actually much smaller, implies physically implausible values for the flavor-breaking quark condensate ratios. For the isospin-violating case it is shown explicitly that such resonance contamination is unavoidably present and precludes using the three-point function method as a means of estimating the at present unmeasured isospin-violating πNN couplings.