The Pion-Nucleon Form Factor From QCD Sum Rules

Abstract

QCD sum rules are used to calculate the $q^2$ dependence of the $\pi NN$ coupling $g_{\pi NN} (q^2)$ in the spacelike region $0.5 \ {\mbox{GeV}}^2 \lesssim q^2 \lesssim 1.5\ {\mbox{GeV}}^2$. We study the Borel sum rule for the three point function of one pseudoscalar and two nucleon currents up to order four in the operator product expansion. The Borel transform is performed with respect to the nucleon momenta, whereas the momentum $q^2$ of the pseudoscalar vertex is kept fixed at spacelike values. The results can be well fitted using a monopole form with a cutoff mass of about $\Lambda_\pi \approx 800 \ {\mbox{MeV}}.