$πNN$ and Pseudoscalar Form Factors from Lattice QCD

Abstract

The $πNN$ form factor $g_{πNN}(q^2)$ is obtained from a quenched lattice QCD calculation of the pseudoscalar form factor $g_P(q^2)$ of the proton with pion pole dominance. We find that $g_{πNN}(q^2)$ fitted with the monopole form agrees well with the Goldberger-Treiman relation and is much preferred over the dipole form. The monopole mass is determined to be $0.75 \pm 0.14 {\rm GeV}$ which shows that $g_{πNN}(q^2)$ is rather soft. The extrapolated $πN$ coupling constant $g_{πNN} = 12.7 \pm 2.4$ is quite consistent with the phenomenological values. We also compare $g_{πNN}(q^2)$ with the axial form factor $g_A(q^2)$ to check the pion dominance in the induced pseudoscalar form factor $h_A(q^2)$ vis à vis chiral Ward identity.