On the axial-vector form factor of the nucleon and chiral symmetry

We consider the chiral Lagrangian with nucleon, isobar, and pion degrees of freedom. The baryon masses and the axial-vector form factor of the nucleon are derived at the one-loop level. We explore the impact of using on-shell baryon masses in the loop expressions. As compared to results from conventional chiral perturbation theory we find significant differences. An application to QCD lattice data is presented. We perform a global fit to the available lattice data sets for the baryon masses and the nucleon axial-vector form factor, and determine the low-energy constants relevant at $$\hbox {N}^3$$ N 3 LO for the baryon masses and at $$\hbox {N}^2$$ N 2 LO for the form factor. Partial finite-volume effects are considered. We point out that the use of on-shell masses in the loops results in non-analytic behavior of the baryon masses and the form factor as function of the pion mass, which becomes prominent for larger lattice volumes than presently used.

SU(3) STRUCTURE DEPENDENCE IN π→eνγ AND K→eνγ DECAYS

We compute structure-dependent form factors for both π→eνγ and K→eνγ decays using the SU(3) linear σ-model. Meson loop contributions reduce the axial-vector form factor FA(0) by about 40% in both cases. The predicted ratio γ=FA(0)/FV(0) for π→eνγ and sum |FA(0)+FV(0)| for π→eνγ and K→eνγ decays are all in excellent agreement with data.