Conditions on the pion electroproduction and photoproduction form factors in the soft-pion limit

Abstract

Using the Bernard-Kaiser-Lee-Meissner (BKLM) parametrization of the hadronic vertex γ∗N → πN, with γ being a virtual photon, we analyze the restrictions imposed on the form factors (FF) in the limit at which the pion three-momentum and mass go to zero, which is known as the soft-pion limit. We obtain information about the normalization of the FF in this limit using current algebra methods and the hypothesis of partially conserved axial-vector current (PCAC) which is a way to implement chiral symmetry. We relate these FF with those of the W±N → N weak interaction. The present work provides a useful tool to decide whether a certain model isbetter than another, checking whether the corresponding FF satisfy the conditions imposed in the soft-pion limit,which are model independent.