Gauge Properties of Hadronic Structure of Nucleon in Neutron Radiative Beta Decay to Order O(alpha/pi) in Standard V - A Effective Theory with QED and Linear Sigma Model of Strong Low--Energy Interactions

Abstract

Within the standard V - A theory of weak interactions, Quantum Electrodynamics (QED) and the linear sigma-model (LsM) of strong low-energy hadronic interactions we analyse gauge properties of hadronic structure of the neutron and proton in the neutron radiative beta-decay. We show that the Feynman diagrams, describing contributions of hadronic structure to the amplitude of the neutron radiative beta-decay in the tree-approximation for strong low-energy interactions in the LsM, are gauge invariant. In turn, the complete set of Feynman diagrams, describing the contributions of hadron-photon interactions in the one-hadron-loop approximation, is not gauge invariant. In the infinite limit of the scalar sigma-meson, reproducing the current algebra results (Weinberg, Phys. Rev. Lett. 18, 188 (1967)), and to leading order in the large nucleon mass expansion the Feynman diagrams, violating gauge invariance, do not contribute to the amplitude of the neutron radiative beta-decay in agreement with Sirlin's analysis of strong low-energy interactions in neutron beta decays. We assert that the problem of appearance of gauge non-invariant Feynman diagrams of hadronic structure of the neutron and proton is related to the following. The vertex of the effective V-A weak interactions does not belong to the combined quantum field theory including the LsM and QED. We argue that gauge invariant set of Feynman diagrams of hadrons, coupled to real and virtual photons in neutron beta decays, can be obtained within the combined quantum field theory including the Standard Electroweak Model (SEM) and the LsM, where the effective V-A vertex of weak interactions is a result of the W^- - electroweak boson exchange.