Full Fermion-Boson Vertex Function Derived in terms of the   Ward-Takahashi Relations in Abelian Gauge Theory
  I present an approach to derive the full fermion-boson vertex function in four-dimensional Abelian gauge theory in terms of a set of normal (longitudinal) and transverse Ward-Takahashi relations for the fermion-boson and axial-vector vertices in momentum space in the case of massless fermion. Such a derived fermion-boson vertex function should be satisfied both perturbatively and non-perturbatively. I show that, by an explicit computation, such a derived full fermion-boson vertex function to one-loop order leads to the same result as one obtained in perturbation theory. 
Han-xin He