Dynamical chiral symmetry breaking and the fermion--gauge-boson vertex
  We present a workable model for the fermion-photon vertex, which is expressed solely in terms of functions that appear in the fermion propagator and independent of the angle between the relative momenta, and does not explicitly depend on the covariant-gauge parameter. It nevertheless produces a critical coupling for dynamical chiral symmetry breaking that is practically independent of the covariant-gauge parameter and an anomalous magnetic moment distribution for the dressed fermion that agrees in important respects with realistic numerical solutions of the inhomogeneous vector Bethe-Salpeter equation. 
A. Bashir, R. Bermudez, L. Chang and C. D. Roberts
nucl-th hep-lat hep-ph nucl-ex