Gauge independent Chiral Symmetry Breaking in Quenched QED
  In quenched QED we construct a non-perturbative fermion-boson vertex that ensures the fermion propagator satisfies the Ward-Takahashi identity, is multiplicatively renormalizable, agrees with perturbation theory for weak couplings and has a critical coupling for dynamical mass generation that is strictly gauge independent. This is in marked contrast to the rainbow approximation in which the critical coupling changes by 50% just between the Landau and Feynman gauges. The use of such a vertex should lead to a more believable study of mass generation. 
A.Bashir and M.R.Pennington