Key points are not available for this paper at this time.
The Schwinger-Dyson equation for the fermion propagator in quenched four-dimensional QED is solved using a nonperturbative ansatz for the fermion-photon vertex that satisfies the Ward-Takahashi identity, ensures the multiplicative renormalizability of the fermion equation, and reproduces low-order perturbation theory in the appropriate limit. The fermion propagator then possesses a chiral-symmetry-breaking phase only when the coupling is larger than a critical value ₂0. 92. This critical coupling is almost exactly gauge independent as is the dynamically generated mass, in complete contrast to the popular rainbow approximation.
Curtis et al. (Mon,) studied this question.