Deconstructing the vertex Ansatz in three-dimensional quantum electrodynamics

We consider the problem of designing an Ansatz for the fermion-photon vertex function, using three-dimensional quantum electrodynamics as a test case. In many existing studies, restrictions have been placed on the form of the vertex Ansatz by making the unsubstantiated assumption that in the quenched, massless limit the Landau gauge Dyson-Schwinger equations admit a trivial solution. We demonstrate, without recourse to this assumption, the existence of a nonlocal gauge in which the fermion propagator is the bare propagator. This result is used to provide a viable Ansatz for part of the vertex function.