Four-loop singularities of the massless fermion propagator in quenched three-dimensional QED.

We calculate the three- and four-loop corrections to the massless fermion propagator in three-dimensional quenched quantum electrodynamics with four-component fermions. The three-loop correction is finite and gauge invariant but the four-loop one has singularities except in the Feynman gauge where it is also finite. Our results explicitly show that, up to four loops, gauge-dependent terms are completely determined by lower order ones in agreement with the Landau-Khalatnikov-Fradkin transformation. [ABSTRACT FROM AUTHOR]