Exponential suppression of radiatively induced mass in the truncated overlap

A certain truncation of the overlap (domain wall fermions) contains k flavors of Wilson-Dirac fermions. We show that for sufficiently weak lattice gauge fields the effective mass of the lightest Dirac particle is exponentially suppressed in k. This suppression is seen to disappear when lattice topology is non-trivial. We check explicitly that the suppression holds to one loop in perturbation theory. We also provide a new expression for the free fermion propagator with an arbitrary additional mass term. (orig.)