Comment on “Zero-range potentials for Dirac particles: Scattering and related continuum problems”

In a recent paper, Szmytkowski proposed zero-range potentials for Dirac particles in three space dimensions. On the other hand, there is a theorem, proved by Svendsen a long time ago, which implies that zero-range potentials cannot be defined for the Dirac equation in two and three space dimensions. We discuss a difficulty that underlies Szmytkowski’s approach.