Comment on 'Supercritical effects and the δ potential'

Recently Loewe and Sanhueza (ibid., vol.23, p.553, (1990)) examined supercritical effects caused by a δ potential acting on a Dirac particle in one dimension and also by a δ-shell potential in three dimensions. Based on the observation that supercritical effects are absent for the δ potential, they suggested that the effects depend on the spatial extension of the potential. The authors point out that the effects are absent for a class of non-local separable potentials in one dimension. The ranges of the potentials can be chosen arbitrarily; the δ potential is a special case.