Impedance, zero energy wavefunction, and bound states

Abstract
We show that the presence, or absence, of bound states in the three‐dimensional Schrödinger equation directly depends on the existence of zeros for a function which is a zero energy solution of the equation and which has the meaning of an impedance in a related equation. Several inequalities that are sufficient to prevent the existence of bound states are obtained from this remark. Some of them are new and bridge the gap between previous results.