Resonance regions determined by a projection-operator formulation

Abstract
A particular well-defined enveloping construction based on the Hermitian representation of the complex-coordinate method combined with a projection-operator argument leads to a rigorous criterion for the existence of a resonance eigenvalue within a given region in the complex energy plane. The geometrical realization of this idea involves the analysis of a certain ichthyoid ‘‘fishlike’’ enveloping construction. Results for a simple model potential are displayed.