Effect in level spectrum of three resonantly interacting particles

Properties of a physical system are usually calculated starting from given interparticle forces. But there are certain cases when the levels appear as a direct result of the existence of some other levels. The effect under consideration is an example of such a relation between two- and three-body levels. It is a rather rigid relation: it does not depend on actual form of two-body forces which are only assumed to be of short range; the effect exists whatever the forces are, if only they give rise to certain two-body levels. The effect is described through the example of a simple three-body system - three identical spinless neutral particles. Every pair of these particles is supposed to form a bound or virtual state with zero angular momentum and small energy e0. (Auth.)