Nonorthogonal Quasistationary States

Abstract

The nonorthogonality of unstable states with common decay channels is considered. The mechanism of the formation of nonorthogonal unstable states through the mixing of orthogonal stable levels is analyzed within the framework of the two-level problem. If the quasi-stationary states are nonorthogonal, the change of the total number of systems (particles) with time cannot be described by a sum of exponen-tials, and the energy spectrum of the decay products cannot be reduced to a sum of Breit-Wigner terms. In the special case of two overlapping nonorthogonallevels the decay law (40) holds, which corresponds to the presence of a second-order pole in the scattering matrix.