Jordan blocks and Gamow-Jordan eigenfunctions associated with a degeneracy of unbound states
Jordan blocks and Gamow-Jordan eigenfunctions associated with a degeneracy of unbound states
An accidental degeneracy of unbound states gives rise to a double pole in the scattering matrix, a double zero in the Jost function, and a Jordan chain of length 2 of generalized Gamow-Jordan eigenfunctions of the radial Schr\"odinger equation. The generalized Gamow-Jordan eigenfunctions are basis elements of an expansion in …