Unbound states by analytic continuation in the coupling constant

The energies and widths of resonance states are determined by the analytic continuation of bound-state energies as functions of a potential strength parameter (open-quotes the coupling constantclose quotes). Various numerical examples show the applicability of the method to systems decaying to two- and three-body channels. The examples include unbound states of the nuclei 5He, 5Li, 9Be, and 9B, described in α+N and α+α+N microscopic cluster models. Some states considered are controversial. Here they are well defined, and their questionable features are understood to arise from their proximity to the complex-energy region of unphysical resonances with negative energies and positive widths. copyright 1999 The American Physical Society