Near-threshold excitation of continuum resonances

We examine the excitation of continuum-state resonances close to the threshold, paying particular attention to the breakdown of the Markov approximation and the consequences of this for initial-state time dependences and final-state spectra. Several theoretical dressed-state alternative descriptions are analyzed and compared: the nonperturbative coupling of a discrete state to a structured continuum with a threshold, the complete Fano diagonalization of the interacting system, and finally a partial diagonalization of the bound-state couplings to reveal the origin of dressed-state stabilization and partial decay suppression observed in this model.