On Friedrichs Model with Two Continuum States
  The Friedrichs model with one discrete state coupled to more than one continuum is studied. The exact eigenstates for the full Hamiltonian can be solved explicitly. The discrete state is found to generate more than one virtual state pole or more than one pair of resonance poles in different Riemann sheets in different situations. The form factors could also generate new states on different sheets. All these states can appear in the generalized completeness relation. 
Zhiguang Xiao, Zhi-Yong Zhou
hep-ph nucl-th quant-ph