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In coupled-channel models the poles of the scattering S-matrix are located ondifferent Riemann sheets. Physical observables are affected mainly by polesclosest to the physical region but sometimes shadow poles have considerableeffect, too. The purpose of this paper is to show that in coupled-channelproblem all poles of the S-matrix can be calculated with properly constructedcomplex-energy basis. The Berggren basis is used for expanding thecoupled-channel solutions. The location of the poles of the S-matrix werecalculated and compared with an exactly solvable coupled-channel problem: theone with the Cox potential. We show that with appropriately chosen Berggrenbasis poles of the S-matrix including the shadow ones can be determined.

Shadow poles in a coupled-channel problem calculated with Berggren basis