Nonthreshold anomalous time advance in multichannel scattering

We investigate scattering in a one-dimensional two-channel system using a model that is analytically tractable. We find anomalously large time advance over a small energy range of the transmission in the incident channel. This time advance for transmission occurs at energies above threshold of the second channel. Since this feature is related to the phase shifts of the interaction it is not peculiar to the form of the interaction. The anomalous times advance can be related to the pole structure of the S matrix, in particular resonant and shadow poles of the S matrix.