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Remarks on the complex branch points in pi-N scattering amplitude and the multiple poles structure of resonances (1112.5025v1)
Published 21 Dec 2011 in nucl-th and hep-ph
Abstract: A simple heuristic argument to understand the existence of branch points in the unphysical sheet for pi-N scattering amplitude is presented. It is based on a hypothesis that the singularity structure of the pi-N scattering amplitude is a smooth varying function of the pion mass. We find that, in general, multiple poles structure of a resonance is a direct mathematical consequence when additional Riemann surface is included in the study and the two-pole structure found to correspond to the Roper resonance is a good example.
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