Causality and analyticity in πN resonant wavesresonant waves

Abstract

The requirements of causality and finite range lead to analytic expressions for theS-matrix in πN resonant waves. The singularities in the complex energy plane are obtained. From them it is easy to calculate the mass and width of the resonances. It is shown that a resonance is a rather complex phenomenon characterized by several mass values which can be very different. For instance, the strange behaviour of theP 11 resonant state is due to this fact.