SIMULTANEOUS ANALYSIS OF THE 4-PI-NU INVARIANT AMPLITUDES AT LOW ENERGIES IN TERMS OF RATIONAL SERIES AND EVALUATION OF THE SIGMA-COMMUTATOR

A simultaneous analysis of the four invariant πN amplitudes in terms of rational series which automatically fulfil fixed- t analyticity is performed. The experimental input consisted of the experimental phase-shift solutions available at present. The analysis was repeated at 22 t-values between t=−0.5 (GeV)2 and the forward direction. From the resulting poles and zeros we recalculate the unphysical-region amplitudes and the current algebra σ-term. The relations of the trajectories of effective poles and zeros to the N*, Δ* resonances and their consistency with dual models for the πN also are discussed. © 1979, Società Italiana di Fisica. All rights reserved.