S11-N(1535) and -N(1650) resonances in meson-baryon unitarized coupled channel chiral perturbation theory -: art. no. 116008

The s-wave meson-baryon scattering is analyzed for the strangeness S = 0 sector in a Bethe-Salpeter coupled channel formalism incorporating chiral symmetry. Four channels have been considered: piN, etaN, K Lambda, K Sigma. The needed two-particle irreducible matrix amplitude is taken from lowest order chiral perturbation theory in a relativistic formalism and low energy constants are fitted to the elastic piN phase shifts and the pi (-) p-->etan and pi (-) p-->K-0 Lambda cross section data. The position of the complex poles in the second Riemann sheet of the scattering amplitude determines masses and widths of the S-11-N(1535) and -N(1650) resonances, in reasonable agreement with experiment. A good overall description of data, from piN threshold up to 2 GeV, is achieved, keeping in mind that the two-pion production channel has not been included.