Chiral unitary approach to S-wave meson baryon scattering in the strangeness S=0 sector

We study the S-wave interaction of mesons with baryons in the strangeness S=0 sector in a coupled channel unitary approach. The basic dynamics is drawn from the lowest order meson-baryon chiral Lagrangians. Small modifications inspired by models with explicit vector meson exchange in the t channel are also considered. In addition the ππN channel is included and shown to have an important repercussion in the results, particularly in the isospin 3/2 sector. The N^*(1535) resonance is dynamically generated and appears as a pole in the second Riemann sheet with its mass, width, and branching ratios in fair agreement with experiment. A Δ(1620) resonance also appears as a pole at the right position although with a very large width, coming essentially from the coupling to the ππN channel, in qualitative agreement with experiment.