We study the S-wave interaction of mesons with baryons in the strangeness $S=0\mathrm{}$ 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 $\pi \pi N$ channel is included and shown to have an important repercussion in the results, particularly in the isospin 3/2 sector. The $N^{*}\mathrm{}\left(1535\right)\mathrm{}$ 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 $\Delta \mathrm{}\left(1620\right)\mathrm{}$ resonance also appears as a pole at the right position although with a very large width, coming essentially from the coupling to the $\pi \pi N$ channel, in qualitative agreement with experiment.

• Received 31 October 2001

DOI:https://doi.org/10.1103/PhysRevC.65.035204