On the Strangeness −1 S-wave Meson-Baryon Scattering

We consider meson-baryon interactions in S-wave with strangeness −1. This is a nonperturbative sector populated by plenty of resonances interacting in several two-body coupled channels. We study this sector combining a large set of experimental data. The recent experiments are remarkably accurate demanding a sound theoretical description to account for all the data. We employ unitary chiral perturbation theory up to and including O(p2) to accomplish this aim. The spectroscopy of our solutions is studied within this approach, discussing the rise from the pole content of the two Λ(1405) resonances and of the Λ(1670), Λ(1800), Σ(1480), Σ(1620) and Σ(1750). We finally argue about our preferred solution.