Dynamical Meson-baryon Resonances with Chiral Lagrangians

The s-wave meson-baryon interaction is studied using the lowest-order chiral Lagrangian in a unitary coupled-channels Bethe-Salpeter equation. In the strangeness S = −1 sector the low-energy K−p dynamics leads to the dynamical generation of the Λ(1405) as a K̄N state, along with a good description of the K−p scattering observables. At higher energies, the Λ(1670) is also found to be generated dynamically as a KΞ quasibound state for the first time. For strangeness S = 0, it is the S11(1535) resonance that emerges from the coupled-channels equations, leading to a satisfactory description of meson-baryon scattering observables in the energy region around the S11(1535). We speculate on the possible dynamical generation of Ξ resonances within the chiral S = −2 sector as K̄Λ or K̄Σ quasibound states.