77 v 1 2 5 O ct 2 00 2 Chiral dynamics in systems with strangeness

In this talk a brief review of several problems involving systems with strangeness is made. In the first place one shows how the Λ(1405), Λ(1670) and Σ(1620) states, for S = −1, and the Ξ(1620) for S = −2 are generated dynamically in the context of unitarized chiral perturbation theory. The results for the K̄N interaction are then used to evaluate the K−d scattering length. Results obtained for the kaon selfenergy in a nuclear medium within this approach, with application to K− atoms, are also mentioned. Finally a few words are said about recent developments in the weak decay of Λ hypernuclei and the puzzle of the Γn/Γp ratio. 1 Spectra of low lying strange baryons The combination of unitary techniques together with chiral dynamics of meson and baryon systems already used in [1] and [2] to study low-energy KN scattering, has reached a certain maturity, it has been made more systematic and it has also been applied to the study of a large variety of physical processes [3]. The idea behind this work is the use of the unitarity constraints in coupled channels, which provide the imaginary part of the inverse of the scattering T matrix. From there, by means of dispersion relations, or equivalent techniques, one can construct the whole T matrix. In the strangeness S = −1 sector the N/D, or dispersion relation method has been applied in [4] with the result that the T matrix in coupled channels can be written as