The meson-baryon interaction in s wave in the strangeness S = −1 sector has been studied, employing a chiral SU(3) Lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. The parameters of the Lagrangian have been fitted to a large set of experimental data in different two-body channels, paying special attention to theKN → K reaction, which is particularly sensitive to the NLO terms. With the aim of improving the model in the K production channels, effects of the high spin hyperon resonances (2030) and (2250) have been taken into account phenomenologically.

In this paper, we present a review of recent works on weak decay of heavy mesons and baryons with two mesons, or a meson and a baryon, interacting strongly in the final state. The aim is to learn about the interaction of hadrons and how some particular resonances are produced in the reactions. It is shown that these reactions have peculiar features and act as filters for some quantum numbers which allow to identify easily some resonances and learn about their nature. The combination of basic elements of the weak interaction with the framework of the chiral unitary approach allow for an interpretation of results of many reactions and add a novel information to different aspects of the hadron interaction and the properties of dynamically generated resonances.

A study of the meson-baryon interaction in the S = −1 sector is performed, employing a chiral SU(3) Lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. The model is constrained by a large set of experimental data, paying special attention to processes that are sensitive to the NLO contributions, such as the K − p → K + − , K 0 0 reactions. The consideration of additional cross sections in single isospin channels, K − p → η , η , has been found to provide NLO low-energy constants of rather similar size. The stability of these constants has also been tested by the inclusion of explicit resonant terms. Predictions for new isospin filtering processes, like the I = 1 K 0 L p → K + 0 reaction that could be measured at the proposed secondary K 0 L beam at Jlab, or the weak decay of the b into a J/ and different meson-baryon pairs in I = 0, available at LHCb, are presented. The measurement of such reactions would put valuable constraints on the chiral models describing the S = −1 meson-baryon interaction.

We present a study of the S = −1 meson-baryon interaction, employing a chiral SU(3) Lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. The parameters of the model have been fitted to a large set of experimental scattering data in different two-body channels, to threshold branching ratios, and to the precise SIDDHARTA value of the energy shift and width of kaonic hidrogen. In contrast to other groups, we have taken into consideration thewe found in a previous work to be especially sensitive to the NLO parameters of the chiral Lagrangian. In the present work we also include the Born terms, which usually have very little effect, and find them to be non-negligible in the K − p → KΞ channels, correspondingly causing significant modifications to the NLO parameters. We furthermore show that the importance of the Born terms becomes more visible in the isospin projected amplitudes of the K − p → KΞ reactions. The measurement of processes that filter single isospin components, like the K 0 L p → K + Ξ 0 reaction that could be measured at the proposed secondary K 0 L beam at Jlab, would put valuable constraints on the chiral models describing the meson-baryon interaction in the S = −1 sector.

We explore the possibility that some of the five narrow Ωc resonances recently observed at LHCb could correspond to pentaquark states, structured as meson-baryon bound states or molecules. The interaction of the low-lying pseudoscalar mesons with the ground-state baryons in the charm +1, strangeness −2 and isospin 0 sector is built from t-channel vector meson exchange, using effective Lagrangians. The resulting s-wave coupled-channel unitarized amplitudes show the presence of two structures with similar masses and widths to those of the observed Ωc(3050) 0 and Ωc(3090) 0 . The identification of these resonances with the meson-baryon bound states found in this work would also imply assigning the values 1/2 − for their spin-parity. An experimental determination of the spin-parity of the Ωc(3090) 0 would help in disentangling its structure, as the quark-based models predict its spin-parity to be either 3/2 − or 5/2 − .