A new fit of a chirally motivated coupled-channels model for meson-baryon interactions is presented including the recent SIDDHARTA data on the 1s level characteristics of kaonic hydrogen. The kaon-nucleon amplitudes generated by the model are fully consistent with our earlier studies. We argue that a sharp increase of the real part of the in-medium K − p amplitude at subthreshold energies provides a link between the shallowK-nuclear optical potentials obtained microscopically from thresholdKN interactions and the phenomenological deep ones deduced from kaonic atoms data. The impact on the A-dependence of the Λ-hypernuclear formation rates measured in reactions with stopped kaons is discussed too.

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We analyze the ηN interaction using a coupled channel separable potential model that implements the chiral symmetry. The model predicts an ηN stattering length a ηN ≈ 0.7 fm and in-medium subthreshold attraction most likely sufficient to generate η-nuclear bound states. The energy dependence of the ηN amplitude and pole content of the model are discussed. An idea of the same origin of the baryon resonances N (1535) and N (1650) is presented.

The effective separable meson-baryon potentials are constructed to match the equivalent chiral amplitudes up to the second order in external meson momenta. We fit the model parameters (low energy constants) to the threshold and low energy K − p data. In the process, the K − -proton bound state problem is solved exactly in the momentum space and the 1s level characteristics of the kaonic hydrogen are computed simultaneously with the available low energy K − p cross sections. The model is also used to describe the πΣ mass spectrum and the energy dependence of the K − n amplitude.

Abstract. We present an exact solution to the K − -proton bound-state problem formulated in the momentum space. The 1s level characteristics of the kaonic hydrogen are computed simultaneously with the available low-energy K − p data. In the strong-interaction sector the meson-baryon interactions are described by means of an effective (chirally motivated) separable potential and its parameters are fitted to the experimental data.