Low energy KN interactions are studied within unitary chiral perturbation theory at next-to-leading order with ten coupled channels. We pay special attention to the recent precise determination of the strong shift and width of the kaonic hydrogen 1s state by the DEAR Collaboration that has challenged our theoretical understanding of this sector of strong interactions. We typically find two classes of solutions, both of them reproducing previous data, that either can or cannot accommodate the DEAR measurements. The former class has not been previously discussed.

Oller et al. Reply: In their Comment, Borasoy et al. [1], criticize our results [2] that accommodate both scattering data and the new accurate measurement by DEAR of the shift and width of kaonic hydrogen. In our calculations we have employed unitary chiral perturbation theory (UCHPT). We discuss why their arguments are irrelevant or do not hold.(1) Borasoy et al. correctly state in their Comment that the interacting kernel employed in the Letter [2] can induce residual cuts in some energy regions above the threshold of the lighter channels ( and ) because of u-crossed exchange of baryons in amplitudes with heavier states. However, these cuts only induce appreciable unitarity deviations in 0 ! 0 at energies lower than 1.4 GeV, where no data exist with which to compare. These deviations are negligible for the and do not appear at all in the rest of channels. UCHPT resums the right-hand cut (or unitarity cut) while the contributions from the other cuts in the interacting kernel are calculated only at a given order in CHPT, by matching with the chiral series order by order. The right-hand cut resummation is justified since the chain of unitarity bubbles is enhanced by the large masses of kaons and baryons [3]. In this way, one reproduces the CHPT results up to a given order, e.g., to Op 2 in [2]. In this scheme, calculating the interacting kernel at higher orders in CHPT will eventually soften the effect of these spurious cuts. If one eliminates the u-channel cuts in the S-wave projections by ad hoc taking them to be constants above some energy value, as in [4], then chiral symmetry as well as crossing are violated even at leading order in CHPT.

Abstract. Motivated by recent experimental results and ongoing measurements, we review the chiral perturbation theory prediction for KL → π ∓ e ± νeγ decays. Special emphasis is given to the stability of the inner bremsstrahlung-dominated relative branching ratio versus the Ke3 form factors, and on the separation of the structure-dependent amplitude in differential distributions over the phase space. For the structure-dependent terms, an assessment of the order p 6 corrections is given, in particular, a full nextto-leading order calculation of the axial component is performed. The experimental analysis of the photon energy spectrum is discussed, and other potentially useful distributions are introduced.

Strange meson-baryon interaction in hot and dense medium: recent progress for a road to GSI/FAIR D Cabrera, L Tolos, J Aichelin et al. Abstract: We construct the complete and minimal O(q 2 ) and O(q 3 ) three-flavour Lorentz invariant chiral meson-baryon Lagrangians for the first time in the literature. We compare with previous three-flavour studies reducing the number of independent monomials and adding new ones that were missing.

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