Chiral dynamics in the presence of bound states: kaon–nucleon interactions revisited

We study the S-wave kaon–nucleon interactions for strangeness S=−1 in a novel relativistic chiral unitary approach based on coupled channels. Dispersion relations are used to perform the necessary resummation of the lowest order relativistic chiral Lagrangian. A good description of the data in the K−p, πΣ and πΛ channels is obtained. We show how this method can be systematically extended to higher orders, emphasizing its applicability to any scenario of strong self-interactions where the perturbative series diverges even at low energies. Discussions about the differences to existing approaches employing pseudo-potentials in a regulated Lippmann–Schwinger equation are included. Finally, we describe the resonance content of our meson–baryon amplitudes and discuss its nature.