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, pi Sigma and pi Lambda 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 pseudopotentials in a regulated Lippmann-Schwinger equation are included. Finally, we describe the resonance content of our meson-baryon amplitudes and discuss its nature. (C) 2001 Published by Elsevier Science B.V.