Chiral dynamics in the presence of bound states: kaon-nucleon interactionsrevisited

We study the S-wave kaon-nucleon interactions for strangeness S = -1 in a n ovel relativistic chiral unitary approach based on coupled channels. Disper sion 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 metho d can be systematically extended to higher orders, emphasizing its applicab ility to any scenario of strong self-interactions where the perturbative se ries diverges even at low energies. Discussions about the differences to ex isting approaches employing pseudopotentials in a regulated Lippmann-Schwin ger equation are included. Finally, we describe the resonance content of ou r meson-baryon amplitudes and discuss its nature. (C) 2001 Published by Els evier Science B.V.