Studying the bound state of the K- p system in the Bethe-Salpeter formalism

We study the s-wave kaon-nucleon bound state with the strangeness S = -1 in the Bethe-Salpeter formalism in the ladder and instantaneous approximations. We solve the Bethe-Salpeter equation of the bound state and obtain the Bethe-Salpeter amplitude. It is shown that the K- p bound state exists in this formalism. We also study the decay width of the bound state based on the Bethe-Salpeter techniques. The mass of this bound state is 1422 MeV, and its decay width is obviously smaller than that of Lambda (1405). These results indicate that there may be some other structures in the observed resonance.