THE ROLE OF LAMBDA(1405) IN KAON-PROTON INTERACTIONS

S-wave K- p reactions in various channels near threshold are analyzed in heavy-baryon chiral perturbation theory with the Lambda(1405) intro duced as an independent local matter field, This is the approach that predicted the critical density 2 less than or similar to rho(c)/rho(0) less than or similar to 3 for negatively charged kaon condensation. W e show that a low-order chiral perturbation expansion treating the Lam bda(1405) as elementary can describe all threshold data including a do uble-charge-exchange process suppressed at leading order of the chiral expansion in the absence of the Lambda(1405). We also discuss the mec hanism for large imaginary K- N scattering amplitudes and the role of a substantial KN sigma term in S-wave K+ p scattering phase shifts at low energy.