Kaon-nucleon scattering from chiral Lagrangians

The s-wave K ± N scattering amplitude is computed up to one-loop order corresponding to next-to-next-to-leading order (or N 2LO in short) in chiral perturbation with a heavy-baryon effective chiral Lagrangian. Constraining the low-energy constants by on-shell scattering lengths, we predict the off-shell s-wave K − N scattering amplitudes relevant to kaonic atoms and K − condensation in “nuclear star” matter. The crossing-even one-loop corrections are found to play an important role in determining the higher-order chiral corrections.