Hyperon nucleon scattering at next-to-leading order in chiral perturbation theory

The hyperon-nucleon interaction has not been studied as intensively as the nucleon-nucleon interaction. In my Diploma thesis I have investigated the usefulness of the ChPT approach using SU(3)-flavour symmetry for low-energy hyperon-nucleon scattering, extending the chiral expansion up to second order. We constructed a SU(3) invariant potential, consisting of a long- and a short-range part. The long range physics is governed by one-Goldstone boson exchange while the short-range part is determined by contact interaction using 23 free parameters. Out of those only the S-wave related could be determined by a fix to low-energy hyperon-nucleon cross-sections, the remaining 10 P-wave related low-energy constants are still undetermined due to the scarcity and poor quality of the scattering data. We could obtain a good description of the data, even at lab momenta that exceed those that have been used for the fitting procedure. The value of chi squared could be reduced compared to the leading order work. For a cut-off in the range of 550 MeV-700 Mev we obtained a correctly bound hypertriton. However the predictions of the angular dependence remains optimizable. This problem might be overcome once we find a efficient way to fix the P-wave related low-energy constants.