We analyze the octet baryon masses and the pionÂkaon-nucleon _-terms in the framework of heavy baryon chiral perturbation theory. We include all terms up-to-and-including quadratic order in the light quark masses, m q . We develop a consistent scheme to estimate low-energy constants related to scalar-isoscalar operators in the framework of resonance exchange involving one-loop graphs. The pertinent low-energy constants can only be estimated up to some finite coefficients. Including contributions from loop graphs with intermediate spin-3Â2 decuplet and spin-1Â2 octet states and from tree graphs including scalar mesons, we use the octet baryon masses and the pion-nucleon _-term to fix all but one of these coefficients. Physical results are insensitive to this remaining parameter. It is also demonstrated that two-loop corrections only modify some of the subleading low-energy constants. We find for the baryon mass in the chiral limit, m # =770\110 MeV. While the corrections of order m 2 q are small for the nucleon, they are still sizeable for the 4, the 7 and the 5. Therefore a definitive statement about the convergence of three-flavor baryon chiral perturbation can not yet be made. The strangeness content of the nucleon is y=0.21\0.20. We also estimate the kaon-nucleon _-terms and some two-loops contributions to the nucleon mass.1997 Academic Press

The strong K − p scattering length is extracted within chiral SU(3) unitary approaches from a very large variety of fits to low-energy K − p scattering data. Very good overall agreement with available scattering data is obtained and the resulting scattering length is compared with the new accurate kaonic hydrogen data from DEAR. The pole structures of the obtained fits to experiment are critically examined.

TheKN system close to threshold is analyzed in view of the new accurate DEAR kaonic hydrogen data. The calculations are performed using chiral SU(3) effective field theory in combination with non-perturbative schemes based on coupled channels. Several variants of such approaches are compared with experimental data and the differences in the results are discussed. Coulomb and isospin breaking effects turn out to be important and are both taken into account. The pole structure of the Λ(1405) resonance close to theKN threshold is critically examined.

Chiral SU(3) effective field theory in combination with a relativistic coupled-channels approach is used to perform a novel analysis of the strong-interaction shift and width in kaonic hydrogen in view of the new accurate DEAR measurements. Questions of consistency with previous K(-)p data are examined. Coulomb and isospin breaking effects turn out to be important and are both taken into account in this work.

We discuss lattice simulations of light nuclei at leading order in chiral effective field theory. Using lattice pion fields and auxiliary fields, we include the physics of instantaneous one-pion exchange and the leading-order S-wave contact interactions. We also consider higher-derivative contact interactions which adjust the S-wave scattering amplitude at higher momenta. By construction our lattice path integral is positive definite in the limit of exact Wigner SU(4) symmetry for any even number of nucleons. This SU(4) positivity and the approximate SU(4) symmetry of the low-energy interactions play an important role in suppressing sign and phase oscillations in Monte Carlo simulations. We assess the computational scaling of the lattice algorithm for light nuclei with up to eight nucleons and analyze in detail calculations of the deuteron, triton, and helium-4.