Mass-splittings in the baryon octet and the nucleon σ-term in lattice QCD

We calculate in the valence approximation the F and D parameters governing the mass-splittings in the baryon octet. The use of an improved fermion action enables us to go down in quark mass to the SU(3) symmetric point. The F parameter is consistent with its experimental value. On the other hand, the D parameter turns out to be large and shows a strong dependence on the quark mass. This is evidence that the Σ-Λ mass-splitting is not a first-order SU(3) flavour symmetry breaking effect. We also estimate the contribution of the valence quarks to the nucleon σ-term. (orig.)