Single-particle spin-orbit strengths of the nucleon and hyperons by SU6 quark-model

The quark-model hyperon-nucleon interaction suggests an important antisymme tric spin-orbit component. It is generated from a color analogue of the Fer mi-Breit interaction dominating in the one-gluon exchange process between q uarks. We discuss the strength S-B of the single-particle spinorbit potenti al, following the Scheerbaum's prescription. Using the SU6 quark-model bary on-baryon interaction which was recently developed by the Kyoto-Niigata gro up, we calculate NN, Lambda N and Sigma N G-matrices in symmetric nuclear m atter and apply them to estimate the strength S-B. The ratio of S-B to the nucleon strength S-N similar to -40 MeVfm(5) is S-Lambda/S-N similar to 1/5 and S-Sigma/S-N similar to 1/2 in the Born approximation. The G-matrix cal culation of the model FSS modifies S-Lambda to S-Lambda/S-N similar to 1/12 . For S-N and S-Sigma, the effect of the short-range correlation is compara tively weak against meson-exchange potentials with a short-range repulsive core. The significant reduction of the Lambda single-particle potential ari ses from the combined effect of the antisymmetric LS force, the flavor-symm etry breaking originating from the strange to up-down quark-mass difference , as well as the effect of the short-range correlation. The density depende nce of S-B is also examined. (C) 2000 Elsevier Science B.V. All rights rese rved.