Effects of the $\Sigma$N channels on the spin-orbit force in $\Lambda$-hypernuclei are investigated. It is found that the cancellation between the symmetric and the antisymmetric $\Lambda$N spin-orbit force becomes more complete when the contribution from the $\Sigma$N channels is included. This may be the one of the reasons why the observed LS splitting of the $\Lambda$ single particle energy is very small.
Categories: hep-ph