Phenomenological SU(6) breaking of baryon wave functions and the chromodynamic spin-spin force

A contradiction is found between two successful models of SU(6) breaking. A quark-model mixing scheme (56,0⁺) + (70,0⁺) for the baryon octet has been devised to explain the ratio F₂ᵉⁿ(x)F₂ᵉᵖ(x) in the valence-quark region and explains naturally other departures from the usual SU(6) predictions. On the other hand, the gluon-exchange model of SU(6) breaking accounts satisfactorily for the hadron spectrum splittings. The spin-spin contribution from this chromodynamic force is indeed shown to generate a (56,0⁺) + (70,0⁺) mixing of the octet. However, it yields a wrong sign for the mixing angle, thus pointing to a contradiction between spin-spin forces of one-gluon-exchange type and the deep-inelastic structure functions in the valence-quark region. Other spin-spin potentials, giving the right sign for the mixing angle, are shown to be also in difficulty, because of the hyperfine structure of excited levels. Finally, a careful discussion is made of the subtle Σ-Λ effect in both approaches.