Direct quark mechanism for weak ΛN <=> NN processes

Two-body weak processes ΛN<=>NN are studied from the viewpoint of quark substructure of baryons. They can be studied in nonmesonic weak decays of hypernuclei and also hyperon production in NN scattering. The direct quark mechanism, in contrast to the one-pion exchange mechanism, is shown to give sizable ΔI=3/2 contribution in the J=0 channel. Nonmesonic decay rates of Λ4H, Λ4He, and Λ5He agree with the current experimental data fairly well. Especially, the n/p ratio is enhanced by the direct quark contribution. The cross sections for pn→Λp scattering are studied in the quark cluster-model approach. (orig.)