Nonleptonic weak decays of hyperon and hypernuclei

The weak ΛN → NN transition is studied in the valence quark model approach. The two baryon system is described in the quark cluster model and the weak transition amplitude is calculated by evaluating the matrix elements of the effective weak ΔS=1 hamiltonian. The results indicate some qualitative differences when compared with those in conventional meson-exchange calculations. Especially, we conclude that contributions of the ΔI=3/2 transition are significant and that the discrepancy in the n-p ratio between theory and experiment could be resolved by including the direct-quark processes. ((orig.))