Direct quark transition potential for $\Lambda N \to NN$ decay

The weak $\Lambda N\to NN$ transition is studied in the valence quark model approach. The quark component of the two baryon system is described in the quark cluster model and the weak transition potential is calculated by evaluating the matrix elements of the $\Delta S=1$ effective weak Hamiltonian. The transition potential is applied to the decay of hypernuclei and the results are compared with available experimental data. The results indicate that direct quark process is significant and qualitatively different when compared with those in conventional meson-exchange calculations. The direct quark mechanism predicts the violation of the $\Delta I = 1/2$ rule for this transition.