Roles of Quarks in Strong and Weak YN Interactions

The short range parts of the strong and weak hyperon-nucleon interactions are studied with quark substructure of the baryons taken into account. A summary of the quark cluster model calculations of the baryon-baryon interactions is presented. It is pointed out that the spin-flavor symmetry structure determines the qualitative behaviors of the short-range YN interactions. We also show that the spin-orbit YN forces give characteristic behaviors, which are distinct from the meson exchange forces. Weak decays of $\Lambda$ in hypernuclei are described by the direct quark mechanism. We find that the neutron induced nonmesonic decay is enhanced due to the direct quark transition. Importance of the $\Delta I=3/2$ decay amplitudes is emphasized both for the nonmesonic weak decays and the $\pi^+$ emission in the $\Lambda$ decay.