FLAVOR-SPIN SYMMETRY AND WEAK DECAYS OF HEAVY HADRONS

Recent developments in the theory of heavy quarks have increased the p rospects for the study of non-perturbative QCD in the weak decays of h eavy mesons and baryons and for the reliable determination of some of the parameters of the Standard Model. It has been made possible due to the discovery of a spin-flavour symmetry for heavy quarks which arise s in QCD when quark mass is taken to infinity. Certain properties in h adrons containing a heavy quark then become independent of its mass an d spin. These ideas have tremendous impact on the phenemenology of hea vy hadrons. In particular, these symmetries give rise to restrictive r elations among weak decay amplitudes and reduce the number of independ ent form factors. By relating various matrix elements and fixing norma lization of some matrix elements, the heavy quark symmetry has enhance d our predictive ability, allowing in some cases to bypass the difficu lties of understanding hadronic structure.