Implications of duality, unitarity and SU₆ symmetry for baryons and baryonium

It is shown that there exists a limit, involving both an exactly SU₆ symmetric spectrum and exactly exchange degenerate Regge trajectories, in which the OZI like selection rule for baryonium is exact. Deviations from the rule occur when SU₆ is broken and when unitarity forces the breaking of exchange degeneracy. By combining both of these latter effects we can qualitatively account for the observed pattern of broken exchange degeneracy among baryons. The strength of the baryonium coupling to mesons is related to the breaking of exchange degeneracy.