Decays of Fourth Generation Bound States
  We consider the decay modes of the heavy $q^\prime\bar{q^\prime}$ bound states originating from Higgs boson exchange between quark -- anti-quark pair. In case of a small coupling between the fourth and lower generation the main decay mode is $q^\prime\bar{q^\prime}$ annihilation. We show that for a vector state the dominant decay modes are Higgs-gamma and Higgs-Z decays, while for a pseudoscalar state the strong two-gluon decay mode dominates. The bound states are very narrow. The ratio of the total width to the binding energy is less than 1% if we are not extremely close to the critical quark mass where the binding energy is very small. The discussed decay modes exist for any fermion-antifermion bound states including heavy leptons and heavy neutrinos if their masses are high enough to form a bound state due to attractive Higgs boson exchange potential. 
V. F. Dmitriev and V. V. Flambaum
hep-ph nucl-th