  At the Large Hadron Collider, heavy particles may be produced in pairs close
to their kinematic threshold. If these particles have strong enough attractive
interactions they may form bound states. Consequently, the bound states may
decay through annihilation back into the standard model. Such annihilation
decays have the potential to provide much information about the bound
particles, such as their mass, spin, or charges, in a manner completely
complementary to standard single particle cascade decays. Many of the
signatures, such as dijet resonances, will be challenging to find, but may be
extremely helpful in unraveling the nature of the new physics. In the standard
model, the only novel annihilation decays would be for toponium; these will be
hard to see because of the relatively large width of the top quark itself. In
models with supersymmetry, marginally visible annihilation decays may occur for
example, from bound states of gluinos to dijets or tops. If new particles are
bound through forces stronger than QCD, annihilation decays may even be the
discovery mode for new physics. This paper presents various theoretical results
about bound states and then addresses the practical question of whether any of
their annihilation decays can be seen at the LHC.
