Hadronic transitions between heavy-quark states in quantum chromodynamics

A general theory is formulated in quantum chromodynamics for hadronic transitions between heavy-quark states. Many predictions follow simply from the tensor properties of the multipoles that dominate in a transition. When a transition involves only soft-pion emission, partial conservation of the axial-vector current provides information on the mass and angular distributions of the pions. Applications to hadronic transitions within the $\Upsilon$ family are presented.