Dynamic properties of charmonium

Nonrelativistic quark models of charmonia are tested by comparison of theoretical charmonium decay constants, form factors, and $\ensuremath{\gamma}\ensuremath{\gamma}$ widths with experiment and lattice gauge computations. The importance of relativistic effects, a running coupling, and the correct implementation of bound state effects are demonstrated. We describe how an improved model and computational techniques resolve several outstanding issues in previous nonrelativistic quark models such as the use of ``correction'' factors in quark model form factors, artificial energy prescriptions in decay constant calculations, and ad hoc phase space modifications. We comment on the small experimental value of ${f}_{\ensuremath{\psi}(3S)}$ and the D-wave component of the $J/\ensuremath{\psi}$. Decay constants and $\ensuremath{\gamma}\ensuremath{\gamma}$ widths for bottomonium are also presented.