Heavy-quark spectroscopy for effective-action models

Results are reported for an application of the effective-action method to the computation of spectra for $c\bar{c}$, $b\bar{b}$, and $t\bar{t}$ systems. The method determines static potentials from models for the vacuum dielectric permeability, of which two are considered: the leading-logarithm model and a hard-bag model. The spectra are then computed with standard nonrelativistic techniques. A new value of the leading-logarithm-model parameter $\kappa$ is obtained from a fit to $b\bar{b}$ data; it corresponds to a value of 161 MeV for ${\Lambda }_{\overline{\mathrm{MS}}}$, the scale mass of quantum chromodynamics ($\overline{\mathrm{MS}}$ denotes the modified minimal-subtraction scheme).