Gauge-invariant multipole expansion scheme for heavy-quark systems in quantum chromodynamics

Separation of short-distance and long-distance dynamics for heavy-quark--antiquark systems interacting with color gluons is investigated through a classification of gluons according to their ranges. A gauge-invariant double multipole expansion scheme is constructed which takes into account color fluctuation of heavy-quark systems. Hadronic transitions between heavy-quark--antiquark bound states as well as the static quark-antiquark potential are studied within this framework