A Variational Fock-Space Treatment of Quarkonium
  The variational method and the Hamiltonian formalism of QCD are used to derive relativistic, momentum space integral equations for a quark-antiquark system with an arbitrary number of gluons present. As a first step, the resulting infinite chain of coupled equations is solved in the nonrelativistic limit by an approximate decoupling method. Comparison with experiment allows us to fix the quark mass and coupling constant, allowing for the calculation of the spectra of massive systems such as charmonium and bottomonium. Studying the results with and without the nonAbelian terms, we find that the presence of the nonAbelian factors yields better agreement with the experimental spectra. 
L. Di Leo and J. W. Darewych (York University, Toronto, Canada)