Phenomenological study of two-gluon densities
  The decay of colour neutral 2-gluon systems in qqbar and 2q2qbar has been simulated with the Monte-Carlo method, taking into account an effective 1-gluon exchange interaction between the emitted quarks, which was folded with a 2-gluon density determined self-consistently. Finite 2-gluon densities were obtained with a mean square radius <r^2> of about 0.5 fm^2. These give a significant contribution to the 2-gluon field correlators and the gluon propagator from lattice QCD. By solving a relativistic Schroedinger equation the binding potential of the 2-gluon density is computed. By the relation 2g->(qqbar)^n this corresponds to the confinement potential between quarks, which is in excellent agreement with the confinement potential from lattice QCD. The lowest bound state in this potential allows an interpretation of the 2-gluon mass as binding energy of the two gluons. The lowest glueball with Eo=0.68+-0.10 GeV is in the mass region of the scalar sigma(550), with a mass significantly lower then obtained in lattice QCD simulations. However, the first and second radial excitations agree with the lattice results. 
H. P. Morsch, P. Zupranski