Phenomenological potentials for QCD order parameters

We discuss an effective potential for QCD from a phenomenological point of view. The potential is expressed in terms of order parameters of the gluon and chiral condensates and a scale is set by using the value of 〈vac‖:(${\alpha }_s$/π)$G_{\mu \nu }^a$(0)$G_a$μν(0):‖vac〉 obtained from QCD sum-rule studies. We point out that in the case of nontopological soliton model of hadrons, the quantity which plays the role of the ‘‘bag constant’’ is not a renormalization-group invariant and therefore should not be identified with the energy density of the vacuum. Our model also provides a simple characterization of the mass matrix coupling scalar gluonium and scalar quarkonium. Further, the structure of the model is such that the dependence of the condensate order parameters on temperature and baryon density (as determined in lattice-gauge studies) may be readily parametrized. We also discuss the results of certain nuclear-physics experiments in terms of the dependence of QCD order parameters on baryon density.