  A constituent parton picture of hadrons with logarithmic confinement arises
naturally in light-front QCD when the hamiltonian is computed using a
perturbative renormalization group; however, rotational symmetry is not
manifest as a simple kinematic symmetry. Relevant operators must typically be
fine-tuned when a perturbative renormalization group is used, and in
light-front field theory such operators contain functions of longitudinal
momenta. We explore the possibility that a gluon mass operator with simple
longitudinal momentum dependence may improve approximate kinematic rotational
symmetry, as revealed by the potential between heavy quarks.
