  It may be possible to derive a constituent approximation for bound states in
QCD using hamiltonian light-front field theory. Cutoffs that violate explicit
gauge invariance and Lorentz covariance must be employed. A similarity
renormalization group and coupling coherence are used to compute the effective
hamiltonian as an expansion in powers of the canonical QCD running coupling
constant. At second order the QCD hamiltonian contains a confining interaction,
which is being studied using bound state perturbation theory. Explicit
constituent masses appear because of symmetry violations, and confinement also
produces mass gaps, leading to the possibility of an accurate non-perturbative
constituent approximation emerging in light-front QCD.
