Light-front Hamiltonians for heavy quarks and gluons

Light front (LF) Hamiltonian operators for effective particles in quantum field theory (QFT) provide a new path toward understanding of hadronic structure and interactions. The origin of new thrust is a far reaching simplification of the approach in comparison to the standard form of dynamics: boosts are kinematical, instantaneous potentials can exist on the front hyperplane without contradicting the assumption that no physical effect can propagate faster than light, and one can avoid the problem of the vacuum structure. Rotational symmetry is dynamical and poses problems, but we have a lot of intuition about rotational symmetry. It seems simpler to obtain rotational symmetry in the LF Hamiltonian approach than to solve the problem of dynamical boost symmetry or the vacuum problem in the standard approach. The price one has to pay for these gains in the LF Hamiltonian approach is a heavy-duty renormalization group procedure and a scheme to finesse a leading approximation around which one can develop a calculation of corrections. I describe a heuristic picture of binding for heavy quarks and gluons that begins to emerge from application of these tools in QCD. I will focus on results for gluonium and heavy quarkonia. The binding of quarks and gluons occurs typically above threshold, which means that the sum of masses of the constituents is smaller than the mass of the bound state. How can such effect occur in a relativistic quantum theory? It does not happen in QED. So, how can it happen? A boost-invariant light-front Hamiltonian formula-