The Relativistic Bound State Problem in QCD: Transverse Lattice Methods

The formalism for describing hadrons using a light-cone Hamiltonian of SU(N) gauge theory on a coarse transverse lattice is reviewed. Physical gauge degrees of freedom are represented by disordered flux fields on the links of the lattice. A renormalised light-cone Hamiltonian is obtained by making a colour-dielectric expansion for the link-field interactions. Parameters in the Hamiltonian are renormalised non-perturbatively by seeking regions in parameter space with enhanced Lorentz symmetry. In the case of pure gauge theories to lowest non-trivial order of the colour-dielectric expansion, this is sufficient to determine accurately all parameters in the large-N limit. We summarize results from applications to glueballs. After quarks are added, the Hamiltonian and Hilbert space are expanded in both dynamical fermion and link fields. Lorentz and chiral symmetry are not sufficient to accurately determine all parameters to lowest non-trivial order of these expansions. However, Lorentz symmetry and one phenomenological input, a chiral symmetry breaking scale, are enough to fix all parameters unambiguously. Applications to lightlight and heavy-light mesons are described.