Dynamical Zero Modes and Pure Glue ${\bf{\rm{QCD}}_{1+1}}$ in Light-Cone   Field Theory
  We consider light-cone quantized ${\rm{QCD}}_{1+1}$ on a `cylinder' with periodic boundary conditions on the gluon fields. This is the framework of discretized light-cone quantization. We review the argument that the light-cone gauge $A^+=0$ is not attainable. The zero mode is a dynamical and gauge invariant field. The attainable gauge has a Gribov ambiguity. We exactly solve the problem of pure glue theory coupled to some zero mode external sources. We verify the identity of the front and the more familiar instant form approaches. We obtain a discrete spectrum of vacuum states and their wavefunctions. 
Alex C. Kalloniatis, Hans-Christian Pauli and Stephen Pinsky