QCD on a Tree
  A model is proposed which can be regarded as a mean field approximation for pure lattice QCD and chiral field. It always possesses a phase transition between a strong coupling phase (where it reduces to a one-plaquette integral) and a non-trivial weak coupling one. For the U(N) gauge group, it is equivalent to some multi-matrix model. This analogy allows for determining possible large N critical regimes thus generalizing the Gross-Witten phase transition in the one-plaquetee model. 
D.V.Boulatov