Path integral loop representation of 2+1 lattice non-Abelian gauge theories

A gauge invariant Hamiltonian representation for SU(2) in terms of a spin network basis is introduced. The vectors of the spin network basis are independent and the electric part of the Hamiltonian is diagonal in this representation. The corresponding path integral for SU(2) lattice gauge theory is expressed as a sum over colored surfaces, i.e. only involving the j(p) attached to the lattice plaquettes. These surfaces may be interpreted as the world sheets of the spin networks in 2+1 dimensions; this can be accomplished by working in a lattice dual to a tetrahedral lattice constructed on a face centered cubic Bravais lattice. On such a lattice, the integral of gauge variables over boundaries or singular lines - which now always bound three colored surfaces - only contributes when four singular lines intersect at one vertex and can be explicitly computed producing a 6-j or Racah symbol. We performed a strong coupling expansion for the free energy. The convergence of the series expansions is quite different from the series expansions which were performed in ordinary cubic lattices. Our series seems to be more consistent with the expected linear behavior in the weak coupling limit. Finally, we discuss the connection in the naive continuum limit between this action and that of the B-F topological field theory and also with the pure gravity action. [S0556-2821(98)05914-1].