In Xiao-Gang Wen's review of topological order http://arxiv.org/abs/1210.1281 , he states in footnote 52 that string-nets are so far unable to produce the chiral coupling between the SU(2) gauge boson and the fermions. Is it known how this chiral coupling can be expressed in lattice gauge theory, and the remaining question is one of emergence; or is it the case that its expression in lattice gauge theory is unknown, analogous to the chiral fermion question which took many years to solve?
The chiral-fermion/chiral-gauge-theory problem is solved: any anomaly-free chiral gauge theories can be put on lattice by simply turning on a proper interaction. See my new papers http://arxiv.org/abs/1305.1045 and http://arxiv.org/abs/1303.1803
As a result, the string-net theory can also produce the coupling between the SU(2) gauge boson and the chiral fermions.