Period doubling in the 2D Antiferromagnet. New gauge-fields and their   anomalies
  We construct an effective gauge field theory model describing a 2D quantum antiferromagnet in the flux phase ground state. Due to period doubling the number of gauge fields is four rather than the naively expected single one. These additional gauge fields correspond to field configurations in which the flux is staggered, which should be taken into account to enforce single occupancy within the magnetic unit cell. We calculate a new type of quantum anomaly, present in such a model. In particular this leads to a generalized local flux hypothesis, which is tested numerically. 
A.G. Abanov, J.C. Talstra