Quasi-spin-charge separation and the spin quantum Hall effect

We use quantum-field-theory methods to study the network model for the spin quantum Hall transition. When the couplings are fine tuned in a certain way, the spin and charge degrees of freedom, corresponding to the supercurrent algebras su(2)(o) and osp(2\2)(-2), respectively, decouple in the renormalization group flow. The infrared fixed point of this simpler theory is the coset osp(4\4)(1) /su(2)(0) which is closely related to the current algebra osp(2\2)(-2) but not identical. Some critical exponents are computed and shown to agree with the recent predictions based on percolation.