String States on AdS_3 x S^3 from the Supergroup
  In the hybrid formulation of string theory on AdS_3 x S^3, the compactification-independent physical spectrum at the first massive level is determined. We find that these states transform in representations of the Lie superalgebra psl(2|2) and present a cohomological characterisation of them within the context of the PSL(2|2) WZW model. We conjecture that a similar cohomological description of the physical states also exists at higher mass levels and give partial evidence for this by comparing our results to the RNS string spectrum. 
Sebastian Gerigk
hep-th