Discrete torsion, symmetric products and the Hilbert scheme
  We combine our results on symmetric products and second quantization with our description of discrete torsion in order to explain the ring structure of the cohomology of the Hilbert scheme of points on a K3 surface. This is achieved in terms of an essentially unique symmetric group Frobenius algebra twisted by a specific discrete torsion. This twist is realized in form of a tensor product with a twisted group algebra that is defined by a discrete torsion cocycle. We furthermore show that the form of this cocycle is dictated by the geometry of the Hilbert scheme as a resolution of singularities of the symmetric product. 
Ralph M. Kaufmann