On the existence of star products on quotient spaces of linear   Hamiltonian torus actions
  We discuss BFV deformation quantization of singular symplectic quotient spaces in the special case of linear Hamiltonian torus actions. In particular, we show that the Koszul complex on the moment map of an effective linear Hamiltonian torus action is acyclic. We rephrase the nonpositivity condition of Arms, Gotay and Jennings for linear Hamiltonian torus actions. It follows that reduced spaces of such actions admit continuous star products. 
Hans-Christian Herbig, Srikanth B. Iyengar and Markus J. Pflaum