Non-Unitary Holography
  We propose gauge theory/gravity duality involving conformal theories based on U(N+k|k) gauge groups. We show that to all orders in 1/N these non-unitary theories based on supergroups are indistinguishable from the corresponding unitary theories where the gauge group is replaced by U(N). This leads to non-unitary gravity duals which to all orders in 1/N are indistinguishable from their unitary cousins. They are distinguished by operators whose correlation functions differ by O(exp(-aN)). The celebrated type IIB on AdS^5 x S^5 and M-theory on AdS^4 x S^7 fall in this class and thus seem to also admit non-unitary non-perturbative completions. It is tempting to conjecture that this setup may provide a non-unitary model for black hole evaporation. 
Cumrun Vafa
hep-th