Hadamard Renormalization of the Stress Energy Tensor in a Spherically   Symmetric Black Hole Space-Time with an Application to Lukewarm Black Holes
  We consider a quantum field which is in a Hartle-Hawking state propagating in a spherically symmetric black hole space-time. We calculate the components of the stress tensor, renormalized using the Hadamard form of the Green's function, in the exterior region of this space-time. We then specialize these results to the case of the `lukewarm' Riessner-Nordstrom-de Sitter black hole. 
Cormac Breen and Adrian C. Ottewill
gr-qc