Lessons from Schwinger Effective Action for Black Holes
  We revisit the Hawking radiation by comparing the effective actions in the in-out formalism, and advance an interpretation of the vacuum polarization and the Hawking radiation. The equivalence exists between the spinor QED effective action in a constant electric field and the nonperturbative effective action of a massless boson on the horizon of a Schwarzschild black hole. 
Sang Pyo Kim (Kunsan Nat'l Univ.)
hep-th gr-qc hep-ph