Remarks on Schwinger Pair Production by Charged Black Holes
  We introduce a canonical method for pair production by electromagnetic fields. The canonical method in the space-dependent gauge provides pair-production rate even for inhomogeneous fields. Further, the instanton action including all corrections leads to an accurate formula for the pair-production rate. We discuss various aspects of the canonical method and clarify terminology for pair production. We study pair production by charged black holes first by finding states of the field equation that describe pair production and then by applying the canonical method. 
Sang Pyo Kim (Kunsan Nat'l Univ.), Don N. Page (Univ. Alberta)