Pair creation rate for U(1${)}^2$ black holes

I consider a truncation of low-energy string theory which contains two U(1) gauge fields. After making some general comments on the theory, I describe a previously obtained instanton for the pair creation of black holes when both gauge fields are nonzero, and obtain the pair creation rate by calculating its action. This calculation agrees qualitatively with the earlier calculation of the pair creation rate for black holes in Einstein-Maxwell theory. That is, the pair creation is strongly suppressed in realizable circumstances, and it reduces to the Schwinger result in the point-particle limit. The pair creation of nonextreme black holes is enhanced over that of extreme black holes by ${\mathit{e}}_{\mathrm{BH}}^{\mathit{s}\mathit{c}\mathit{r}\mathit{A}}$/4. © 1995 The American Physical Society.