Schwarzschild black hole in closed form [@CHM].

In this paper we examine free quantum electrodynamics in static spherically symmetric spacetimes of arbitrary dimensions in a modified Feynman gauge. (This gauge is closely related to the $A_0=0$ gauge used by Cognola and Lecca [@CL] and reduces to the Feynman gauge in Minkowski spacetime.) Then, we calculate some low energy quantities in electrodynamics outside spherically symmetric black holes. First, we review the calculation of the response rate of a static charge outside the four-dimensional Schwarzschild black hole in the Unruh vacuum [@Unruh]. Next we calculate the low energy absorption cross sections of photons for the Schwarzschild and extreme Reissner-Nordström black holes in arbitrary dimensions higher than three, extending some results obtained by Gubser [@Gubser] using a method [@Teuk; @Staro] based on the Newman-Penrose formalism [@NP].

The paper is organized as follows. In Section \[sec:GuptaBleuler\] we present the mode functions of the electromagnetic field in the spacetime of a spherically symmetric black hole in our modified Feynman gauge. Then we discuss the corresponding quantum theory and show how the Gupta-Bleuler condition (see, e.g., [@IZ]) is implemented to obtain the physical states. In Section \[sec:Coulomb\] we compare the physical modes in the spherical Coulomb 