gauge [@CHM] with the ones obtained in the modified Feynman gauge. In Section \[sec:Rate\] we review the calculation of the response rate of a static charge outside a four-dimensional Schwarzschild black hole. In Sections \[sec:Schwarz\] and \[sec:Reissner\] we present the photon absorption cross sections by the Schwarzschild and extreme Reissner-Nordström black holes of arbitrary dimensions higher than three. In Sec. \[sec:Conclusions\] we summarize the main results and make some remarks. In Appendix \[app:Mink\] we compute some components of field-strength two-point function in Minkowski spacetime using spherical polar coordinates and show that they agree with those obtained using Cartesian coordinates. In Appendix \[app:Formula\] a summation formula for Legendre functions used in Section \[sec:Rate\] is derived. In Appendix \[app:Cross\], a formula which relates the absorption [*probability*]{} to the absorption [*cross section*]{} is derived in arbitrary dimensions. We use the metric signature $(+--\cdots-)$ and the natural units with $G=\hbar=c=1$ throughout this paper.

Gupta-Bleuler quantization in a modified Feynman gauge {#sec:GuptaBleuler}
======================================================

In this section we analyze the field equations for the electromagnetic field in spherically symmetric and static spacetimes in a modified Feynman gauge. Then we discuss the Gupta-Bleuler quantization in this gauge.

The line element of the spacetime we study is $$d\tau^2 