Universailty of Low Energy Absorption Cross-sections for Black Holes
  In this paper we compute the low energy absorption cross-section for minimally coupled massles scalars and spin-$1/2$ particles, into a general spherically symmetric black hole in arbitrary dimensions. The scalars have a cross section equal to the area of the black hole, while the spin-$1/2$ particles give the area measured in a flat spatial metric conformally related to the true metric. 
Sumit R. Das, Gary Gibbons and Samir D. Mathur