  We study a class of supersymmetric spinning particle models derived from the
radial quantization of stationary, spherically symmetric black holes of four
dimensional N= 2 supergravities. By virtue of the c-map, these spinning
particles move in quaternionic Kaehler manifolds. Their spinning degrees of
freedom describe mini-superspace-reduced supergravity fermions. We quantize
these models using BRST detour complex technology. The construction of a
nilpotent BRST charge is achieved by using local (worldline) supersymmetry
ghosts to generating special holonomy transformations. (An interesting
byproduct of the construction is a novel Dirac operator on the superghost
extended Hilbert space.) The resulting quantized models are gauge invariant
field theories with fields equaling sections of special quaternionic vector
bundles. They underly and generalize the quaternionic version of Dolbeault
cohomology discovered by Baston. In fact, Baston's complex is related to the
BPS sector of the models we write down. Our results rely on a calculus of
operators on quaternionic Kaehler manifolds that follows from BRST machinery,
and although directly motivated by black hole physics, can be broadly applied
to any model relying on quaternionic geometry.
