Modified spinning black holes
  In the context of f(R) modified gravity theories we determine that the black holes existence is determined by the sign of a parameter dependent of the mass, the charge, the spin and the scalar curvature. We obtain the different astrophysical objects derived from the presence of different horizons. Thermodynamics for this kind of black holes is studied for negative values of the curvature, revealing that we can distinguish between two kinds of BH: fast and slow. 
J. A. R. Cembranos, A. de la Cruz-Dombriz, P. Jimeno Romero
gr-qc hep-th