Large N limit of Extremal Non-supersymmetric Black Holes
  The large N limit of extremal non-supersymmetric Type-I five-dimensional string black holes is studied from the point of view of D-branes.   We find that the agreement between the D-brane and the black-hole picture is due to an asymptotic restoration of supersymmetry in the large $N$ limit in which both pictures are compared.   In that limit Type-I string perturbation theory is effectively embedded into a Type-IIB perturbation theory with unbroken supersymmetric charges whose presence guarantees the non-renormalization of mass and entropy as the effective couplings are increased. In this vein, we also study the near-horizon geometry of the Type-I black hole using D5-brane probes to find that the low energy effective action for the probe is identical to the corresponding one in the auxiliary Type-IIB theory in the large N limit. 
J.L.F. Barbon, J. Manes and M.A. Vazquez-Mozo