Perturbative and non-perturbative N=8 supergravity

We study extremal black holes, their ADM mass and area of the horizon in N = 8 supergravity. Contrary to intuition gained from N = 2,3, 4 theories, in N = 8, as well as in N = 5,6, supergravity BPS states may become massless only at the boundary of moduli space. We show that stringy states described in Green, Ooguri, Schwarz (2007) [10], which have no mass gap and survive in toroidal compactifications in addition to the massless states of perturbative N = 8 supergravity, display a null singularity in four-dimensional space-time, when viewed as solutions of the N = 8 version of Einstein equations. We analyze known methods of resolving such singularities and explain why they all fail in D = 4, N = 8 supergravity. We discuss possible implications for the issue of UV finiteness of perturbative N = 8 supergravity and the plausibility of a non-perturbative completion that exclude singular states. (c) 2010 Published by Elsevier B.V.