Supersymmetry, attractors and cosmic censorship

We show that requiring unbroken supersymmetry everywhere in black-hole-type solutions of N = 2, d = 4 supergravity coupled to vector supermultiplets ensures in most cases absence of naked singularities. We formulate three specific conditions which we argue are equivalent to the requirement of global supersymmetry. These three conditions can be related to the absence of sources for NUT charge, angular momentum, scalar hair and negative energy, although the solutions can still have globally defined angular momentum and non-trivial scalar fields, as we show in an explicit example. Furthermore, only the solutions satisfying these requirements seem to have a microscopic interpretation in string theory since only they have supersymmetric sources. These conditions exclude, for instance, singular solutions such as the Kerr-Newman with M = vertical bar q vertical bar, which fails to be everywhere supersymmetric. We also present a re-derivation of several results concerning attractors; in N = 2, d = 4 theories based on the explicit knowledge of the most general solutions in the timelike class. (C) 2006 Elsevier B.V. All rights reserved.