Milanesi, GiuseppeO'Loughlin, Martin20052011-09-0720052011-09-072005JHEP 0509 (2005) 008https://openscience.sissa.it/handle/1963/1738We study in detail the moduli space of solutions discovered in LLM relaxing the constraint that guarantees the absence of singularities. The solutions fall into three classes, non-singular, null-singular and time machines with a time-like naked singularity. We study the general features of these metrics and prove that there are actually just two generic classes of space-times - those with null singularities are in the same class as the non-singular metrics. AdS/CFT seems to provide a dual description only for the first of these two types of space-time in terms of a unitary CFT indicating the possible existence of a chronology protection mechanism for this class of geometries.374570 bytesapplication/pdfen-USPreprint