Quantum backreaction for overspinning BTZ geometries

We examine the semiclassical backreaction of a conformally coupled scalar field on an overspinning (Bañados-Teitelboim-Zanelli) BTZ geometry. This extends the work done on a similar problem for (2+1)-anti-de Sitter geometries of the BTZ family with |M|>|J|. The overspinning classical solutions correspond to |M|<|J| and possess a naked singularity at r=0. Using the renormalized quantum stress-energy tensor for a conformally coupled scalar field on such a spacetime, we obtain the semiclassical Einstein equations, which we attempt to solve perturbatively. We show that the stress-energy tensor is nonrenormalizable in this approach, and consequently the perturbative solution to the semiclassical equations in the overspinning case does not exist. This could be an indication of the fact that the naked singularity at the center of an overspinning geometry is of a more severe nature than the conical singularity found in the same family of BTZ geometries.