Stability of 3D black hole with torsion

Using $N=1+1$ supersymmetric extension of the three-dimensional gravity with torsion, we show that a generic black hole has no exact supersymmetries, the extremal black hole has only one, while the zero-energy black hole has two. Combining these results with the asymptotic supersymmetry algebra, we are naturally led to interpret the zero-energy black hole as the ground state of the Ramond sector, and analogously, the anti-de Sitter solution as the ground state of the Neveau-Schwartz sector.