Warped AdS_3 Black Holes

Three dimensional topologically massive gravity (TMG) with a negative cosmological constant -ell^{-2} and positive Newton constant G admits an AdS_3 vacuum solution for any value of the graviton mass mu. These are all known to be perturbatively unstable except at the recently explored chiral point muell=1. However we show herein that for every value of muell< 3 there are two other (potentially stable) vacuum solutions given by SL(2,R)x U(1)-invariant warped AdS_3 geometries, with a timelike or spacelike U(1) isometry. Critical behavior occurs at muell=3, where the warping transitions from a stretching to a squashing, and there are a pair of warped solutions with a null U(1) isometry. For muell>3, there are known warped black hole solutions which are asymptotic to warped AdS_3. We show that these black holes are discrete quotients of warped AdS_3 just as BTZ black holes are discrete quotients of ordinary AdS_3. Moreover new solutions of this type, relevant to any theory with warped AdS_3 solutions, are exhibited. Finally we note that the black hole thermodynamics is consistent with the hypothesis that, for muell>3, the warped AdS_3 ground state of TMG is holographically dual to a 2D boundary CFT with central charges c_R={15(muell)^2+81over Gmu((muell)^2+27)} and c_L={12 muell^2over G((muell)^2+27)}.