No black-hole theorem in three-dimensional gravity
A common property of known black-hole solutions in (2+1)-dimensional gravity is that they require a negative cosmological constant. To explain this, it is shown in this Letter that a (2+1)-dimensional gravity theory which satisfies the dominant energy condition forbids the existence of a black hole.
Ida
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Department of Physics, Kyoto University, Kyoto 606-8502, Japan.