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A generic Banados-Teitelboim-Zanelli (BTZ) black hole has a region behind its inner horizon
which includes closed time like curves. This region, which contains a part of the causal boundary
of the underlying 3D Anti de Sitter (AdS3), is cut out of the geometry, rendering the geometry
geodesically incomplete. Moreover, it has been shown that components of the energy momentum
tensor associated with quantum ?uctuations of an arbitrary ?eld in a generic BTZ background blows
up at the inner horizon. Here we construct a new class of solutions to AdS3 Einstein gravity, the
\folded-BTZ" black holes, which does not have these problems. Folded-BTZ black holes have the
same geometry as BTZ outside the outer horizon but do not have the inner horizon and the region
behind it, and are hence speci?ed by two quantum numbers, their mass and angular momentum.
Folded-BTZ black holes are supported by an \instantonic string", a gravitational instanton, located
in the middle of the region between the two horizons and may be constructed through ordinary BTZ
procedure [1] applied to an AdS3 with the instantonic string in the background.
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