Strings in the Extended BTZ Spacetime
  We study string theory on the extended spacetime of the BTZ black hole, as described by an orbifold of the SL(2,R) WZW model. The full spacetime has an infinite number of disconnected boundary components, each corresponding to a dual CFT. We discuss the computation of bulk and boundary correlation functions for operators inserted on different components. String theory correlation functions are obtained by analytic continuation from an orbifold of the SL(2,C)/SU(2) coset model. This yields two-point functions for general operators, including those describing strings that wind around the horizon of the black hole. 
Samuli Hemming, Esko Keski-Vakkuri, and Per Kraus