  We study aspects of the propagation of strings on BTZ black holes. After
performing a careful analysis of the global spacetime structure of generic BTZ
black holes, and its relation to the geometry of the SL(2,R) group manifold, we
focus on the simplest case of the massless BTZ black hole. We study the SL(2,R)
Wess-Zumino-Witten model in the worldsheet minisuperspace limit, taking into
account special features associated to the Lorentzian signature of spacetime.
We analyse the two- and three-point functions in the pointparticle limit. To
lay bare the underlying group structure of the correlation functions, we derive
new results on Clebsch-Gordan coefficients for SL(2,R) in a parabolic basis. We
comment on the application of our results to string theory in singular
time-dependent orbifolds, and to a Lorentzian version of the AdS/CFT
correspondence.
