Closed Timelike Curves in Flat Lorentz Spacetimes
  We consider the region of closed timelike curves (CTC's) in three-dimensional flat Lorentz spacetimes. The interest in this global geometrical feature goes beyond the purely mathematical. Such spacetimes may be considered lower-dimensional toy models of sourceless Einstein gravity or cosmology. In particular, our interest in this note will be to find the set free of CTC's for $E/<\gamma>$, where $E$ is modeled on Minkowski space and $\gamma$ is a Poincar\'e transformation. We describe the set free of CTC's where $\gamma$ is hyperbolic, parabolic and elliptic. 
Virginie Charette, Todd A. Drumm, and Dieter Brill