[codethief]

From the paper:

> Finally, we stress again that our main results are valid in an arbitrary background spacetime (including charged Kerr black holes [51, section 12.3]), provided that the CTC of interest is the orbit of a periodic one-parameter family of symmetries of the metric. This happens in all axisymmetric models whose rotation Killing field becomes timelike somewhere.

[ben_w]

Thanks, that's what I get for skim-reading :)