  A massless scalar field is quantized in the background of a spinning string
with cosmic dislocation. By increasing the spin density toward the dislocation
parameter, a region containing closed timelike curves (CTCs) eventually forms
around the defect. Correspondingly, the propagator tends to the ordinary cosmic
string propagator, leading therefore to a mean-square field fluctuation, which
remains well behaved throughout the process, unlike the vacuum expectation
value of the energy-momentum tensor, which diverges due to a subtle mechanism.
These results suggest that back reaction leads to the formation of a "horizon"
that protects from the appearance of CTCs.
