Semiclassical backreaction around a nearly spinning cosmic string

AbstractThis Letter investigates semiclassical backreaction of a conformally coupled massless scalar field on the geometrical background of a nearly spinning cosmic string — the spin density is smaller than, but arbitrarily close to, the dislocation parameter. As the spin density approaches the dislocation parameter, it is shown that an ergoregion spreads indefinitely around the cosmic string, boosting along the string axis the once static observers. Considering that the geometrical background contains closed timelike curves when the spin density exceeds the dislocation parameter, it is argued that the appearance of the ergoregion may be part of a chronology protection mechanism that takes place in related non-stationary geometries