Semiclassical backreaction around a nearly spinning cosmic string

TL;DR

This study explores how quantum scalar fields influence the spacetime around a nearly spinning cosmic string, revealing an expanding ergoregion that may protect against causality violations.

Contribution

It provides the first analysis of semiclassical backreaction effects on a nearly spinning cosmic string, linking ergoregion formation to chronology protection mechanisms.

Findings

Ergoregion spreads indefinitely as spin approaches dislocation parameter

Closed timelike curves appear when spin exceeds dislocation parameter

Ergoregion formation may prevent causality violations in related geometries

Abstract

This paper 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.