Closed timelike curves in asymmetrically warped brane universes

TL;DR

This paper explores how asymmetrically warped brane universes with two extra dimensions can permit closed timelike curves, potentially challenging causality and enabling experimental tests of the chronology protection conjecture.

Contribution

It presents necessary and sufficient conditions for closed timelike curves in such spacetimes and constructs a specific six-dimensional metric satisfying these conditions while obeying certain energy conditions.

Findings

Existence of closed timelike curves in specific 6D warped metrics.

Conditions on the metric for CTCs are explicitly derived.

Energy conditions are satisfied on the brane, with some violations in the bulk.

Abstract

In asymmetrically warped spacetimes different warp factors are assigned to space and to time. We discuss causality properties of these warped brane universes and argue that scenarios with two extra dimensions may allow for timelike curves which can be closed via paths in the extra-dimensional bulk. In particular, necessary and sufficient conditions on the metric for the existence of closed timelike curves are presented. We find a six-dimensional warped metric which satisfies the CTC conditions, and where the null, weak and dominant energy conditions are satisfied on the brane (although only the former remains satisfied in the bulk). Such scenarios are interesting, since they open the possibility of experimentally testing the chronology protection conjecture by manipulating on our brane initial conditions of gravitons or hypothetical gauge-singlet fermions (sterile neutrinos) which then propagate in the extra dimensions.