Cylindrically and axially symmetric wormholes. Throats in vacuum?

TL;DR

This review explores the conditions under which cylindrically and axially symmetric wormholes can exist in general relativity, highlighting differences from spherical symmetry and the challenges in finding realistic, asymptotically flat solutions.

Contribution

It provides a comparative analysis of wormhole throat conditions in cylindrical and axial symmetries, including the role of matter, rotation, and vacuum solutions.

Findings

Wormhole throats can exist in static, cylindrically symmetric spacetimes under different conditions than spherical symmetry.

In rotating cylindrical spacetimes, throats may exist with ordinary matter or even in vacuum.

Asymptotically flat wormhole solutions without exotic matter remain elusive.

Abstract

This brief review discusses the existence conditions of wormhole throats and wormholes as global configurations in general relativity under the assumptions of cylindrical and axial symmetries. It is pointed out, in particular, that wormhole throats can exist in static, cylindrically symmetric space-times under slightly different conditions as compared with spherical symmetry. In cylindrical space-time with rotation, throats can exist in the presence of ordinary matter or even in vacuum; however, there are substantial difficulties in obtaining asymptotically flat wormhole configurations without exotic matter: such examples are yet to be found. Some features of interest are discussed in static, axially symmetric configurations, including wormholes with singular rings and wrongly seeming regular wormhole throats in the Zipoy-Voorhees vacuum space-time.