Godel-type Universes in String-inspired Charged Gravity

TL;DR

This paper explores G"odel-type cosmological solutions within a string-inspired gravity framework, analyzing neutral and charged cases, and finds that all charged solutions exhibit causality violations due to Closed Timelike Curves.

Contribution

It introduces new G"odel-type solutions in string-inspired gravity with electromagnetic fields, including space-dependent couplings and one-loop corrections, highlighting causality violations.

Findings

Neutral G"odel-type solution respects causality.

Charged solutions exhibit Closed Timelike Curves.

String-inspired models lead to causality violations.

Abstract

We consider a string-inspired, gravitational theory of scalar and electromagnetic fields and we investigate the existence of axially-symmetric, G\"{o}del-type cosmological solutions. The neutral case is studied first and an "extreme" G\"{o}del-type rotating solution, that respects the causality, is determined. The charged case is considered next and two new configurations for the, minimally-coupled to gravity, electromagnetic field are presented. Another configuration motivated by the expected distribution of currents and charges in a rotating universe is studied and shown to lead to a G\"{o}del-type solution for a space-dependent coupling function. Finally, we investigate the existence of G\"{o}del-type cosmological solutions in the framework of the one-loop corrected superstring effective action and we determine the sole configuration of the electromagnetic field that leads to such a solution. It turns out that, in all the charged cases considered, Closed Timelike Curves do appear and the causality is always violated.