Godel-type Universes in String-inspired Charged Gravity

We consider a string-inspired, gravitational theory of scalar and electromagnetic fields and we investigate the existence of axially-symmetric, Gödel-type cosmological solutions. The neutral case is studied first and an "extreme" Gödel-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 Gödel-type solution for a space-dependent coupling function. Finally, we investigate the existence of Gödel-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.

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