Godel-type universes in string-inspired charged gravity - art. no. 103519

We consider a string-inspired, gravitational theory of scalar and electroma gnetic fields and eve investigate the existence of axially symmetric, Godel -type cosmological solutions. The neutral ease is studied first and an "ext reme" Godel-type rotating solution, which respects the causality, is determ ined. The charged case is considered next and two new configurations, minim ally coupled to gravity, are presented, for the electromagnetic field. Anot her configuration motivated by the expected distribution of currents and ch arges in a rotating universe is studied and shown to lead to a Godel-type s olution for a space-dependent coupling function. Finally, we investigate th e existence of Godel-type cosmological solutions in the framework of the on e-loop corrected superstring effective action and we determine the sole con figuration of the electromagnetic field that leads to such a solution. It t urns out that, in all the charged cases considered, closed timelike curves do appear and the causality is always violated. [S0556-2821(99)06920-9].