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Published online by Cambridge University Press: 30 September 2008
An unambiguous physical definition of creatable universes was recently proposed.According to it, flat and closed Friedmann-Robertson-Walker (FRW) backgrounds can be created as quantum vacuum fluctuations, whereas open backgrounds are not creatable. Here, physically motivated perturbations of closed and flat backgrounds are analyzed. Various creatable perturbed FRW universes are thusfound. Some of them involve scalar and tensor perturbations with appropriatespectra, whereas other ones are Bianchi models.