On the existence of inequivalent quasideterministic domains

In the framework of the history approach to quantum mechanics and, in particular, of the formulation of Gell-Mann and Hartle, the question of the existence of inequivalent decoherent sets of histories is reconsidered. A simple but acceptably realistic model of the dynamics of the universe is proposed and a particular set of histories is shown to be decoherent. By suitable tranformations of this set, a family of sets of histories is then generated, such that the sets, first, are decoherent on the basis of the assumed dynamics of the universe and, secondly, arc certainly inequivalent, apart from trivial special cases. Finally, the original set of histories is refined to get a model of the usual quasiclassical domain and it is shown that, applying to it the previously considered transformations, a family of sets of histories is obtained which share typical properties of the usual quasiclassical domain.Supported in part by the Ministero dell'Università e della Ricerca Scientifica e Tecnologica and by the Istituto Nazionale di Fisica Nucleare.