Factor ordering problem in stochastic inflation - art. no. 123506

The stochastic approach to inflation suffers from ambiguities due to the ar bitrary choice of the time variable and due to the choice of the factor ord ering in the corresponding Fokker-Planck equation. Here it is shown that bo th ambiguities can be removed if we require that the factor ordering should be set in such a way that physical results are invariant with respect to t ime reparametrizations. This requirement uniquely selects the so-called Ito factor ordering. Additional ambiguities associated with non-trivial kineti c terms of the scalar fields are also discussed, as well as ways of constra ining these ambiguities. [S0556-2821(99)08212-0].