Wave operators on Sobolev spaces

We provide a simple sufficient condition in an abstract framework to deduce the existence and completeness of wave operators (resp. modified wave operators) on Sobolev spaces from the existence and completeness of the usual wave operators (resp. modified wave operators). We then give some examples of Schr"odinger operators to which our abstract result applies. An application to scattering theory for the nonlinear Schr"odinger equation with a potential is also given.