Adiabatic Theorem in the Case of Continuous Spectra
  In this paper,we present a rigorous demonstration and discussion of the quantum adiabatic theorem for systems having a non degenerate continuous spectrum. A new strategy is initiated by defining a kind of gap, "a virtual gap", for the continuous spectrum through the notion of eigendifferential (Weyl's packet) and using the differential projector operator. Finally we obtain the validity condition of the adiabatic approximation. 
M. Maamache and Y. Saadi