Fidelity Decay for Phase Space Displacements

In this letter we analyse the behavior of fidelity decay under a very specific kind of perturbation: phase space displacements. Under these perturbations, systems will decay following the Lyapunov regime only. Others universal regimes discussed in the literature are not presented in this case; instead, for small values of the perturbation we observe quantum freeze of the fidelity. We also show that it is possible to connect this result with the incoherent neutron scattering problem