Stability of Picard operators under operator perturbations

Stability of wave-packet dynamics under perturbations.

We introduce a method to investigate the stability of wave-packet dynamics under perturbations of the Hamiltonian. Our approach relies on semiclassical approximations, but is nonperturbative. Two separate contributions to the quantum fidelity are identified: one factor derives from the dispersion of the wave packets, whereas the other factor is determined by the separation of a trajectory of th...

Preservation of the Range under Perturbations of an Operator

A sufficient condition for the stability of the range of a positive operator in a Hilbert space is given. As a consequence, we get a class of additive perturbations which preserve regularity of the critical point 0 of a positive operator in a Krein space.

The Behavior of Functions of Operators under Perturbations

This is a survey article. We consider different problems in connection with the behavior of functions of operators under perturbations of operators. We deal with three classes of operators: unitary operators, self-adjoint operators, and contractions. We study operator Lipschitz and operator differentiable functions. We also study the behavior of functions under perturbations of an operator by a...

A renormalization operator for 1D maps under quasi-periodic perturbations

This paper concerns with the reducibility loss of (periodic) invariant curves of quasi-periodically forced one dimensional maps and its relationship with the renormalization operator. Let gα be a one-parametric family of one dimensional maps with a cascade of period doubling bifurcations. Between each of these bifurcations, there exists a parameter value αn such that gαn has a superstable perio...

Perturbations of Operators, Ii