Paper detail

Normal forms for perturbations of systems possessing a Diophantine invariant torus

In 1967 Moser proved the existence of a normal form for real analytic perturbations of vector fields possessing a reducible Diophantine invariant quasi-periodic torus. In this paper we present a proof of existence of this normal form based on an abstract inverse function theorem in analytic class. The given geometrization of the proof can be opportunely adapted accordingly to the specificity of systems under study. In this more conceptual frame, it becomes natural to show the existence of new remarkable normal forms, and provide several translated-torus theorems or twisted-torus theorems for systems issued from dissipative generalizations of Hamiltonian Mechanics, thus providing generalizations of celebrated theorems of Herman and Rüssmann, with applications to Celestial Mechanics.