We consider nearly integrable, non-isochronous, a-priori unstable Hamiltonian systems with a (trigonometric polynomial) -perturbation which does not preserve the unperturbed tori. We prove the existence of Arnold diffusion with diffusion time by a variational method which does not require the existence of «transition chains of tori» provided by KAM theory. We also prove that our estimate of the diffusion time is optimal as a consequence of a general stability result proved via classical perturbation theory.
In questa Nota consideriamo sistemi Hamiltoniani quasi-integrabili, non-isocroni, a-priori instabili soggetti ad una perturbazione di ordine (un polinomio trigonometrico) che non preserva i tori imperturbati. Facendo uso di tecniche variazionali che NON richiedono l’esistenza di «catene di tori KAM di transizione», dimostriamo l’esistenza di orbite di diffusione con un tempo di diffusione . Proviamo inoltre che la nostra stima sul tempo di diffusione è ottimale, a seguito di un risultato generale di stabilità per le variabili di azione dimostrato mediante la teoria classica delle perturbazioni.
@article{RLIN_2002_9_13_2_77_0, author = {Massimiliano Berti and Luca Biasco and Philippe Bolle}, title = {Optimal stability and instability results for a class of nearly integrable Hamiltonian systems}, journal = {Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni}, volume = {13}, year = {2002}, pages = {77-84}, zbl = {1072.37060}, mrnumber = {1949480}, language = {en}, url = {http://dml.mathdoc.fr/item/RLIN_2002_9_13_2_77_0} }
Berti, Massimiliano; Biasco, Luca; Bolle, Philippe. Optimal stability and instability results for a class of nearly integrable Hamiltonian systems. Atti della Accademia Nazionale dei Lincei. Classe di Scienze Fisiche, Matematiche e Naturali. Rendiconti Lincei. Matematica e Applicazioni, Tome 13 (2002) pp. 77-84. http://gdmltest.u-ga.fr/item/RLIN_2002_9_13_2_77_0/
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