@article {2003,
	title = {Drift in phase space: a new variational mechanism with optimal diffusion time},
	journal = {J. Math. Pures Appl. 82 (2003) 613-664},
	number = {arXiv.org;math/0205307v1},
	year = {2003},
	publisher = {Elsevier},
	abstract = {We consider non-isochronous, nearly integrable, a-priori unstable Hamiltonian systems with a (trigonometric polynomial) $O(\\\\mu)$-perturbation which does not preserve the unperturbed tori. We prove the existence of Arnold diffusion with diffusion time $ T_d = O((1/ \\\\mu) \\\\log (1/ \\\\mu))$ by a variational method which does not require the existence of {\textquoteleft}{\textquoteleft}transition chains of tori\\\'\\\' provided by KAM theory. We also prove that our estimate of the diffusion time $T_d $ is optimal as a consequence of a general stability result derived from classical perturbation theory.},
	doi = {10.1016/S0021-7824(03)00032-1},
	url = {http://hdl.handle.net/1963/3020},
	author = {Massimiliano Berti and Luca Biasco and Philippe Bolle}
}
