%0 Journal Article %J J. Math. Pures Appl. 82 (2003) 613-664 %D 2003 %T Drift in phase space: a new variational mechanism with optimal diffusion time %A Massimiliano Berti %A Luca Biasco %A Philippe Bolle %X 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 ``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. %B J. Math. Pures Appl. 82 (2003) 613-664 %I Elsevier %G en_US %U http://hdl.handle.net/1963/3020 %1 1313 %2 Mathematics %3 Functional Analysis and Applications %$ Submitted by Andrea Wehrenfennig (andreaw@sissa.it) on 2008-10-02T15:07:59Z\\nNo. of bitstreams: 1\\n0205307v1.pdf: 505505 bytes, checksum: 2dab01ff574df56912b2fe8d3c56108a (MD5) %R 10.1016/S0021-7824(03)00032-1