 0593 Marian Gidea, Rafael de la Llave
 Topological methods in the instability problem of Hamiltonian systems
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Mar 7, 05

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Abstract. We use topological methods to investigate some recently proposed
mechanisms of instability (Arnol'd diffusion) in Hamiltonian
systems.
In these mechanisms, chains of heteroclinic connections between
whiskered tori are constructed, based on the existence of a
normally hyperbolic manifold $\Lambda$, so that: (a) the manifold
$\Lambda$ is covered rather densely by transitive tori (possibly
of different topology), (b) the manifolds $W^\st_\Lambda$,
$W^\un_\Lambda$ intersect transversally, (c) the systems satisfies
some explicit nondegeneracy assumptions, which hold generically.
In this paper we use the method of correctly aligned windows to
show that, under the assumptions (a), (b) (c), there are orbits
that move a significant amount.
As a matter of fact, the method presented here does not require
that the tori are exactly invariant, only that they are
approximately invariant. Hence, compared with the previous
papers, we do not need to use KAM theory. This lowers the
assumptions on differentiability.
Also, the method presented here allows to produce concrete estimates on the time to move, which were not considered in the previous papers.
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