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2013
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# Marco Sansottera

via Saldini 50, 20133, Milano, Italy
Dipartimento di Matematica, Università degli Studi di Milano

## Publications:

 Bambusi D., Fusè A., Sansottera M. Exponential Stability in the Perturbed Central Force Problem 2018, vol. 23, no. 7-8, pp.  821-841 Abstract We consider the spatial central force problem with a real analytic potential. We prove that for all analytic potentials, but for the Keplerian and the harmonic ones, the Hamiltonian fulfills a nondegeneracy property needed for the applicability of Nekhoroshev’s theorem. We deduce stability of the actions over exponentially long times when the system is subject to an arbitrary analytic perturbation. The case where the central system is put in interaction with a slow system is also studied and stability over exponentially long time is proved. Keywords: exponential stability, Nekhoroshev theory, perturbation theory, normal form theory, central force problem Citation: Bambusi D., Fusè A., Sansottera M.,  Exponential Stability in the Perturbed Central Force Problem, Regular and Chaotic Dynamics, 2018, vol. 23, no. 7-8, pp. 821-841 DOI:10.1134/S156035471807002X
 Giorgilli A., Locatelli U., Sansottera M. Secular Dynamics of a Planar Model of the Sun-Jupiter-Saturn-Uranus System; Effective Stability in the Light of Kolmogorov and Nekhoroshev Theories 2017, vol. 22, no. 1, pp.  54-77 Abstract We investigate the long-time stability of the Sun-Jupiter-Saturn-Uranus system by considering a planar secular model, which can be regarded as a major refinement of the approach first introduced by Lagrange. Indeed, concerning the planetary orbital revolutions, we improve the classical circular approximation by replacing it with a solution that is invariant up to order two in the masses; therefore, we investigate the stability of the secular system for rather small values of the eccentricities. First, we explicitly construct a Kolmogorov normal form to find an invariant KAM torus which approximates very well the secular orbits. Finally, we adapt the approach that underlies the analytic part of Nekhoroshev’s theorem to show that there is a neighborhood of that torus for which the estimated stability time is larger than the lifetime of the Solar System. The size of such a neighborhood, compared with the uncertainties of the astronomical observations, is about ten times smaller. Keywords: $n$-body planetary problem, KAM theory, Nekhoroshev theory, normal form methods, exponential stability, Hamiltonian systems, celestial mechanics Citation: Giorgilli A., Locatelli U., Sansottera M.,  Secular Dynamics of a Planar Model of the Sun-Jupiter-Saturn-Uranus System; Effective Stability in the Light of Kolmogorov and Nekhoroshev Theories, Regular and Chaotic Dynamics, 2017, vol. 22, no. 1, pp. 54-77 DOI:10.1134/S156035471701004X