The $1:\pm2$ Resonance

    2007, Volume 12, Number 6, pp.  642-663

    Author(s): Cushman R., Dullin H. R., Hanßmann H., Schmidt S.

    On the linear level elliptic equilibria of Hamiltonian systems are mere superpositions of harmonic oscillators. Non-linear terms can produce instability, if the ratio of frequencies is rational and the Hamiltonian is indefinite. In this paper we study the frequency ratio $\pm 1/2$ and its unfolding. In particular we show that for the indefinite case ($1:-2$) the frequency ratio map in a neighborhood of the origin has a critical point, i.e. the twist condition is violated for one torus on every energy surface near the energy of the equilibrium. In contrast, we show that the frequency map itself is non-degenerate (i.e. the Kolmogorov non-degeneracy condition holds) for every torus in a neighborhood of the equilibrium point. As a by product of our analysis of the frequency map we obtain another proof of fractional monodromy in the $1:-2$ resonance.
    Keywords: resonant oscillators, normal form, singular reduction, bifurcation, energy-momentum mapping, monodromy
    Citation: Cushman R., Dullin H. R., Hanßmann H., Schmidt S., The $1:\pm2$ Resonance, Regular and Chaotic Dynamics, 2007, Volume 12, Number 6, pp. 642-663

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