On doubly symmetric periodic orbits

Abstract

AbstractIn this article, for Hamiltonian systems with two degrees of freedom, we studydoubly symmetricperiodic orbits, i.e., those which are symmetric with respect to two (distinct) commuting antisymplectic involutions. These are ubiquitous in several problems of interest in mechanics. We show that, in dimension four, doubly symmetric periodic orbits cannot be negative hyperbolic. This has a number of consequences: (1) All covers of doubly symmetric orbits aregood, in the sense of Symplectic Field Theory (Eliashberg et al. Geom Funct Anal Special Volume Part II:560–673, 2000); (2) a non-degenerate doubly symmetric orbit is stable if and only if its CZ-index is odd; (3) a doubly symmetric orbit doesnotundergo period doubling bifurcation; and (4) there is always a stable orbit in any collection of doubly symmetric periodic orbits with negativeSFT-Euler characteristic(as coined in Frauenfelder et al. in Symplectic methods in the numerical search of orbits in real-life planetary systems. PreprintarXiv:2206.00627). The above results follow from: (5) A symmetric orbit is negative hyperbolic if and only its twoB-signs(introduced in Frauenfelder and Moreno 2021) differ.