In this talk, we deal with a periodic perturbation of a central force problem. Based on the introduction of suitable time-maps (the radial period and the apsidal angle) for the unperturbed problem and of an associated non-degeneracy condition (not requiring the explicit knowledge of the Hamiltonian in action-angle coordinates), we apply a higher-dimensional version of the Poincaré-Birkhoff fixed point theorem to prove the existence of non-circular periodic solutions bifurcating from invariant tori. Next, we show that this non-degeneracy condition is satisfied for some concrete examples of physical interest. At last, an application is given to a restricted 3-body problem with a non-Newtonian interaction.
The talk is based on joint work with Alberto Boscaggin and Walter Dambrosio (University of Torino).