M. Ramos et S. Terracini, NONCOLLISION PERIODIC-SOLUTIONS TO SOME SINGULAR DYNAMICAL-SYSTEMS WITH VERY WEAK FORCES, Journal of differential equations, 118(1), 1995, pp. 121-152
We prove a double variational characterization of the set of all the p
eriodic solutions of the Kepler problem. We provide a sufficient condi
tion for the existence of a periodic solution with prescribed period o
r energy for autonomous second-order differential systems with Kepleri
an-type potentials. The proofs are based on linking arguments. (C) 199
5 academic Press, Inc.