Minimization properties of Hill's orbits and applications to some N-body problems Gianni Arioli, Filippo Gazzola, Susanna Terracini (2000) Annales de l'I.H.P. Analyse non linéaire
Morse index properties of colliding solutions to the N-body problem Vivina Barutello, Simone Secchi (2008) Annales de l'I.H.P. Analyse non linéaire