Infinitely Many Periodic Solutions for Some N-Body Type Problems with   Fixed Energies
  In this paper, we apply the Ljusternik-Schnirelman theory with local Palais-Smale condition to study a class of N-body problems with strong force potentials and fixed energies. Under suitable conditions on the potential $V$, we prove the existence of infinitely many non-constant and non-collision symmetrical periodic solutions . 
Pengfei Yuan and Shiqing Zhang
math-ph math.AP math.MP