1/N expansion for three-body problem

The expansion in powers of 1/N (N is the dimension of the space) is used for calculating the energy of the bound states of a quantum-mechanical three-body system. The limit N → ∞ is proved to correspond to the classical motion of a rigid configuration of particles in the four-dimensional space. The results of summing the 1/N power series are discussed using as examples the anharmonical oscillator, the mesoatom μμα, and screened helium