1/N-expansion and determination of resonance parameters in quantum mechanics

Suggestions have been made to treat the number of colors Nc in QCD as a large parameter and to use a 1/Nc-expansion. A large number of degrees of freedom leads to the classical limit and simplifies the dynamics. This is true in the quantum mechanical problem as well; here in analogy to Nc the large parameter is M=l+D/2 (l is the angular momentum and D the number of space dimensions). The development of the 1/n-expansion of N is presented. In addition to the analogy with 1/Nc, this expansion has useful applications in atomic physics and allows to compute the energy and width of resonances explicitly, including the strong coupling region. (Z.S.) 2 figs., 12 refs