The closedness of orbits of central forces is addressed in a three-dimensional space in which the Poisson bracket among the coordinates is that of the SU(2) Lie algebra. In particular it is shown that among problems with spherically symmetric potential energies, it is only the Kepler problem for which all bounded orbits are closed. In analogy with the case of the ordinary space, a conserved vector (apart from the angular momentum) is explicitly constructed, which is responsible for the orbits being closed. This is the analog of the Laplace–Runge–Lenz vector. The algebra of the constants of the motion is also worked out.
Partial wave expansions for arbitrary spin and the role of non-central forces. [Orbital angular momentum, diagonal and nondiagonal matrix elements]
