It has been proposed that the Bondi-Metzner-Sachs group affords a possible explanation for the discreteness of elementary-particle spins. This discreteness result depends on the topology given to the group. A careful analysis of representations in the "nuclear" topology indicates that discrete-spin representations (those subsumed by the original topology) describe bound gravitating systems ("elementary particles") whereas the new continuous-spin representations, if physically realistic, describe scattering states of gravitating systems.

• Received 22 April 1974

DOI:https://doi.org/10.1103/PhysRevLett.33.547