It has been suggested that elementary particles should be associated with the irreductible representations of the Bondi-Metzner-Sachs group, on the grounds that in these, only discrete spins appear. We emphasize that the last statement strongly depends on the topology originally chosen for supertranslations, and we discuss in some detail how continuous spins appear when other equally reasonable topologies are chosen, which depend in a more explicit way on the smoothness of supertranslations.

• Received 28 August 1973

DOI:https://doi.org/10.1103/PhysRevLett.32.565