Group-theoretical analysis of elementary particles in an external electromagnetic field - I. The relativistic particle in a constant and uniform field

Abstract

Two subgroups of the Poincaré group are shown to play a particlar role in the case of charged systems in an external electromagnetic field which is constant and uniform. Projective representations of these subgroups involve the electric charge as a generator of a phase factor. Additivity and superselection rules for charge appear as direct consequences. © 1970 Società Italiana di Fisica.