Two-variable expansions of relativistic amplitudes and the subgroups of the SU(2,1) group

Abstract

A complete classification of the continuous subgroups of the SU(2,1) group is made in order to consider the possibility of writing two-variable expansions of relativistic amplitudes, incorporating the little group formalism and being explicitly crossing symmetric. It is shown that SU(2,1) has no E 2 subgroup and this severely limits the applicability of such expansions for the scattering of particles with non-equal masses.