Massless Particle with Spin j ~ 1 Implies the S-Matrix Symmetry

We analyse the properties of massless (bose or fermi) particles with spin j;;;; I that have non-vanishing couplings in the infrared limit. It is shown that the existence of such massless particles necessarily implies the " S-matrix gauge-invariance " relation. These lead, in partic-ular, to the existence of a physicalS-matrix symmetry corresponding to the tensor (tensor-spinor) source charge of that massless particle. For instance, for a spin 3/2 massless Rarita-Schwinger particle, there must exist a supersymmetry. As a preliminary for these arguments, we shall clarify the nature of Lorentz group representation of massless particle in covariant field theory with indefinite metric and contrast it with that in Wigner's (positive metric) representa-tion theory