Massless fields with half-integral spin

The Fierz-Pauli Lagrangian for massive particles with spin s = n + 1/2, n integer, is examined in the limit of vanishing mass. A considerable simplification occurs. The potential h is a Rarita-Schwinger spinor-tensor of tensorial rank n. The ''spinor-trace'' h', defined by h/sup prime//sub nulambda.../ equivalent γ/sup μ/h/sub munulambda.../ does not vanish, and neither does h'' equivalent (h') '; but h''' does vanish. The wave equation admits a gauge group, h → h + sym grad xi, with xi' = 0. The most interesting feature is that the source t need not be divergence free, only the traceless part of p/sup μ/t/sub munu.../ must vanish. This weaker condition on t turns out to be sufficient to guarantee that only helicities +- s are transmitted between sources