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_νλ…^′≡γ^μh_μνλ… does not vanish, and neither does h^′′≡(h^′)^′; but h^′′′ does vanish. The wave equation admits a gauge group, h→h+sym grad  ξ, with ξ^′=0. The most interesting feature is that the source t need not be divergence free, only the traceless part of p^μt_μν… must vanish. This weaker condition on t turns out to be sufficient to guarantee that only helicities±s are transmitted between sources.