New Properties of Matter in (A)dS and their Consequences
  I review briefly, primarily for relativists, a series of recent results, obtained with A. Waldron, on the novel behavior of massive higher (s>1) spin systems in constant curvature backgrounds. We find that the cosmological constant Lambda, together with the mass parameter, define a "phase plane" in which partially massless gauge invariant lines separate allowed regions from forbidden, non-unitary, ones. These lines represent short multiplet systems, with missing lower helicities, removed by novel local gauge invariances, and (despite having nonvanishing m) propagating on the light cone. In the limit of an infinite tower of these higher spin bosons and fermions, unitarity requires Lambda to vanish. 
S. Deser