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 Λ, 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 m ≠ 0) propagating on the light cone. In the limit of an infinite tower of these higher spin bosons and fermions, unitarity requires Λ to vanish