New Properties of Matter in (A)dS and their Consequences

TL;DR

This paper explores the behavior of massive higher spin systems in (A)dS spaces, revealing a phase structure governed by the cosmological constant and mass, with implications for unitarity in theories with infinite higher spin towers.

Contribution

It introduces the concept of a phase plane for higher spin fields in (A)dS, identifying gauge-invariant lines that separate allowed and forbidden regions, and discusses unitarity constraints for infinite higher spin spectra.

Findings

Partially massless lines define boundaries in the phase plane.

Short multiplet systems with missing helicities are identified.

Unitarity requires the cosmological constant to vanish in infinite higher spin towers.

Abstract

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.