Stability of massive cosmological gravitons

We analyze the physics of massive spin-2 fields in (A)dS backgrounds and exhibit that: The theory is stable only for masses m2⩾2Λ/3, where the conserved energy associated with the background timelike Killing vector is positive, while the instability for m2<2Λ/3 is traceable to the helicity 0 energy. The stable, unitary, partially massless theory at m2=2Λ/3 describes 4 propagating degrees of freedom, corresponding to helicities (±2,±1) but contains no 0 helicity excitation.