Stability of massive cosmological gravitons

We analyze the physics of massive spin-2 fields in (A)dS backgrounds and ex hibit that: The theory is stable only for masses m(2) greater than or equal to 2 Lambda /3, where the conserved energy associated with the background timelike Killing vector is positive, while the instability for m(2) < 2 Lam bda /3 is traceable to the helicity 0 energy. The stable, unitary, partiall y massless theory at m(2) = 2 Lambda /3 describes 4 propagating degrees of freedom, corresponding to helicities (+/-2, +/-1) but contains no 0 helicit y excitation. (C) 2001 Published by Elsevier Science B.V.