The $(m^2,\Lambda )$ plane of spin $s>\mathrm{}1\mathrm{}$ massive fields in (anti-) de Sitter space backgrounds is shown to consist of separate phases, divided by lines of novel “partially massless” gauge theories that successively remove helicities, starting from the lowest, 0 or $\pm 1/2$. The norms of the excluded states flip as the gauge lines are crossed and only the region containing the massive Minkowski theory is unitary. The partially massless gauge theories are unitary or not, depending on the ordering of the gauge lines. This “level splitting” of massless Minkowski gauge theories is specific to nonzero $\Lambda$.

We study topologically massive (2+1)-dimensional gravity with a negative cosmological constant. The masses of the linearized curvature excitations about AdS_3 backgrounds are not only shifted from their flat background values but, more surprisingly, split according to chirality. For all finite values of the topological mass, we find a single bulk degree of freedom with positive energy, and exhibit a complete set of normalizable, finite-energy wave packet solutions. This model can also be written as a sum of two higher-derivative SL(2,R) Chern--Simons theories, weighted by the central charges of the boundary conformal field theory. At two particular "critical" values of the couplings, one of these central charges vanishes, and linearized topologically massive gravity becomes equivalent to topologically massive electromagnetism; however, the physics of the bulk wave packets remains unaltered here.