
Figure 1: Spectral representation of different models. (a) DGP (b) higher-dimensional cascading
gravity and (c) multi-gravity. Bi-gravity is the special case of multi-gravity with one massless mode
and one massive mode. Massive gravity is the special case where only one massive mode couples to
the rest of the standard model and the other modes decouple. (a) and (b) are models of soft massive
gravity where the graviton mass can be thought of as a resonance.