The diffeomorphism invariance of a compactified five-dimensional theory of gravity is spontaneously broken by the background space-time geometry. In this talk I will discuss the surprising properties of the scattering amplitudes of the massive spin-2 Kaluza-Klein modes of these theories, and explain the origin of these properties in terms of underlying hidden symmetries. I will also discuss the phenomenology of dark-matter (DM) scenarios within radius-stabilized Randall-Sundrum models. Specifically, we consider models where the dark matter candidates are Standard Model (SM) singlets confined to the TeV brane and interact with the SM via spin-2 and spin-0 gravitational Kaluza-Klein (KK) modes. Considering the resulting DM abundance, collider searches, and the absence of a signal in direct DM detection experiments, we show that spin-2 KK portal DM models are highly constrained. In particular we show that within the usual thermal freeze-out scenario, scalar and fermion dark matter models are ruled out, while vector dark matter models are still viable for a certain region of parameter space.
