We study dark matter interacting via a massive spin-2 mediator and pay close attention to dark matter annihilations into the mediator. Due to the high energy behavior of longitudinal modes of spin-2 particles, the rates of this channel exhibits a tremendous growth at large center of mass energies $\sqrt{s}$. To have a consistent effective theory for the spin-2 particle, we work in a warped extra-dimensional model such that the mediator(s) are the Kaluza-Klein (KK) modes of the 5D graviton. We find that truncating the KK-tower leads to an early breakdown of perturbative unitarity. However, by considering the full tower we obtain a set of sum rules for the couplings between the different KK-fields that restore unitarity up to the scale of the 5D theory. After including the full KK-tower in the dark matter production process the previously mentioned growth cancels and a more modest rate is found in the high energy limit. Interestingly, this implies that it is not possible to approximate the results obtained in the full theory with a reduced set of effective interactions once $\sqrt{s}$ is greater than the first graviton mass. This casts some doubt on the universal applicability of previous studies with spin-2 mediators within an EFT framework and prompts us to revisit the phenomenological allowed parameter space of gravitationally interacting scalar dark matter in warped extra-dimensions.
Sajad Abbar