Dark matter self-interactions from spin-2 mediators

We propose a new mechanism for making dark matter self-interacting in the presence of a massive spin-2 mediator. The derived Yukawa-type potential for dark matter is independent of the spins of dark matter, so are the resulting Sommerfeld effects for the dark matter self-scattering. We find that both the Born cross section and relatively mild Sommerfeld effects assist to make the self-scattering cross section velocity-dependent. We discuss how to evade the current indirect bounds on dark matter annihilations and show that the model is marginally compatible with perturbative unitarity in the ghost-free realization of the massive spin-2 particle.