Self-interacting spin-2 dark matter

Recent developments in bigravity allow one to construct consistent theories of interacting spin-2 particles that are free of ghosts. In this framework, we propose an elementary spin-2 dark matter candidate with a mass well below the TeV scale. We show that, in a certain regime where the interactions induced by the spin-2 fields do not lead to large departures from the predictions of general relativity, such a light dark matter particle typically self-interacts and undergoes self-annihilations via 3-to-2 processes. We discuss its production mechanisms and also identify the regions of the parameter space where self-interactions can alleviate the discrepancies at small scales between the predictions of the collisionless dark matter paradigm and cosmological N-body simulations.

Figure 1

The portal communicating the spin-2 DM particle $\delta M$ to the SM fields is proportional to $\alpha$, whereas its self-interaction vertices are inversely proportional to powers of $\alpha$.

Figure 2

3-to-2 annihilation process of spin-2 DM particles.

Figure 3

Left: parameter space for self-interacting spin-2 DM when ${\beta }_1={\beta }_3$. The color gradient corresponds to the required reheating temperature $T_{\mathrm{RH}}$ to produce the observed relic abundance. The left gray region, corresponding to $T_{\mathrm{RH}}\ge {10}^{16}\mathrm{GeV}$ is considered to be strongly disfavored. The nonperturbativity region is given by $\alpha {\mathrm{m}}_{\mathrm{Pl}}\ge m_{\mathrm{FP}}$. Right: white region shows the DM mass range of interest as a function of $r$ to address small-scale problems (i.e., ${\sigma }_{\mathrm{SI}}/m_{\mathrm{FP}}\ge 0.1{\mathrm{cm}}^2/\mathrm{g}$) while being allowed by perturbativity requirement (e.g., the $r=0$ vertical line corresponds to the purple line in left panel). All hatched regions have been excluded in both panels.