Despicable Dark Relics: generated by gravity with unconstrained masses

Abstract

We demonstrate the existence of a generic, efficient and purely gravitational channel producing a significant abundance of dark relics during reheating after the end of inflation. The mechanism is present for any inert scalar with the non-minimal curvature coupling $\xi R{\chi }^2$ and the relic production is efficient for natural values $\xi =\mathcal{O}(1)$. The observed dark matter abundance can be reached for a broad range of relic masses extending from $m\sim 1\mathrm{keV}$ to $m\sim 10^8\mathrm{GeV}$, depending on the scale of inflation and the dark sector couplings. Frustratingly, such relics escape direct, indirect and collider searches since no non-gravitational couplings to visible matter are needed.

Comments: 24 pages, 8 figures, published in JCAP