Direct Detection with Dark Mediators

We introduce dark mediator Dark matter (dmDM) where the dark and visible sectors are connected by at least one light mediator $ϕ$ carrying the same dark charge that stabilizes DM. $ϕ$ is coupled to the Standard Model via an operator $\bar q q ϕϕ^*/Λ$, and to dark matter via a Yukawa coupling $y_χ\overline{χ^c}χϕ$. Direct detection is realized as the $2\rightarrow3$ process $χN \rightarrow \bar χN ϕ$ at tree-level for $m_ϕ\lesssim 10 \ \mathrm{keV}$ and small Yukawa coupling, or alternatively as a loop-induced $2\rightarrow2$ process $χN \rightarrow χN$. We explore the direct-detection consequences of this scenario and find that a heavy $\mathcal{O}(100 \ \mathrm{GeV})$ dmDM candidate fakes different $\mathcal{O}(10 \ \mathrm{GeV})$ standard WIMPs in different experiments. Large portions of the dmDM parameter space are detectable above the irreducible neutrino background and not yet excluded by any bounds. Interestingly, for the $m_ϕ$ range leading to novel direct detection phenomenology, dmDM is also a form of Self-Interacting Dark Matter (SIDM), which resolves inconsistencies between dwarf galaxy observations and numerical simulations.

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