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 q-qϕϕ*/Λ, and to dark matter via a Yukawa coupling yχχc-χϕ. Direct detection is realized as the 2→3 process χN→χ-Nϕ at tree-level for mϕ≲10 keV and small Yukawa coupling, or alternatively as a loop-induced 2→2 process χN→χN. We explore the direct-detection consequences of this scenario and find that a heavy O(100 GeV) dmDM candidate fakes different O(10 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 mϕ 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.
Curtin, D., Surujon, Z., & Tsai, Y. (2014). Direct detection with dark mediators. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 738, 477–482. https://doi.org/10.1016/j.physletb.2014.10.027