  We introduce dark mediator Dark matter (dmDM) where the dark and visible
sectors are connected by at least one light mediator $\phi$ carrying the same
dark charge that stabilizes DM. $\phi$ is coupled to the Standard Model via an
operator $\bar q q \phi \phi^*/\Lambda$, and to dark matter via a Yukawa
coupling $y_\chi \overline{\chi^c}\chi \phi$. Direct detection is realized as
the $2\rightarrow3$ process $\chi N \rightarrow \bar \chi N \phi$ at tree-level
for $m_\phi \lesssim 10 \ \mathrm{keV}$ and small Yukawa coupling, or
alternatively as a loop-induced $2\rightarrow2$ process $\chi N \rightarrow
\chi N$. 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
$m_\phi$ 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.

High Energy Physics - Phenomenology