  The strong direct detection limits could be pointing to dark matter --
nucleus scattering at loop level. We study in detail the prototype example of
an electroweak singlet (Dirac or Majorana) dark matter fermion coupled to an
extended dark sector, which is composed of a new fermion and a new scalar.
Given the strong limits on colored particles from direct and indirect searches
we assume that the fields of the new dark sector are color singlets. We outline
the possible simplified models, including the well-motivated cases in which the
extra scalar or fermion is a Standard Model particle, as well as the possible
connection to neutrino masses. We compute the contributions to direct detection
from the photon, the $Z$ and the Higgs penguins for arbitrary quantum numbers
of the dark sector. Furthermore, we derive compact expressions in certain
limits, i.e., when all new particles are heavier than the dark matter mass and
when the fermion running in the loop is light, like a Standard Model lepton. We
study in detail the predicted direct detection rate and how current and future
direct detection limits constrain the model parameters. In case dark matter
couples directly to Standard Model leptons we find an interesting interplay
between lepton flavor violation, direct detection and the observed relic
abundance.

High Energy Physics - Phenomenology