DAMA/LIBRA and leptonically interacting Dark Matter
  We consider the hypothesis that Dark Matter (DM) has tree-level interactions
only with leptons. Such a framework, where DM recoils against electrons bound
in atoms, has been proposed as an explanation for the annually modulated
scintillation signal in DAMA/LIBRA versus the absence of a signal for nuclear
recoils in experiments like CDMS or XENON10. However, even in such a
leptophilic DM scenario there are loop induced DM-hadron interactions, where
the photons emitted from virtual leptons couple to the charge of a nucleus.
Using a general effective field theory approach we show that, if such an
interaction is induced at one or two-loop level, then DM-nucleus scattering
dominates over DM-electron scattering. This is because the latter is suppressed
by the bound state wave function. One obtains a situation similar to standard
DM-nucleus scattering analyses with considerable tension between the results of
DAMA and CDMS/XENON10. This conclusion does not apply in the case of
pseudoscalar or axial vector coupling between DM and leptons, where the loop
diagrams vanish. In this case the explanation of the DAMA signal in terms of
DM-electron scattering is strongly disfavored by the spectral shape of the
signal. Furthermore, if DM can annihilate into neutrinos or tau leptons, the
required cross sections are excluded by many orders of magnitude using the
Super-Kamiokande bound on neutrinos from DM annihilations in the Sun.
