A model-independent analysis of leptophilic dark matter at future
  electron-positron colliders in the mono-photon and mono-Z channels
  We consider the possibility that dark matter (DM) only interacts with the
Standard Model leptons, but not quarks at tree-level, and analyze the future
lepton collider prospects of such leptophilic DM in the mono-photon and
mono-$Z$ (both leptonic and hadronic) channels. Adopting a model-independent
effective field theory framework, we consider all possible dimension-6
operators of scalar-pseudoscalar (S-P), vector-axialvector (V-A) and
tensor-axialtensor (T-AT) types for a fermionic DM and derive the collider
sensitivities on the effective cut-off scale $\Lambda$ as a function of the DM
mass. As a concrete example, we take the beam configurations of the
International Linear Collider with $\sqrt s=1$ TeV and 1000 fb$^{-1}$
integrated luminosity, including the effect of beam polarization, and show that
it can probe leptophilic DM at $3\sigma$ level up to $\Lambda$ values of 4.8
TeV, 6.5 TeV and 5.3 TeV for the S-P, V-A and T-AT type operators respectively.
This is largely complementary to the direct and indirect searches for
leptophilic DM, and can potentially provide the best-ever sensitivity in the
low-mass DM regime.
