Including the Z in an Effective Field Theory for dark matter at the LHC

Understand

An Effective Field Theory for dark matter at a TeV-scale hadron collider should include contact interactions of dark matter with the partons, the Higgs and the Z.

• This note estimates the impact of including dark matter-Z interactions on the complementarity of spin dependent direct detection and LHC monojet searches for dark matter.
• Their effect is small, because they are suppressed by electroweak couplings and the contact interaction self-consistency condition $C/\Lambda^2 < 4\pi/\hat{s}$.
• In this note, the contact interactions between the Z and dark matter are parametrised by derivative operators; this is convenient at colliders because such interactions do not match onto the quark-dark matter contact interactions.