A Classification of Dark Matter Candidates with Primarily Spin-Dependent Interactions with Matter

TL;DR

This paper classifies dark matter candidates with primarily spin-dependent interactions, showing that natural candidates are Majorana fermions or real vector bosons, and discusses their implications for collider and detection experiments.

Contribution

It provides a model-independent classification of spin-dependent WIMP dark matter candidates, identifying the natural types and their associated new particles near the weak scale.

Findings

Majorana fermions and real vector bosons are the natural dark matter candidates.

Scalar, Dirac fermion, and complex vector boson dark matter are generally disfavored.

New particles associated with these candidates are accessible at the LHC.

Abstract

We perform a model-independent classification of Weakly Interacting Massive Particle (WIMP) dark matter candidates that have the property that their scattering off nucleons is dominated by spin-dependent interactions. We study renormalizable theories where the scattering of dark matter is elastic and arises at tree-level. We show that if the WIMP-nucleon cross section is dominated by spin-dependent interactions the natural dark matter candidates are either Majorana fermions or real vector bosons, so that the dark matter particle is its own anti-particle. In such a scenario, scalar dark matter is disfavored. Dirac fermion and complex vector boson dark matter are also disfavored, except for very specific choices of quantum numbers. We further establish that any such theory must contain either new particles close to the weak scale with Standard Model quantum numbers, or alternatively, a $Z'$ gauge boson with mass at or below the TeV scale. In the region of parameter space that is of interest to current direct detection experiments, these particles naturally lie in a mass range that is kinematically accessible to the Large Hadron Collider (LHC).