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

TL;DR

The paper develops a model-independent classification of WIMP dark matter candidates whose nucleon scattering is dominated by spin-dependent interactions. By performing an operator analysis and examining renormalizable, elastic, tree-level theories, it shows that Majorana fermions and real vector bosons naturally yield predominantly SD scattering, while scalars and many Dirac/complex vector cases do not. It further demonstrates that theories with SD-dominant interactions require either new weak-scale mediators or a TeV-scale Z', making such models testable at the LHC, with direct-detection SD signals tightly correlated with collider phenomenology and neutrino-telescope constraints. The work highlights the interplay between direct detection, collider searches, and flavor constraints, providing a framework to interpret future SD signals in terms of underlying mediator spectra and symmetries.

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).

Figures (11)

• Figure 1: Scalar dark matter scattering diagrams
• Figure 2: Dirac fermion dark matter scattering diagrams
• Figure 3: Majorana fermion dark matter scattering diagrams
• Figure 4: Vector dark matter scattering diagrams
• Figure 5: Dirac dark matter scattering through t-channel vector exchange