On dark matter models with uniquely spin-dependent detection possibilities

Abstract

With much higher sensitivities due to coherence effects, it is often assumed that the first evidence for direct dark matter detection will come from experiments probing spin-independent interactions. We explore models that would be invisible in such experiments, but detectable via spin-dependent interactions. The existence of much larger (or even only) spin-dependent tree-level interactions is not sufficient, due to potential spin-independent subdominant or loop-induced interactions. We find that in such a way most models with detectable spin-dependent interactions would also generate detectable spin-independent interactions. Models in which a light pseudoscalar acts as the mediator seem to uniquely evade this conclusion. We present a particular viable dark matter model generating such an interaction.

Comments: 11 pages, 3 figures, v2: added closed form expressions for pseudoscalar loops and discussion of collider bounds. References added, v3: to match version appearing in PRD, numerical error in eq. 2 corrected