On dark matter models with uniquely spin-dependent detection possibilities

TL;DR

This paper investigates dark matter models that are detectable through spin-dependent interactions but evade detection via spin-independent methods, highlighting the unique role of light pseudoscalar mediators.

Contribution

It identifies conditions under which dark matter models can be detected via spin-dependent interactions without accompanying spin-independent signals, focusing on models with light pseudoscalar mediators.

Findings

Most models with detectable spin-dependent interactions also produce detectable spin-independent signals.

Models with a light pseudoscalar mediator can evade spin-independent detection.

A specific viable dark matter model with such properties is presented.

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.