Anapole Dark Matter

TL;DR

This paper explores a unique form of dark matter interacting via an anapole moment, analyzing its annihilation properties, relic abundance, and detection prospects within current experimental limits.

Contribution

It introduces the concept of anapole dark matter, detailing its annihilation behavior and compatibility with cosmological and experimental constraints.

Findings

Anapole dark matter annihilates via p-wave into fermions.

The required anapole moment aligns with observed relic abundance.

Current detection limits are close to the predicted cross-section for certain masses.

Abstract

We consider dark matter (DM) that interacts with ordinary matter exclusively through an electromagnetic anapole, which is the only allowed electromagnetic form factor for Majorana fermions. We show that unlike DM particles with an electric or magnetic dipole moment, anapole dark matter particles annihilate exclusively into fermions via purely p-wave interactions, while tree-level annihilations into photons are forbidden. We calculate the anapole moment needed to produce a thermal relic abundance in agreement with cosmological observations, and show that it is consistent with current XENON100 detection limits on the DM-nucleus cross-section for all masses, while lying just below the detection threshold for a mass ~ 30-40 GeV.