Composite magnetic dark matter and the 130 GeV line

TL;DR

This paper proposes a composite dark matter model with a magnetic dipole moment to explain the 130 GeV gamma-ray line, predicting specific collider signatures and addressing challenges in model realization.

Contribution

It introduces a novel composite dark matter model with a large magnetic dipole moment to account for the gamma-ray line, highlighting its naturalness and collider implications.

Findings

Dark matter with a magnetic dipole can explain the 130 GeV line.

Predicted collider signature includes 4-photon events from bound state decays.

Model faces challenges in achieving the required dipole moment.

Abstract

We propose an economical model to explain the apparent 130 GeV gamma ray peak, found in the Fermi/LAT data, in terms of dark matter annihilation through a dipole moment interaction. The annihilating dark matter particles represent a subdominant component, with mass density 7-17% of the total DM density; and they only annihilate into gamma gamma, gamma Z, and ZZ, through a magnetic (or electric) dipole moment. Annihilation into other standard model particles is suppressed, due to a mass splitting in the magnetic dipole case, or to p-wave scattering in the electric dipole case. In either case, the observed signal requires a dipole moment of strength mu ~ 2/TeV. We argue that composite models are the preferred means of generating such a large dipole moment, and that the magnetic case is more natural than the electric one. We present a simple model involving a scalar and fermionic techniquark of a confining SU(2) gauge symmetry. We point out some generic challenges for getting such a model to work. The new physics leading to a sufficiently large dipole moment is below the TeV scale, indicating that the magnetic moment is not a valid effective operator for LHC physics, and that production of the strongly interacting constituents, followed by techni-hadronization, is a more likely signature than monophoton events. In particular, 4-photon events from the decays of bound state pairs are predicted.