Polarized gamma rays from dark matter annihilations

TL;DR

This paper investigates the potential for detecting linearly polarized gamma rays from dark matter annihilations in the Galactic center, proposing a model where polarization signals could reveal dark matter properties.

Contribution

It introduces a two-component dark matter model with Majorana fermions and an anapole moment, predicting detectable gamma-ray polarization signals at sub-GeV energies.

Findings

Polarized gamma-ray signals could be detectable with current X-ray polarimeters.

Degree of polarization can reach 70% or higher near the mass threshold.

Polarization signals provide a new method to probe dark matter properties.

Abstract

In this paper, we explore the possibility of a linearly polarized gamma-ray signal from dark matter annihilations in the Galactic center. Considering neutral weakly interacting massive particles, a polarized gamma-ray signal can be realized by a two-component dark matter model of Majorana fermions with an anapole moment. We discuss the spin alignment of such dark matter fermions in the Galactic center and then estimate the intensity and the polarizability of the final-state electromagnetic radiation in the dark matter annihilations. For low-mass dark matter, the photon flux at sub-GeV energies may be polarized at a level detectable in current X-ray polarimeters. Depending on the mass ratio between the final-state fermion and DM, the degree of polarization at the mass threshold can reach $70\%$ or even higher, providing us with a new tool for probing the nature of dark matter in future gamma-ray polarization experiments.