# Circularly Polarized Gamma Rays in Effective Dark Matter Theory

## TL;DR

This paper investigates the generation of circularly polarized gamma rays from dark matter annihilation via loop processes, highlighting potential observability in future gamma-ray polarimetry experiments.

## Contribution

It introduces a novel mechanism for circular polarization asymmetry in gamma rays from dark matter, considering both scalar and fermionic cases within effective theory.

## Key findings

- Asymmetry can reach nearly 90% for Z-photon final states.
- Circular polarization depends on CP violation in dark matter couplings.
- Future gamma-ray polarimetry could detect these polarization signals.

## Abstract

We study the loop-induced circularly polarized gamma rays from dark matter annihilation using the effective dark matter theory approach. Both neutral scalar and fermionic dark matter annihilating into monochromatic diphoton and $Z$-photon final states are considered. To generate the circular polarization asymmetry, $P$ and $CP$ symmetries must be violated in the couplings between dark matter and Standard Model fermions inside the loop with non-vanishing Cutkosky cut. The asymmetry can be sizable especially for $Z$-photon final state for which asymmetry of nearly $90\%$ can be reached. We discuss the prospect for detecting the circular polarization asymmetry of the gamma-ray flux from dark matter annihilation in the Galactic Center in future gamma-ray polarimetry experiments.