Gamma-ray lines may reveal the CP nature of the dark matter particle

TL;DR

This paper proposes that gamma-ray line observations from dark matter decay can reveal whether the dark matter particle is CP-even, CP-odd, or violates CP, based on correlations among decay channels.

Contribution

It introduces a method to determine the CP nature of spin-zero dark matter using gamma-ray line data and effective operator analysis under gauge invariance.

Findings

Correlations among gamma-ray decay channels depend on CP properties.

Future gamma-ray observations could identify the CP nature of dark matter.

Effective operators link decay modes to CP characteristics.

Abstract

Determining the fundamental properties of the dark matter is one of the most important open problems in particle physics today. If the dark matter particle has spin zero, one of these properties is its CP nature. That is, whether it is CP-even (scalar), CP-odd (pseudoscalar), or if its interactions violate CP. In this paper, we show that the observation of $\gamma$-ray lines arising from the decay of a spin-zero dark matter particle could be used to discriminate among these possibilities. We consider a general setup where dark matter decay is induced by effective operators and demonstrate that, due to gauge invariance, there exists correlations among the branching ratios into gauge boson final states ($\gamma\gamma$, $\gamma Z$, $W^+W^-$, $ZZ$) that depend on the mass and the CP properties of the dark matter. Consequently, the future observation of $\gamma$-ray lines may in principle be used to establish the CP nature of the dark matter particle.