Extra light fermions in $E_6$-inspired models and the 3.5 keV X-ray line signal

TL;DR

This paper proposes that light fermions from an $E_6$-inspired model can serve as dark matter, explaining the 3.5 keV X-ray line through their radiative decay into neutrinos and photons.

Contribution

It introduces a novel dark matter candidate within an $E_6$-inspired U(1) extension that accounts for the 3.5 keV X-ray line via radiative decay.

Findings

Light fermions (~7 keV) decay produce the X-ray line.

Decay lifetime matches observational constraints.

Model integrates dark matter and dark radiation aspects.

Abstract

We propose a scenario in which extra light fermions in an $E_6$-inspired U(1) extension of the standard model constitute the dark matter, as a simple variation of our model for dark radiation presented in 2010. Interestingly, for the light fermions of mass about 7 keV, they radiatively decay into active neutrinos and photons with a lifetime in the range of $10^{27}-10^{28}$ seconds, which naturally explains the recently discovered 3.5 keV X-ray line signal.