Anomalous X-Ray Galactic signal from 7 keV spin-$3/2$ dark matter decay

TL;DR

This paper proposes a model with a 7.1 keV spin-3/2 fermion as a dark matter candidate to explain the 3.55 keV x-ray line, fitting astrophysical and cosmological constraints.

Contribution

It introduces a minimal extension of the Standard Model with a neutral spin-3/2 fermion to account for the x-ray signal and dark matter properties.

Findings

The 7.1 keV fermion decay explains the 3.55 keV x-ray line.

The model fits dark matter relic density and astrophysical constraints.

Decay lifetime is consistent with observed x-ray flux.

Abstract

In order to explain the recently reported peak at $3.55$ keV in the galactic x-ray spectrum, we propose a simple model. In this model, the Standard Model is extended by including a neutral spin-$3/2$ vector-like fermion that transforms like a singlet under SM gauge group. This $7.1$ keV spin-$3/2$ fermion is considered to comprise a portion of the observed dark matter. Its decay into a neutrino and a photon with decay life commensurate with the observed data, fits the relic dark matter density and obeys the astrophysical constraints from the supernova cooling.