Heavy concerns about the light axino explanation of the 3.5 keV X-ray line

TL;DR

This paper critically examines the hypothesis that a 7 keV axino could explain the 3.5 keV X-ray line, highlighting significant theoretical challenges and suggesting a different candidate for the observed signal.

Contribution

It provides a model-independent analysis showing why axinos are unlikely to explain the 3.5 keV line, proposing a light metastable neutralino as a more plausible candidate.

Findings

Axino as a dark matter candidate faces significant obstacles.

A light metastable neutralino could potentially explain the X-ray line.

The axino explanation is considered unlikely based on the analysis.

Abstract

An unidentified 3.5 keV line from X-ray observations of galaxy clusters has been reported recently. Although still under scrutiny, decaying dark matter could be responsible for this signal. We investigate whether an axino with a mass of 7 keV could explain the line, keeping the discussion as model independent as possible. We point out several obstacles, which were overlooked in the literature, and which make the axino an unlikely candidate. The only viable scenario predicts a light metastable neutralino, with a mass between 0.1 and 10 GeV and a lifetime between $10^{-3}$ and $10^4$ s.