# The dark matter interpretation of the 3.5-keV line is inconsistent with blank-sky observations

## TL;DR

This study tests the dark matter decay hypothesis for the 3.5-keV X-ray line using extensive XMM-Newton observations of the Milky Way halo, finding no supporting evidence and challenging the dark matter interpretation.

## Contribution

It provides the first comprehensive analysis of the Milky Way halo data, setting upper limits that conflict with the dark matter decay explanation for the 3.5-keV line.

## Key findings

- No 3.5-keV line detected in the Milky Way halo
- Upper limits on dark matter decay rate established
- Dark matter decay hypothesis for the line is inconsistent with observations

## Abstract

Observations of nearby galaxies and galaxy clusters have reported an unexpected X-ray emission line around 3.5 kilo-electron volts (keV). Proposals to explain this line include decaying dark matter$-$in particular, that the decay of sterile neutrinos with a mass around 7 keV could match the available data. If this interpretation is correct, the 3.5 keV line should also be emitted by dark matter in the halo of the Milky Way. We used more than 30 megaseconds of XMM-Newton (X-ray Multi-Mirror Mission) blank-sky observations to test this hypothesis, finding no evidence of the 3.5-keV line emission from the Milky Way halo. We set an upper limit on the decay rate of dark matter in this mass range, which is inconsistent with the possibility that the 3.5-keV line originates from dark matter decay.