A 3.55 keV hint for decaying axion-like particle dark matter

Understand

Recently, indications for an emission line at 3.55 keV have been found in the combined spectra of a large number of galaxy clusters and also in Andromeda.

• This line could not be identified with any known spectral line.
• It is tempting to speculate that it has its origin in the decay of a particle contributing all or part of the dark matter.
• In this note we want to point out that axion-like particles being all or part of the dark matter are an ideal candidate to produce such a feature.