Evidence Of Warm Dark Matter Annihilation Undermined

A new study fails to replicate the findings of five out of six papers that claim to have seen a 3.5 keV radiation line which arguably is the footprint of dark matter annihilation, using the same underlying data. 

The new study, with multiple authors, argues that the backgrounds were not correctly modeled and also identifies other methodological flaws in those papers. This greatly weakens on line of evidence in support of particle dark matter that can annihilate into ordinary matter or photons through collisions with other dark matter particles, which if the data were more solid would support a popular version of a warm dark matter particle model.

At least at face value, this is a rather stunning refutation of the work of the authors of the previous papers.

The 3.5 keV line is a purported emission line observed in galaxies, galaxy clusters, and the Milky Way whose origin is inconsistent with known atomic transitions and has previously been suggested to arise from dark matter decay. We systematically re-examine the bulk of the evidence for the 3.5 keV line, attempting to reproduce six previous analyses that found evidence for the line. Surprisingly, we only reproduce one of the analyses; in the other five we find no significant evidence for a 3.5 keV line when following the described analysis procedures on the original data sets. For example, previous results claimed 4σ

evidence for a 3.5 keV line from the Perseus cluster; we dispute this claim, finding no evidence for a 3.5 keV line. We find evidence for background mismodeling in multiple analyses. We show that analyzing these data in narrower energy windows diminishes the effects of mismodeling but returns no evidence for a 3.5 keV line. We conclude that there is little robust evidence for the existence of the 3.5 keV line. Some of the discrepancy of our results from those of the original works may be due to the earlier reliance on local optimizers, which we demonstrate can lead to incorrect results. For ease of reproducibility, all code and data are publicly available.  

Christopher Dessert, Joshua W. Foster, Yujin Park, Benjamin R. Safdi, "Was There a 3.5 keV Line?" arXiv:2309.03254 (September 6, 2023).