I came across an article in The Guardian (definitely not the best source for science, but that's why I'm asking this question) that said that a team of scientists may have detected dark matter particles (characterized as axions) coming from the Sun. This seemed a little questionable, given how hard dark matter is to detect (and given how long scientists have searched for it). I have a multiple-part question:

  1. Have there been any independent peer-reviewed evaluations of the study? What were the conclusions regarding the accuracy of the results?
  2. How does the team know the supposed particles are axions, and not, say WIMPs?

The paper, by the way, can be found here.

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    $\begingroup$ One of the cool things about the arXiv is that they actually track citations of preprints/papers they host; in this case, none were found. $\endgroup$
    – Kyle Kanos
    Oct 19 '14 at 0:08
  • $\begingroup$ @KyleKanos That is cool. So that's an indication there were not other analyses? $\endgroup$
    – HDE 226868
    Oct 19 '14 at 0:10
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    $\begingroup$ I think it is safe to assume that the lack of citations indicate a lack of second analysis. Also, the M in WIMP is for massive (masses in the 100 GeV range), which might not interact to form Xrays in the <2 keV range--though I could be wrong on the inference there. $\endgroup$
    – Kyle Kanos
    Oct 19 '14 at 0:21
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    $\begingroup$ I think the paper is reasonably solid in its structure and approach, but it will take a lot more evidence (from this an independent experiments) to declare a detection. with regards to 2): That these are axions would follow from their radiation pattern in Earth's magnetic field. On a sad note, the first author of the paper, Prof. George Fraser from the University of Leicester has died in August. The news release by the university with tributes from his colleagues is here: www2.le.ac.uk/staff/community/people/bereavements/2014-archive/…. $\endgroup$
    – CuriousOne
    Oct 19 '14 at 5:09
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    $\begingroup$ @HDE226868: Here is an article in RAS: ras.org.uk/news-and-press/…. Interestingly, Fraser said "It appears plausible that axions – dark matter particle candidates – are indeed produced in the core of the Sun and do indeed convert to X-rays in the magnetic field of the Earth". However, axions are claimed to have no charge, aren't they? So magnetic field is participating in a transformation of a particle without charge into X-rays? $\endgroup$ Oct 20 '14 at 11:57

The paper has been severely criticised by Roncadelli & Tavecchio (2015). They note several important problems with Fraser et al.'s paper that they say make the conclusion that a signature of axions has been seen very unlikely.

Firstly, they do not dispute that Fraser et al. have seen an annually modulated X-ray background signal. The problem seems to be that these X-rays could be produced by axions in the geomagnetic field. Because XMM-Newton (the satellite in question) does not point at the Sun, then the X-ray photons need to have been scattered into the solid angle subtended by the XMM-Newton detectors that are pointing away from the Sun. It seems that the calculations of Fraser et al did not take into account the very large reduction in detected X-ray photons that results.

More minor(?) problems are that the axion-electron coupling constant estimated by Fraser et al. lies an order of magnitude higher than an upper limit found by new laboratory work and that this high coupling constant is inconsistent with a low-mass axion that is capable of being treated as cold dark matter.


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