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Dark matter possibly explained by axions?

  1. Oct 18, 2014 #1
    Last edited: Oct 18, 2014
  2. jcsd
  3. Oct 18, 2014 #2

    Chalnoth

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    Axions have long been one of the candidate models for dark matter. They're interesting because their production is completely different from the WIMP model (which uses a thermodynamic process). In the model, axions have a very small mass, but were created much earlier in the universe leading to such tremendously high abundance that there are enough of them to explain dark matter observations.

    There have been a number of experimental groups looking for signs of axions for years, so far without success. But as a rule, expect any preliminary signal like the one described in that article to probably be wrong. Nearly all such signals turn out to be wrong.
     
  4. Oct 18, 2014 #3
    "According to theory, axions are able to 'feel' electromagnetic interactions despite not carrying an electromagnetic charge"

    Clearly, that's nonsense.
     
  5. Oct 18, 2014 #4

    Chalnoth

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    Nope. In the presence of a strong magnetic field, photons can turn into axions, and vice versa.

    They certainly don't interact in the way an electric charge interacts (otherwise we would have detected them long ago). But there are other mechanisms.
     
  6. Oct 18, 2014 #5
    Aaa..that's something else then. Hmm, what's the energy threshold for that recation?
     
  7. Oct 18, 2014 #6

    mfb

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    The ALPS experiment looks for photon<->axion conversions of visible (soon infrared) light. Most axion models work with very small masses (<< eV), so I would expect the threshold somewhere at the axion mass.
     
  8. Oct 18, 2014 #7
    Haha, I thought the axion should be a particle with a huge mass.:) Well, good luck to ALPS but I'm affraid their efforts are doomed to failure.
     
  9. Oct 19, 2014 #8

    Chronos

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    From what i've read, axions are not massive enough to fill the bill.
     
  10. Oct 19, 2014 #9
    Frankly, I don't care if it fills a bill or not. However, I'd like to see a lab experiment like this one give a positive report about existance of axions in a near future. The experiment is very clever and beautiful :cool:
     
  11. Oct 19, 2014 #10

    ZapperZ

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    The problem with this is that you are trying to verify the existence of something using something that hasn't been found. How far out can you go on a hypothetical branch before it breaks?

    The last time a bunch of people jumped onto something that hasn't been fully verified (neutrino faster than light, anyone?), they all ended up with eggs on their faces! Haven't we learned from that already?

    Zz.
     
  12. Oct 19, 2014 #11
    After that poor Antonio Ereditato became better known as Erreditato :)
     
  13. Oct 19, 2014 #12
    I think that it is unfortunate that people receive ridicule when they make an honest mistake.
    All observations are useful, and proving falsehoods is useful also, for ruling out possibilities.
    Once you rule out the impossible whatever remains must be true.
    Perhaps we should also be keeping a record of untruths as well as accepted scientific facts.
     
  14. Oct 19, 2014 #13

    ZapperZ

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    There's a difference between an honest mistake, versus jumping in prematurely. I never ridiculed the OPERA result. They were honest in what they published, because that was what they found. And I will say the same thing with the BICEP2 results. Anyone who has followed my posts for any considerable period of time would have noticed that I often stated that we sometime learn a lot more from what doesn't work than from what does.

    So no, the "ridicule" here, if there is any ridicule at all, is not the SOURCE, but rather those who prematurely jumped onto the bandwagon without bothering to wait for the source to be verified! Those are the people that I questioned. I question their level of acceptance of what is valid and what isn't. And I question their motives in jumping in prematurely, in the hope of being the "first" to offer an explanation for what appeared to be something unexpected, all without waiting for it to be confirmed. This is not science, but rather the quest for fame and publicity!

    Zz.
     
  15. Oct 19, 2014 #14
    Zapper, my apologies, I didn't mean anyone here, I only meant in the most general terms. :)
    Perhaps there is a way for peer review instead of making a public announcement?
     
  16. Oct 19, 2014 #15

    ZapperZ

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    Peer review is never a guarantee that something is valid. Both OPERA and BICEP2 results were published in peer-reviewed journals.

    One should view any scientific endeavor as a PROCESS. In most cases, this is a very long, laborious process of verification and confirmation. In fact, I would say that it is never ending.

    The problem I have with what you posted is that one is building a speculation on top of another speculation. Axion has NOT been discovered. It's exact properties and behavior are unknown and only speculated. Dark Matter still hasn't been found, and even the exact properties of it are still highly debatable. So one is using something that is highly hypothetical to explain something that is still be debated and unclear. How much more speculative can you get? That is my whole issue! It is not an issue with dark matter, and it is not an issue with the search for axions. It is the issue of "I use this speculation to explain that speculation", and some people don't seem to have a problem with it!

    That is why I asked how far on the hypothetical branch are you willing to crawl on before you think it will break!

    Zz.
     
  17. Oct 19, 2014 #16

    mfb

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    All particle physics experiments have detailed internal review processes - even for normal publications with expected results. The chance that a few external experts see something tens to hundreds of experts in the collaboration familiar with the experiment miss is very small.
     
  18. Oct 19, 2014 #17
    I think this qualifies as "jumping in prematurely".:D We know that the OPERA result is invalid. We don't know that the BICEP2 result is invalid.

    In fact, there is a recent result that makes the PLANCK result more likely invalid. A group took the Planck extrapolation data which is now released, compared it with the released BICEP2 data, and concluded that Planck likely saw noise rather than dust - wrong signature, little match to the actual data - something that Planck has had problems with before IIRC. (E.g. their initial delay due to spurious noise in some data channels.)

    "The two maps show a positive correlation coefficient of 15.2% +/- 3.9% (1-sigma). This requires the amplitude of the Planck (50 < l <120) dust modes to be low in the BICEP2 region, and the majority of the Planck 353 GHz signal in the BICEP2 region in these modes to be noise. We can explain the observed correlation coefficient of 15.2% with a BICEP2 gravity wave signal with an rms amplitude equal to 54% of the total BICEP2 rms amplitude. The gravity wave signal corresponds to a tensor-to-scalar ratio r = 0.11 +/- 0.04 (1-sigma). This is consistent with a gravity wave signal having been detected, at a 2.5-sigma level."

    But it's an arxiv paper so far. And the mutual data comparison between the groups isn't done yet, so maybe Planck did see what they claimed they saw.

    [ http://arxiv.org/abs/1409.4491 ]

    Re axions, if the BICEP2 observations isn't all dust, I think an axion related mechanism of some sort is also the prime model for predicting the inflation field at such strengths. The usual scalar fields won't do I gather, problems with trans-Planckian values, but that axion mechanism will.

    Usually people who get signals that correlates with the seasons would go "bad experiment, large systematic effects", so I would add systematic effect elimination to the usual difficulties to get away from spurious statistics and "look elsewhere" effects with data-fishing for signals.
     
  19. Oct 19, 2014 #18

    mfb

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    resonaances, discussing this paper. The paper concludes that the BICEP2 data is consistent with r=0.

    We should see more measurements within a year.
     
  20. Oct 20, 2014 #19

    Chronos

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    I am curious, if you subject both data sets to Bayesian analysis, which is more probable?
     
  21. Oct 20, 2014 #20
    We are all curious. That is sort of what the PLANCK/BICEP groups should do next, merge them under that type of analysis. I think that would include grading quality of data.

    And hopefully more groups, or more of BICEPs Keck data (Keck is the next generation of their instruments), will contribute soon too.
     
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