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Why not sterile particles as dark matter?

  1. Feb 21, 2016 #1

    bcrowell

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    It seems that the most popular hypothesis is that dark matter consists of WIMPs. Can the existing data be described with sterile particles rather than ones that interact through the weak force? Is the only reason to prefer WIMPs that they are predicted by SUSY? (To me, as a nonspecialist, SUSY seems like a failed idea.)
     
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  3. Feb 21, 2016 #2

    Vanadium 50

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    If the particles are truly sterile, how were they produced?
     
  4. Feb 21, 2016 #3

    bcrowell

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    Ah...that makes sense...

    I guess one possibility is they could have been created by gravitational processes in the very early universe, but then I suppose that in order to match the current density of dark matter, we would have needed a high density at early times, which would not be consistent with cosmological data. Or we could imagine sufficiently energetic gravitational processes in the more recent past, but that seems unlikely.

    Why do the above considerations not apply to sterile neutrinos, though? We can have neutrino oscillations to produce them, I guess...? I don't understand how this can be consistent with the observed solar neutrino flux.

    Is it possible to make their electroweak charge very small (much less than for neutrinos or quarks), but not zero? I would think that their rate of production would then be very small, but their rate of annihilation would also be very small. Wouldn't that imply that their equilibrium concentration could be significant? Or is there some principle similar to quantization of electric charge that says you can't have an electroweak charge less than the standard unit?
     
  5. Feb 21, 2016 #4

    Vanadium 50

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    There are only two problems with sterile neutrinos: "sterile" and "neutrinos".

    Absolutely sterile we covered. You're right that almost sterile might be made to work, depending on how almost is almost. Neutrinos have the additional problem that they move too fast to create the large scale structure we see. If you try and make the sterile neutrino heavy to fix that, its oscillation probability goes way, way down, so you don't make very many. (ueV things mix poorly with GeV things)
     
  6. Feb 21, 2016 #5
    would axions or ultra light scalar qualify as sterile?
     
  7. Feb 22, 2016 #6

    Haelfix

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    Yea typically sterile neutrinos that are used for the purpose of creating dark matter have a significant production problem. Most of the methods (resonant production etc) found in the literature don't really work well from a model building point of view (they typically lead to conflicts with structure formation), but the method that is still viable is relatively low kev mass neutrinos produced via the decay of a heavy scalar. Often this is wrapped into the physics of the inflaton, but in principle it could come from many different larger embeddings.
     
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