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If Sterile neutrino and axions exist, is that standard model

  1. Dec 2, 2015 #1
    it's commonly stated that the standard model has no dark matter candidate.

    axions and/or sterile neutrions are well motivated extensions of the standard model. if experiments show they exist and are a part of dark matter, would this still be within the framework of the standard model, or is it BSM?

    would the existence of a standard model that includes axions and/or sterile neutrions still be considered the standard model or something else?

    if dark matter consists of axions and/or sterile neutrions or both, then can it be said the standard model does explain dark matter?
  2. jcsd
  3. Dec 2, 2015 #2


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    No, neither axions nor sterile neutrinos are part of the standard model. Of course, if they were detected, a new standard model would likely develop that include them.
  4. Dec 2, 2015 #3
    but they can easily be accommodated in the current standard model is my point.
  5. Dec 2, 2015 #4
    No. SM has no possibilities to explain this.
    And if an Axion really exists, then it is not clear what kind of properties it should have in respect of mass. For euclidan space in QCD and even QFT it should have a minimal mass. But in Stringtheory it is mathematically and very hypothetically only a graviton with spin 0 without mass. Then we would have a true problem. I think it doesn't exist. It is only a mathematical curiosity like ghostfields
  6. Dec 2, 2015 #5
    They would both be considered BSM. Axions are a species of particle simply not present in the standard model.

    Neutrinos, on the other hand, are present- or at least "left handed" neutrinos are. The thing is that in the SM, from the viewpoint of the fundamental definition of the theory, "left and right handed versions" of a particle are basically different types of particle- for example, they have different hypercharges. We call both left and right handed electrons "electrons" because the interactions of both these particles with the Higgs swaps them between each other. Now, for the neutrino to gain a mass in this way is tricky, because it's considerably lighter than everything else, so there are arguments to suggest that the neutrino mass is associated with genuinely radically new physics at an energy scale much higher than any we have ever probed experimentally.

    I'd usually require a graviton to have spin 2. Are you thinking of something like a dilaton?
  7. Dec 2, 2015 #6
    Originally, the Standard Model said that neutrinos were massless, so when it was discovered that neutrinos had mass (which led to this year's Nobel Prize), it was originaly considered an extension of the Standard Model. People would speak of "the Standard Model plus neutrino masses". However, as years passed, it became so firmly established that neutrinos have mass, and it's a relatively small modification of the Standard Model, as opposed to grand unification or supersymmetry, that it became incorporated into the Standard Model. Today, when people say "the Standard Model", they are including within the phrase, the assumption that neutrinos have mass. I predict that people would follow a similar pattern regarding sterile neutrinos and axions. At first, they would be considered an extension of the Standard Model, but as time went on, they incorporated into the Standard Model.

    There is probably more than one particle that we collectively refer as "dark matter". Often people speak of the "dark sector". Sterile neutrinos and axions might contribute, but they could not alone, completely explain dark matter.
  8. Dec 2, 2015 #7


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    This is not really true. The phrase "Standard Model" still does not incorporate neutrino masses, mainly because it is not clear how neutrino masses arise or whether or not they are Dirac or Majorana masses. There are several possible mechanisms behind neutrino masses and there is therefore not a single one that can be considered "standard". However, when people are talking about the standard model, they usually do so with the knowledge that it needs to be modified in order to accommodate neutrino masses in one way or another. Luckily (or sadly, depending on the point of view) the low energy effects, i.e., the effects we can see in neutrino oscillation experiments, are essentially identical regardless of how the standard model is extended to include neutrino masses.
  9. Dec 2, 2015 #8
    Yes Dilaton and Axion are mathematically Gravitons with spin 0
    Graviton is the same only with spin 2

    But Ed Witten has written a pub about Axion in Stringtheory. I haven't read it so far.
    I will look for it.
    Axions In String Theory
    Peter Svrˇcek
    Department of Physics and SLAC, Stanford University, Stanford CA 94305/94309 USA
    and Edward Witten Institute For Advanced Study, Princeton NJ 08540 USA
    SLAC-PUB-11894 astro-ph/0605206 Mah 2006
  10. Dec 2, 2015 #9
    axions, in its original motivation,would be a pretty minimal and trivial modification of current SM
  11. Dec 3, 2015 #10
    I looked now in the paper of Ed Witten and Peter Svricek which describes all possibilities in any stringtheorey. An Axion is without mass there. In Stringtheory an Axion is not spontanously symmetry broken like it is predicted in QCD and does not get mass through Higgs mechanism like in QFT. That's the reason.
  12. Dec 3, 2015 #11
    Can I ask why you say they are "like a graviton with spin zero"? To me a graviton is necessarily a spin -2 particle
    -the spin, the gauge symmetry corresponding to classical diffeomorphism invariance, and the fact that it couples to the energy-momentum tensor are all closely interrelated.
  13. Dec 3, 2015 #12
    because my description is from the string theory. I prefer to think now first from the stringtheory perspective and later compare it with QFT.
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