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B Dark Matter

  1. Jun 14, 2018 #1
    I would like to hear what the opinions are.
    Could sterile neutrino's be dark matter?
    I'm sure this has been discussed if not here then somewhere.
     
  2. jcsd
  3. Jun 15, 2018 #2

    Orodruin

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    This depends on the properties of said sterile neutrino. Sterile neutrinos have certainly been discussed as a dark matter candidate, typically with masses around the keV scale. Did you have a particular mass range in mind?
     
  4. Jun 15, 2018 #3
    No not a mass. Was just reading that they may have been found by the Liquid Scintillator Neutrino Detector and it seemed that if they are so hard to detect here on earth then they may be a candidate for Dark Matter.
     
  5. Jun 15, 2018 #4

    Orodruin

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    So implicitly you are assuming a mass scale, that of the hypothetical sterile suggested as a reason for the LSND anomaly. No, that sterile cannot be dark matter. It has several issues with cosmology. Also note that the LSND experiment is rather old and its results have been known for a long time. Its interpretation in terms of a sterile neutrino is doubtful based on the global experimental status. You may have been alerted by the latest results of MiniBooNE, which are discussed here.
     
  6. Jul 15, 2018 #5
    dark matter must consist of some kind of unseen particles
    Dirac called these unseen particles '' negative virtual particles''
    and wrote them by the formula: -E=Mc^2
    ===
     
  7. Jul 15, 2018 #6

    Orodruin

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    No it must not.

    No he did not. You are confusing dark matter with the idea of a Dirac sea.
     
  8. Jul 15, 2018 #7
    Every matter consists of particles.
    What does dark matter consist of ?
    ===
     
  9. Jul 15, 2018 #8

    Orodruin

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    Not necessarily. You need to go quite far beyond B-level to understand what is meant by "matter" in the context of cosmology and astrophysics.

    We do not know. Particle dark matter is a popular theory, but it has not been experimentally verified.
     
  10. Jul 15, 2018 #9

    Chronos

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    There is still plenty of evidence remains favoring sterile neutrinos as dark matter. Unexplained xray emission lines from galactic clusters are probably the best evidence to date for sterile neutrino DM. Factors which also favor sterile neutrino dark matter include pulsar kicks and galactic density profiles which suggest central DM cusps over DM core cusps. Astronomical data currently suggests warm DM may be preferred over cold DM models The best evidence may yet come from the LHC, once it reaches the !4 TEV range as planned in 2025 - re: https://arxiv.org/abs/1703.01934, Signatures of Dirac and Majorana Sterile Neutrinos in Trilepton Events at the LHC.
     
    Last edited: Jul 15, 2018
  11. Jul 16, 2018 #10
    My understanding of any type a neutrino being dark matter is that since neutrinos travel at close to the speed of light they can only be considered as candidates for hot dark matter. It is, also, disappointing that theorists are always suggesting that the answer is just over another hill be it higher energies at LHC or a bigger vat of Xenon.
     
  12. Jul 16, 2018 #11

    Chronos

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    That argument argument originated when neutrinos were believed to be massless and simulations ruled out hot [relativistic] neutrinos as the principle form of DM. The argument has become more one of how much mass is necessary to rule out neutrinos as a viable DM candidate. The unidentified xray line in cluster spectrographs has pegs the prospective DM neutrino mass at around 7 Kev - more than enough to refute the hot DM objection. If the sterile neutrino is confirmed, it could be even more massive.
     
  13. Jul 16, 2018 #12
    I am still not convinced. I am aware that neutrinos have mass but this is very small and as I believe they still travel at close to the speed of light so they should still be considered as relativistic particles. You quoted an energy of 7 KeV but this is a composite of velocity and mass so are these proposed sterile neutrinos low mass and fast moving or high mass and slower which would make them singular neutrinos?
     
  14. Jul 16, 2018 #13

    Orodruin

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    You are thinking of standard model neutrinos, not sterile neutrinos. Sterile neutrinos with a large mass remains a possible dark matter candidate although mixing would have to be very suppressed. However, it should be mentioned that models including sterile neutrino DM are typically rather fine-tuned and the 7 keV line is by no means necessarily from DM annihilation.
     
  15. Jul 16, 2018 #14

    Chronos

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    Last edited: Jul 16, 2018
  16. Jul 17, 2018 #15
    Having done a little searching as well as checking the two abstracts of the references Chronos gave, it appears a bit of a fudge to even call these particles neutrinos which apparently only act via gravity and not the weak force, which seems to make them only yet another hypothetical dark matter particle, sharing only a name with the known neutrinos. Maybe giving them half a familiar name was an attempt to gain quicker acceptance rather then just another DM particle.
     
  17. Jul 17, 2018 #16

    Orodruin

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    I disagree, it is standard nomenclature to call a standard model singlet fermion "sterile neutrino". Also, please note that their introduction is not mainly as a dark matter candidate, but typically as a means of introducing neutrino mass - this is the reason to call them sterile or right-handed neutrinos. Once introduced, these fermions allow a Majorana mass term and its scale essentially determines the possible phenomenology.
     
  18. Jul 17, 2018 #17
    I might be getting this wrong but aren't right handed neutrinos, anti-neutrinos.
     
  19. Jul 17, 2018 #18

    Orodruin

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    Yes and no. It would be more accurate to say that standard model anti-neutrinos are right-handed. Typically, when we talk about right-handed neutrinos we do mean right-handed neutrinos, which is a hypothetical standard model singlet, not right-handed anti-neutrinos.
     
  20. Jul 17, 2018 #19
    Ok, I understand your point. We are living in exciting times in astronomy and I am in no way suggesting that the experiments being planned should not go ahead but I do think that many of the issues dark matter is trying to solve have been solved better without it, and I do not mean by modified theories of gravity.
     
  21. Jul 17, 2018 #20

    Orodruin

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    Please specify, with references. You cannot just throw a statement like this out into the blue. What issues have been solved without dark matter that it is supposed to solve?
     
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