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B Dark matter variations on Earth

  1. Sep 1, 2017 #41

    Drakkith

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    QED does model electrostatic interactions using virtual photons though, and Feynman diagrams incorporate both real and virtual particles if I remember correctly.
     
  2. Sep 1, 2017 #42

    ohwilleke

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    A field is just photons. If there is nothing to transmit electromagnetic interactions, there is no electromagnetism. Coulomb's law absolutely requires photons in QED.
     
  3. Sep 1, 2017 #43
    Do you see any from a static charge? Where are they? What frequency? Virtual perhaps but ... long story ...
     
  4. Sep 2, 2017 #44

    mfb

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    Photons have to be possible to have static fields in QFT, even if there are no photons flying around.
     
  5. Nov 15, 2017 #45
    What if there were dark matter that interacts only with photons and concentrated in the sun and it doesn't interact with any other particles.. does it mean this dark matter species doesn't interact with the weak force but only gravity and with photons.. what are these called then and isn't there any paper that mentions this?
     
  6. Nov 15, 2017 #46

    Drakkith

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    Please stick to real science and avoid speculation such as this. We can't hope to answer every "what if..." scenario that people come up with.
     
  7. Nov 15, 2017 #47
    I mean why does dark matter obey the weak interaction.. does it really interact with the weak force? Why not just gravity?
     
  8. Nov 15, 2017 #48

    Drakkith

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    As far as we know, it doesn't. It only interacts via gravity.
     
  9. Nov 16, 2017 #49

    mfb

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    We know it doesn’t interact with photons, otherwise we would see it.
    For particles that interact only via gravity it is unclear how they could have been produced in the right amount in the early universe.
     
  10. Nov 16, 2017 #50
    I thought WIMP interacts via the weak force.. i thought anything that comes from Supersymmetry should interact at least the weak force.. but if it only interacts via gravity.. how come experiments reported WIMP null results when they can't be detected except by gravity?
     
  11. Nov 16, 2017 #51

    mfb

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    By definition, yes (WI in WIMP). That doesn’t mean dark matter has to consist of WIMPs.
    Additional particles don’t have to participate in the weak interaction, it is just likely.
    Null results of detectors looking for weak interactions are perfectly consistent with particles with no weak interaction.
     
  12. Nov 16, 2017 #52

    ohwilleke

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    Particles with no weak, strong or EM interactions are not only perfectly consistent with the non-detection of dark matter in direct detection experiments and the non-detection of DM at the LHC. They are also consistent with the absence of any compelling DM annihilation signature. So, while non-detection of DM in those channels is parameter bounding for DM theories, it certainly doesn't rule out DM that is "sterile" (i.e. that only interacts via gravity) or DM that only interacts with other DM in addition to gravity.

    The trouble is that the amount of correlation between inferred DM distributions and baryonic matter distributions is too tight to be explained by gravity alone and the shape of the DM distributions aren't what we would theoretically predict if DM was truly sterile or only interacted with other DM. So, truly sterile DM or DM that only interacts with other DM isn't enough to explain the phenomenology.

    This leaves you looking for a fifth force that predominantly governs DM-ordinary matter interactions (and possibly also DM to DM interactions), such as the paper described below, in a dark matter particle theory.

    Andres Olivares-Del Campo, et al., "Dark matter-neutrino interactions through the lens of their cosmological implications" (November 14 2017).
     
  13. Nov 17, 2017 #53
    May I know what this "correlation" you were referring to that indicates the amount of correlation between inferred DM distributions and baryonic matter distributions is too tight to be explained by gravity alone? Some references directly about it perhaps? Thank you

     
  14. Nov 17, 2017 #54
    It says it solves some problems for CDM also it can simulate on large scales.

    But in general it doesnt seem to me a perfect candidate to understand the general description of CDM. As ohwilleke pointed out we need a new model and maybe even a new force.
     
    Last edited: Nov 17, 2017
  15. Nov 18, 2017 #55

    ohwilleke

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    Some references can be found in thIs post. I don't specifically mention it there but collisionless bosonic dark matter models also don't work.
     
  16. Feb 5, 2018 #56
    Just for sake of understanding of your "fifth force that predominantly governs DM-ordinary matter interactions (and possibly also DM to DM interactions)", supposed you had a dark matter jacket that somehow got binded to your body and the dark matter jacket weights 50 lbs and you weight 100 lbs.. what would happen if you put yourself in a weighting scale. Would it register 150 pounds or 100 pounds? I know the dark matter jacket won't affect the weighing scale directly and it won't be pull down because the earth won't attract it.. so I guess it can just cause a drag in your body when you run.. can this drag be measured? In cosmological setting.. what are the results of attempts to measure this drag?
     
    Last edited: Feb 5, 2018
  17. Feb 5, 2018 #57

    Drakkith

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    It would certainly be attracted to the Earth, as dark matter interacts gravitationally with normal matter. If you could somehow attach this jacket to yourself you would find that you weighed more. There would be no drag though, as that requires an EM interaction, which dark matter doesn't have.
     
  18. Feb 5, 2018 #58
    Hmm... don't they make weighing scale in the labs that can measure the dark matter flux by coupling using the fifth force with dark matter moving all around.. it should register different readings.. shouldn't it?
     
  19. Feb 5, 2018 #59
    Are there dark matter candidates which don't contain mass but only pure energy (which can still interact with gravity)?

    If a particle has no mass (like photons) it moves at the speed of light... but photons have energy... I mean.. if dark matter contains no mass but only energy.. should it move at speed of light too?
     
  20. Feb 6, 2018 #60

    ohwilleke

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    A massless particle moves at the speed of light which is inconsistent with dark matter which has sub-relativistic speeds (i.e. it is 'warm" or "cold" dark matter, not "hot" dark matter) if it exists in the form of a particle, although massless particles could, in principle be confined in a massive composite particle (e.g. a "glueball"). For the same reason, ordinary neutrinos cannot be dark matter because they are too "hot" which is to say that their average velocity is too large.
     
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