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Featured I Dark Matter and who will discover it first?

  1. Jun 12, 2017 #1
    While the subject has been talked about to death by many a researcher, who will discover the first dark matter scientific paper that will prove beyond theory that describes it in detail. The real discoverer will undoubtedly be the hero of physics, astrophysics, and cosmology and be awarded surely the Nobel Prize for science. Any notables that today seem on the cusp of it's discovery?

    My takes:
    Lisa Randall
    Richard Massey
    George Efstathiou

    Among others...
     
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  3. Jun 12, 2017 #2

    mfb

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    The discoverers of dark matter particles will be groups of experimental physicists.
    There are many viable theoretical models of dark matter, and we need experimental results to figure out what we have in nature.

    Groups have a poor track record of getting Nobel Prizes. See the Higgs boson.

    Zwicky, Oort and Kapteyn would be potential Nobel Prize candidates (as first scientists to find evidence of dark matter), but they are dead. Vera Rubin was a candidate for a long time, but died in 2016. Kent Ford is still alive (86) but I would be surprised if he gets the prize.
     
    Last edited: Jun 12, 2017
  4. Jun 12, 2017 #3
    Cusp of it's discovery? It's been more than 80 years since Fritz Zwicky first proposed the idea and the LHC just verified the stunning predictive accuracy of the standard particle physics model, so your optimism seems a tad premature. :)
     
  5. Jun 13, 2017 #4
    I hate to disappoint you (us), but as of now there is (almost?) zero experimental evidence of DM. LUX experiment, at its maximum sensitivity (for now), failed (last summer) to detect even one single particle of Dark Matter:
    http://phys.org/news/2016-07-world-sensitive-dark-detector.html

    I think there will be a new LUX (possibly with even higher sensitivity), and I am not aware of the progress on the subject ever since.
    But what happens if they still discover nothing? What will be the fate of Dark Matter then? Experiment is the ultimate judge of theories ...
     
  6. Aug 8, 2017 #5
    It was only last summer when the high resolution LUX experiment failed to detect WIMP's of dark matter. This year (last May) XENON1T beats LUX in sensitivity but still did not detect any dark matter candidate:

    https://phys.org/news/2017-05-xenon1t-sensitive-detector-earth-wimp.html

    For the results see directly the original paper (reports consistent with background only):

    First Dark Matter Search Results from the XENON1T Experiment.
    https://arxiv.org/abs/1705.06655

    From what I heard, a new hope now could rely on the follow-up project of LUX, the LUX-ZEPLIN, with its colossal detector size (around 90 times more sensitive than LUX).
    Failing of that also ("knock on wood" ... !?) however won't bode well for anyone getting a nobel prize (for Dark Matter), or for the future of Dark Matter itself! ...

    I guess we'll find out.
     
  7. Aug 8, 2017 #6

    mfb

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    The XENON1T result was based on a single month of data-taking, they'll improve that limit quickly.
    LUX-ZEPLIN (2020+) and XENONnT (2019-2020+) will both improve it again. DARWIN aims for a start 2023, and it will either find dark matter or improve the exclusion limits to the neutrino background.
    Currently the experiments double the sensitivity roughly every year. I wrote a bit more about the searches in this Insights article.
     
  8. Aug 8, 2017 #7
  9. Aug 8, 2017 #8

    ohwilleke

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    There is no evidence of dark matter particles that interact via any of the three Standard Model forces (electromagnetic, weak, strong) over a mass range that extends from at least 1 GeV to 1000 GeV based upon direct dark matter detection experiments and the LHC. Moreover, astronomy observations strongly disfavor heavier dark matter candidates. And, collisionless cold dark matter is also pretty strongly disfavored with a possible exception in the keV mass range.

    There is a constant flood of new astronomy observations that continue to tighten (and indeed come close to overconstraining) the parameter space for dark matter, but we can be reasonably confident that direct detection of dark matter is not going to happen any time in the next thirty year or more, if ever. Dark matter makes neutrinos look like bulls in China shops.
     
  10. Aug 8, 2017 #9

    mfb

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    What exactly rules out a possible discovery by XENON1T and its follow-up experiments?
     
  11. Aug 9, 2017 #10
    A)
    It is necessary for this (below) timetable etc. to be followed first, before anyone can conclude anything ... :
    Unless something else conclusive happens before then to prove, disprove or totally reject DM etc.

    In the meantime, I'm anxious waiting for those experiments and results! ...

    B)
    I am not aware, ... other than what you cited.
     
  12. Aug 9, 2017 #11

    ohwilleke

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    Some of sub-GeV mass range is also excluded by direct searches at the LHC. The latest LHC results even strictly limit Higgs channel dark matter candidates.

    Equally important, if the kind of dark matter that these direct dark matter detection experiments are looking for exists, it would behave in a very particular way that would be reflected in its behavior that can be indirectly observed with astronomy observations such as rotation curve and lensing measurements of inferred dark matter halos. The behavior of the kind of dark matter sought is also the single most well modeled scenario in N-body simulations of dark matter.

    For example, generically, dark matter of the kind that could could be found by XENO1T and its follow-up experiments would generate the wrong shaped/wrong density distribution halos (something that baryonic feedback mediated only by gravity and weaker than neutrino weak force interactions can't alleviate), would not be able to reconcile measurements based upon rotation curves and those based upon lensing, would not track baryonic matter distributions as tightly as observation indicates, would not generate particle velocities sufficient to give rise to the number of observed high velocity galactic cluster systems of which the Bullet Cluster is an example, and would generate more small scale structure (such as satellite galaxies) than is observed by astronomers.

    Some of these problems are summarized in a literature review supported by references from this preprint (references fully described in end notes in the original, paragraph breaks inserted for ease of reading in this non-typeset format):

    (At the large scale structure/CMB/lamda CDM scale, the Standard Model of Cosmology is insensitive to the details of dark matter particle properties from wark dark matter in the roughly keV scale all of the way up to brown dwarf sized MACHOs and stellar black holes, so long as it is very nearly collisionless.)

    The noise created by the neutrino background which currently can't be effectively filtered out, undermines the methodology of these experiments long before they have enough resolution to detect warm dark matter that might behave differently in the respects described above.
     
    Last edited: Aug 9, 2017
  13. Apr 1, 2018 #12
    While looking for Dark Matter on earth, in the meantime, a group of astronomers have discovered a galaxy with no dark matter at all! ... Or have they?
    https://physicsworld.com/a/galaxy-devoid-of-dark-matter-puzzles-astronomers/

    However, note that that can be proof by itself that DM exists ... , providing the data is correct and no other plausible explanation can be found ...
     
  14. Apr 1, 2018 #13

    phinds

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    There's already a thread on this:
    https://www.physicsforums.com/threads/galaxy-with-no-dark-matter-ngc1052-df2.943345/
     
  15. Apr 2, 2018 #14
    Sigh! I'm reminded of the drunk searching for his keys under a streetlight. He hadn't dropped them there, but the light was much better.

    How much dark matter is in the solar system? To make the question specific, inside the orbit of Neptune.

    There may be some, but on the order of a few kilos. How do we know that? NASA, ESA and others have been sending spacecraft all around the solar system--and beyond. If there was any significant amount of dark matter around, the trajectories of the spacecraft would have been changed. Yes, the acceleration might be on the order of a nanometer per second squared--but such effects on spaceprobes have been studied. Remember the Pioneer anomaly, caused by differential heat radiation from the RTG? There might be dark matter trapped by gravity in the center of planets or the sun, but even that is unlikely. Models of the interior of the Earth from seismic waves don't leave much wiggle room.

    Let me propose a dark matter particle that has a mass on the order of neutrinos, and interacts with photons and other matter about as rarely. What happens? The rate of interactions and the relative masses mean that it wouldn't show up by fuzzing light from other stars and galaxies. It might have that effect on radio waves, but the expansion of the universe means that radio waves from far away arrive at Earth after being red shifted. So only the interaction during the last few billion years would be noticeable. ;-) Around galaxies and galaxy clusters, there should be a point where average interactions with photons (and neutrinos!) is balanced by the gravity from the galaxy or cluster.

    Don't use Occam's Razor to conclude that okay, dark matter is made of neutrinos. Cosmology calls for a lot more DM than neutrinos in the early universe by mass. My best guess would be a particle in the kev range, emitted only during high-energy particle interactions. It might not be the right answer, but I know that the right answer will not be found by looking under the streetlight.
     
  16. Apr 3, 2018 #15

    mfb

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    The expected amount of dark matter is comparable to a small asteroid. Much more than a few kilograms, but still way too small to notice it with spacecraft. If spacecraft would have found a deviation it would have indicated that our dark matter models are wrong.
    Seismic waves don't constrain the amount of dark matter inside Earth in any relevant way.

    Neutrinos can be considered a part of dark matter, but they cannot clump on the scale of galaxies, nothing like them can be a large part of dark matter. Axions are a possible model with small mass.
    In that case it wouldn't be dark matter.
    You can't have an interaction that is selective to wavelengths. In addition, radio waves have been around the whole time.
    As a first step, you should learn how the key we are searching looks like.
     
  17. Apr 3, 2018 #16

    ohwilleke

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    Just to embellish slightly on this part of your answer, not only is it comparable to a small asteroid (which as you note, still isn't much), it would be more of less evenly dispersed through the entire volume of space in that part of the the solar system. So, at a solar system level, there would be observable effects only to the extent that there was inhomgenity in the dark matter distribution. The bottom line is the same: it is way too small to notice it with space craft. But, because it would be so broadly and evenly dispersed, it would be multiple orders of magnitude harder to notice than a simple single small asteroid would be.
     
  18. Apr 3, 2018 #17

    Chronos

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    If the dark matter density profile of the solar system mimics that believed of galaxies, it may help explain why direct detection has proven so challenging. This does not, however, necessarily spell doom for the current generation of experiments.
     
  19. Apr 4, 2018 #18

    mfb

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    It does not. Dark matter doesn't clump on scales that small - that would need a strong interaction that it cannot have.
     
  20. Apr 4, 2018 #19

    Chronos

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    I would not call ~0.4 Gev/cm3 [the estimated DM density at the suns vicinity in the MW per https://arxiv.org/abs/1212.3670 ] very clumpy. That works out to about 8 x 10-25 gm/cm3 on average. Assuming the density peaks at the sun similar to the DM density at the MW core and falls off sufficient to meet this calculated average for the volume encompassed by the Oort cloud, looks fairly plausible to me.
     
  21. Apr 4, 2018 #20

    mfb

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    It does not. That's exactly what my post said.
    "Clumping" is a statement about the distribution, the average density somewhere has nothing to do with it. The density is very uniform at the scale of the solar system.
     
  22. Apr 4, 2018 #21

    Chronos

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    Permit me to clariy, While the average DM density is indeed irrelevant. DM density peaks [note the caveat: assuming they exist] may be within detection limits of the latest generation of DM experiments
     
  23. Apr 4, 2018 #22

    mfb

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    To get strong localized peaks you need some relevant interaction apart from gravity - but such an interaction would also make a disk out of dark matter, contrary to the halo we have.
     
  24. Apr 5, 2018 #23

    Chronos

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    Dark matter density can be more complicated than you are apparently suggesting, as discussed here: https://arxiv.org/abs/0810.0277,
    Evolution of the Dark Matter Phase-Space Density Distributions of LCDM Halos.
     
  25. Apr 5, 2018 #24

    mfb

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    Where exactly are they discussing scales as small as planetary systems?
     
  26. Apr 5, 2018 #25

    Chronos

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    Understood and agreed. This, https://arxiv.org/abs/0810.0277. is not the ideal reference for discussion of local DM density. While It does capture some of the nuances of small scale DM density variation, the smallest scales specifically addressed are of MW size order, not solar system size subhalos. To that end, I suggest this one as more suitable; https://arxiv.org/abs/1404.1938, The Local Dark Matter Density. I feel it offers real hope the current generation of direct DM detection experiments have potential to succeed - depending, of course, upon how strict a standard of proof desired. For those with 'pin it to a display board and hang in a museum' mentality, a little LHC magic is probably needed. Just a brief comment here. Since a fairly popular belief is that DM is born cold, LHC may be a long shot. For the less demanding, even GAIA may be persuasive; https://arxiv.org/abs/1506.00384, The difficulty of measuring the local dark matter density.
     
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