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What if all Dark Matter searches like CDMS II remain negative?

  1. Jun 6, 2010 #1
    A couple of decades ago, there were searches for proton decay basically looking at pure water over time, and these ruled out simplest non-SUSY GUT like SU(5) and SO(10).

    There are a variety of direct Dark Matter search experiments including CDMS II CRESST, EDELWEISS, and EURECA, DRIFT, MIMAC, PICASSO, and the DMTPC, DAMA/NaI, DAMA/LIBRA and indirect searches like AMANDA, IceCube and ANTARES.

    Thus far they are negative. More sensitive dark-matter searches are coming online.

    What if all such searches remain negative?

    Can Dark matter hypothesis be continuously adjusted to always evade falsification or can a null result from these experiments falsify dark matter? By what year (i.e 2020) can we expect enough accumulated data that if there continues to be null results, the dark matter hypothesis can be ruled out?




    http://dorigo.wordpress.com/2008/03/...ms-ii-results/ [Broken]

    SUSY more unlikely by the new CDMS II results

    "What I state above is the main reason for my dislike of Supersymmetry, an otherwise quite cunning theory – maybe the only really neat idea produced in the last thirty-five years on how to extend the Standard Model to mend its shortcomings. I really hate it when I have to buy something without being able to look inside the package, but worse still is the feeling of being cheated when you are purposely prevented from doing so -the exact sensation that the mechanism of SUSY mass breaking gives me."



    "As I said right at the start, the parameter space of these models is so wide that a chunk always remains untouched. But, for those of us who did not believe in SUSY in the first place, this is just a nice confirmation."



    http://arxiv4.library.cornell.edu/abs/1005.0761 [Broken]

    SUSY dark matter in light of CDMS II results: a comparative study for different models
    Authors: Junjie Cao, Ken-ichi Hikasa, Wenyu Wang, Jin Min Yang, Li-Xin Yu
    (Submitted on 5 May 2010)

    Abstract: We perform a comparative study of the neutralino dark matter scattering on nucleon in three popular supersymmetric models: the minimal (MSSM), the next-to-minimal (NMSSM) and the nearly minimal (nMSSM). First, we give the predictions of the elastic cross section by scanning over the parameter space allowed by various direct and indirect constraints, which are from the measurement of the cosmic dark matter relic density, the collider search for Higgs boson and sparticles, the precision electroweak measurements and the muon anomalous magnetic moment. Then we demonstrate the property of the allowed parameter space with/without the new limits from CDMS II. We obtain the following observations: (i) For each model the new CDMS limits can exclude a large part of the parameter space allowed by current collider constraints; (ii) The property of the allowed parameter space is similar for MSSM and NMSSM, but quite different for nMSSM; (iii) The future SuperCDMS can cover most part of the allowed parameter space for each model.
     
    Last edited by a moderator: May 4, 2017
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  3. Jun 6, 2010 #2

    mathman

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    Until someone comes up with a plausible theory to explain the anomalous gravitational effects that are explained by dark matter, we are stuck with it as a theory. All the negative results you described indicate that we really don't know what it is.
     
  4. Jun 6, 2010 #3
    Maybe no one comes up with a plausible theory still,

    If these null results continue to pour in over time, like proton decay experiments, with increasingly sensitive searches turning in negative, will there be a point where CDM is falsified?
    I'm thinking of a historical analogy to luminiferous aether and Michaelson-Morley experiment.
     
  5. Jun 7, 2010 #4

    mathman

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    The M-M experiment appeared to falsify the existence of aether. The lack of evidence for dark matter is insufficient to falsify any one particular model. However, the gravitational effect is still there. Until a better explanation comes along we are stuck with something called dark matter.
     
    Last edited: Jun 7, 2010
  6. Jun 7, 2010 #5
    in 2010 it is, but say by 2020 or 2030?

    For dark matter to be viable, there must be a certain number of collisions to occur between dark matter particles and detector within a certain parameter space. Thus far, there have been fewer collisions than predicted in some sectors of the parameter space.

    Another historical analogy is the solar neutrino problem, only 1/3 of neutrinos were detected from the sun than predicted by theory.
     
  7. Jun 7, 2010 #6
    I don't see how the solar neutrino problem is analogous at all. In that case, we had a very detailed prediction for the number of neutrinos that should be present and the rate at which they should interact in the detectors. Furthermore, at the time it was know that the detectors being used could only detect electron neutrinos.

    With direct dark matter detection experiments, the only thing we know with even reasonable certainty is what we expect the local mass density of dark matter to be. We don't know the mass of dark matter particles; so, we don't know their number density. And, we don't know much at all about the non-gravitational scattering cross-section with matter. So, it's pretty hard to say that any amount of experimentation of this sort can totally rule out the idea of particulate dark matter.

    What we might hope to rule out is the idea that dark matter is in any way connected with the physics of the weak scale. It happens that when the dark matter mass is around the weak scale, it's cosmological relic abundance comes out right if the cross-section is of about the size of typical weak processes. So, there are quite a few models that try to fit dark matter in with whatever physics stabilizes the weak scale against quantum corrections. However, this isn't required for viable dark matter models.
     
  8. Jun 7, 2010 #7

    Chronos

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    The whole point of research like this is to parameterize the variables. We know that something that behaves much like unseen, non-interactive mass exists by virtue of gravitational effects. It may not, however, conform to other predictions under current models of fundamental forces in the universe. That is how new theories arise. I think it is still too early to indict DM as a 'conspiracy theory'.
     
  9. Jun 8, 2010 #8


    Finding 1/3 electron solar neutrinos helped falsify the conjecture of massless neutrinos.

    The non-detection of axions, magnetic monopoles and proton decays limits some GUT models like SU(5) and SO(10)

    I understand that not finding SUSY at LHC would not falsify SUSY since SUSY breaking scale could occur at some scale above LHC (although it would be a strike against SUSY as an explanation for EW stabilization)

    I suppose the properties of DM could be fine-tuned so as to evade detection in all present and future searches much as SUSY and higher dimensions and GUT's.

    What if there is no dark matter? What if dark matter is false? We would expect direct and indirect detection CDM experiments to be null and remain null. But the alternative would be to fine-tune CDM theory to evade falsification.
     
  10. Jun 8, 2010 #9

    phyzguy

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    How can you say this? Since we don't know what it is, we have no idea what the interaction rate between dark matter and ordinary matter is. All these null results do is falsify certain hypotheses for what dark matter might be - they don't falsify its existence in general. Why couldn't there be dark matter whose ONLY interaction with ordinary matter is gravitational? Then we would never detect it by any other means than its gravitational influence. That doesn't mean it doesn't exist.
     
    Last edited: Jun 8, 2010
  11. Jun 8, 2010 #10

    http://arxiv4.library.cornell.edu/abs/1005.0761 [Broken]

    SUSY dark matter in light of CDMS II results: a comparative study for different models
    Authors: Junjie Cao, Ken-ichi Hikasa, Wenyu Wang, Jin Min Yang, Li-Xin Yu
    (Submitted on 5 May 2010)

    Abstract: We perform a comparative study of the neutralino dark matter scattering on nucleon in three popular supersymmetric models: the minimal (MSSM), the next-to-minimal (NMSSM) and the nearly minimal (nMSSM). First, we give the predictions of the elastic cross section by scanning over the parameter space allowed by various direct and indirect constraints, which are from the measurement of the cosmic dark matter relic density, the collider search for Higgs boson and sparticles, the precision electroweak measurements and the muon anomalous magnetic moment. Then we demonstrate the property of the allowed parameter space with/without the new limits from CDMS II. We obtain the following observations: (i) For each model the new CDMS limits can exclude a large part of the parameter space allowed by current collider constraints; (ii) The property of the allowed parameter space is similar for MSSM and NMSSM, but quite different for nMSSM; (iii) The future SuperCDMS can cover most part of the allowed parameter space for each model.



    A future SuperCDMS can apparently detect most combination of CDM masses and interactions. If this future SuperCDMS is known to cover most of the allowed parameter space of CDM, and it and LHC comes up with a null result, will physics community continue to believe in CDM?
     
    Last edited by a moderator: May 4, 2017
  12. Jun 9, 2010 #11

    Ich

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    The abstract refers many times to the specific models of CDM it tests, but somehow you dropped that part and obviously believe they test all possible sorts of CDM.
    That's exactly the mistake phyzguy and Parlyne tried to make you aware of. With specific tests, you can exclude specific models, not the whole thing.
    That said, even if there will be no corroborating evidence from particle physics, that doesn't make the astronomical observations go away. Physicists will not like a completely undetectable particle, so they will try even harder to come up with alternative explanations or different ways to detect the particle nonetheless.
     
  13. Jun 9, 2010 #12

    phyzguy

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    The astrophysical evidence for CDM is extremely strong. Take a look at this paper:

    http://arxiv.org/abs/astro-ph/ [Broken]

    Look at FIgure 4. There are three completely independent measurements of the total matter density of the universe and how it divides into dark and ordinary matter. These three measurements could give completely different results, but in fact they all converge on the same answer for how much dark and ordinary matter there is. This answer is also consistent with other data, such as galactic rotation curves, but I don't have a reference for that handy. No competing theory (MOND, etc.) comes close to giving this kind of quantitative fit. So I think the answer to your question is, yes, astrophysicists will continue to believe in CDM, at least until someone comes up with an alternative explanation that can quantitatively explain the data. If you have an alternate explanation that is similarly quantitative, I think people will listen, but I for one will be surprised if any explanation other than CDM can fit the data.

    The question with CDM is not, "Is it there?" - it definitely appears to be there. The question is, "What is it?"

    In contrast to this data, the data in favor of supersymmetry is non-existent - there is no data at all that supports supersymmetry. This may change, but today there is no data. So if MSSM, nMSSM, etc fail to find a dark matter candidate, the physics community will just keep looking for alternate explanations.
     
    Last edited by a moderator: May 4, 2017
  14. Jun 9, 2010 #13
    Dark matter, dark energy, inflation and other aspects of the standard model are merely bolt-ons, or placeholders, until we understand more.

    In each case we are missing causal factors which might explain those phenomena, hence they are highly speculative.

    The "dark flow" recently discovered should be telling us we are missing major facets in understand the physcial universe.
     
  15. Jun 9, 2010 #14

    Ich

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    As of now, of all these dark things, I'd say the "dark flow" is the most speculative. We don't know much about the others, but at least their observational evidence is undisputed.
     
  16. Jun 9, 2010 #15
    The observational evidence is an effect of an unknown cause. For instance, the effect of the outer stars moving at the same speed as inner stars within a galaxy is an effect. We have made up a reason (placeholder) for why this is happening but there is no evidence that dark matter actually exists. We invented "dark matter" so that the standard model stays in accord with observations.

    However i concede that also applies to the "dark flow" which again is an effect we have observed.

    I dont doubt the effects of any of the "darks", but i doubt some of our bolt-on explanations which more or less just seem contrived in order to prop up the standard model.
     
  17. Jun 9, 2010 #16

    Ich

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    Yes. But the unknown's properties are more or less tightly constrained by the observations.
    That's simply not true. The evidence hints at CDM. It may be compatible with something completely different, but the easiest explanation is CDM.
    Yes. That's how it works.
    Except that I won't take the observations at face value unless they are independently confirmed.
    You say there's no evidence that there's dark matter. But you know that there are many observations which show undeniably that there is something to explain (and the DM hypothesis is not so bad in explaining these). That's not nearly as sure for the dark flow. There still may simply be nothing to explain.
     
  18. Jun 9, 2010 #17
    Ich,

    "That's simply not true. The evidence hints at CDM. It may be compatible with something completely different, but the easiest explanation is CDM."

    No, the evidence hints that something is wrong with the standard model. We have invented CDM in order to explain the anomaly. Thats not the same as there being evidence specifically of dark matter. And as of yet there is no confirmation of said dark matter, or what its made of etc...
     
  19. Jun 9, 2010 #18

    phyzguy

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    Clearly things are badly off without dark matter. The question is how to fix it. By making ONE simple assumption, that there is a significant amount of unseen matter, everything fits beautifully without needing to modify any other assumptions. Do you have any other explanation that can quantitatively explain ALL of the astrophysical data as well as the CDM hypothesis explains them? If so, I'm all ears.
     
  20. Jun 9, 2010 #19

    Ich

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    As the standard model is LCDM, I don't see how this statement could possibly make sense.

    Look, around once a week someone will drop by here, shout "DM is a stupid idea, in reality it's ...um... you know... in reality all your models are soo wrong, and now you try to cover up". These discussions always follow the same path, and i'm not inclined to go down that road again.

    So please open a new thread, bring a reference to a peer reviewed article that you think quantitatively describes the real nature of the effects we attribute to dark matter, and let's discuss it then.
     
  21. Jun 9, 2010 #20
    I'm not suggesting there is currently a better theory than CDM to prop up the standard model. My point was we have no evidence of the dark matter itself; the evidence, if you will, is inferred by missing mass according to the standard model.
     
  22. Jun 9, 2010 #21

    Then we demonstrate the property of the allowed parameter space with/without the new limits from CDMS II. We obtain the following observations: (i) For each model the new CDMS limits can exclude a large part of the parameter space allowed by current collider constraints; (ii) The property of the allowed parameter space is similar for MSSM and NMSSM, but quite different for nMSSM; (iii) The future SuperCDMS can cover most part of the allowed parameter space for each model.



    I'm alluding to the under construction SuperCDMS, which has a sensitivity to cover the parameter space of DM predicted by MSSM, NMSSM, which is in itself a substantial range of CDM space. Additionally, most big-bang models predict a certain ratio of neutralinos as Dark Matter to baryon ratio, that is within both SuperCDMS and LHC reach.

    A non-observation of neutralinos at LHC and SuperCDMS would falsify such Big Bang CDM synthesis.

    As with magnetic monopoles, proton decay, SUSY-breaking scale, extra dimensions I don't deny it could be possible to fine-tune CDM to evade bounds set by LHC, SuperCDMS and all current and projected direct and indirect detection limits.
     
    Last edited: Jun 9, 2010
  23. Jun 9, 2010 #22
    The parameter space for all CDM models is not the same thing as the parameter space for MSSM, NMSSM, or nMSSM neutralino dark matter. Dark matter can have non-SUSY origin.
     
  24. Jun 9, 2010 #23
    fair enough. SuperCDM is just one direct line, there are other research groups and indirect lines that are also attempting CDM detection running concurrently.

    CDMS II had 2 candidate events with 25% probability, far from 2-sigma significance.

    SuperCDMS 25 kg Experiment
    http://titus.stanford.edu/public/brochures/SuperCDMS_A.pdf

    #
    File Format: PDF/Adobe Acrobat - View as HTML
    Need 1 x 10-4 evt/kg/day for SuperCDMS 25 kg. • From surface contamination (e- ... We pursue the R&D for beyond SuperCDMS 25 kg phases: • 150 and 1000 kg ...
    cosmology.berkeley.edu/inpac/.../SuperCDMS_INPAC2007.pdf - Similar
    # [PDF]

    The SuperCDMS proposal for dark matter detection
    File Format: PDF/Adobe Acrobat - Quick View
    by DS Akeriba - 2006 - Cited by 25 - Related articles
    Dec 27, 2005 ... WIMP-nucleon cross-sections in the range 10À46 À 10À44 cm2, we propose SuperCDMS, which would take advantage of a very deep site. ...


    [PDF]
    SuperCDMS Development Project
    File Format: PDF/Adobe Acrobat - Quick View
    SuperCDMS is bold program to extend the sensitivity for dark matter .... SuperCDMS Development Project (request start FY2006) ...
    www.fnal.gov/directorate/program.../Cabrera_April2005PAC.pdf[/URL] - Similar
    cosmology.berkeley.edu/preprints/cdms/LTD11_paper_Brink.pdf - Similar
     
    Last edited by a moderator: Apr 25, 2017
  25. Jun 10, 2010 #24
    You hinted at it when you said: "Why couldn't there be dark matter whose ONLY interaction with ordinary matter is gravitational? Then we would never detect it by any other means than its gravitational influence."
    In that case the explanation would point to a modification of our understanding of gravitational influences in galactic and supragalactic scales; and I don't mean MOND but I'd guess something more intrinsically related to spacetime curvature.
     
  26. Jun 10, 2010 #25
    Hi, I'd be interested in the article but the link isn't working.
    Cheers
     
    Last edited by a moderator: May 4, 2017
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