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Could GUT be wrong (i.e unrealized in nature)?

  1. Oct 2, 2009 #1
    I understand the logic for GUT, proton decay, SU(5), SO(10) manifest at extremely high energies, as well as SUSY-extensions,


    has it been ever seriously considered that GUT is unrealized in nature? Fundamentally new physics takes over at higher energy, and therefore SM 200 Gev level energy decouples at GUT-level 15 TEV scale?

    Proton decay and mangetic monopoles and SUSY have not yet been observed. If GUT is false, how would this alter our understanding from Big Bang to particle physics?

    If GUT is wrong, are there serious alternative proposals for 10^14 GeV scale physics?
     
  2. jcsd
  3. Oct 2, 2009 #2
    Of course GUT could be the wrong idea. Just like the Higgs mechanism could be. Just like the N different extra dimensional models may be. Just like SUSY may be. Just like...

    We are living in a theory dominated world right now. Let's hope the LHC sheds the light on where to go next with the theory landscape!
     
  4. Oct 2, 2009 #3
    are there any serious alternative research programs to predict physics at the scale of 10^10gev GUT, SUSY-GUT, extra dimensional models, etc?
     
  5. Oct 2, 2009 #4

    Haelfix

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    You can write down a countably infinite amount of plausible models in that huge space between the electroweak scale and the Planck scale. 5th force models, little higgs, technicolor, preon models, you name it, its probably been done, and at many different energy scales.

    What makes GUT theories interesting is that they are typically simple conceptually, are precedented by the unification of EM and the weak force and have explanatory power for a wide range of nagging questions in particle physics. Like why the representation theory of the standard model seems so arbitrary. Why no right handed neutrino? Why are the quarks and leptons different? As well as explaining various cosmological questions.

    The phenomenology fits pretty well and is aesthetically pleasing. In a way, its somewhat of an unstated belief in particle physics... Nearly everyone believes in some sort of explanation or extra structure behind the horrible mess that is the standard model. Some sort of simplifying tale for why nature decided to mangle the low energy matter landscape
     
  6. Oct 3, 2009 #5
    Simplicity and aestetic pleasantness are important factors. Unfortunately, the only theories (to my knowledge) that can be unambigiously declared to be "simpler" than SM, are SU(5) and SO(10) non-SUSY GUTs (which seem to have been falsified by proton decay searches). Even the simplest SUSY increases the number of free parameters by an order of magnitude, and string theory inspired GUTs, based on E6 and E8, typically require an immense number of new particles somewhere near Planck scale.
     
  7. Oct 3, 2009 #6

    marcus

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    Listen to Nicolai's talk given at the July Planck Scale conference.
    http://www.ift.uni.wroc.pl/~rdurka/planckscale/index-video.php?plik=http://panoramix.ift.uni.wroc.pl/~planckscale/video/Day1/1-3.flv&tytul=1.3%20Nicolai [Broken]
     
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  8. Oct 3, 2009 #7

    marcus

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    Simplicity and economy are two of the main talking points of Nicolai's approach.
    Read my lips, no new particles :biggrin:
    No low energy supersymmetry. No large extra dimensions.
    No GUTs. Occam's razor instead.

    No new physics scales between here and Mont Planc.

    Falsifiable at LHC energy.

    The guy is a serious heavyweight---he's in charge of the quantum gravity and unification wing of the MPI. Most of his previous publication has been in QFT and string.
    If you don't have 30 minutes to listen, then glance at the slides that go with the talk.
    http://www.ift.uni.wroc.pl/~planckscale/lectures/1-Monday/3-Nicolai.pdf

    He refers to other approaches as "increasingly Baroque" and to his own program (with Kris Meissner) as "minimalistic". If they can complete this program, dot the eyes and cross the tees, then we will have something that:
    * agrees with all previous observations.
    * is testable with LHC if and when LHC runs
    * covers the range out to Planck scale without blowing up
     
    Last edited: Oct 4, 2009
  9. Oct 3, 2009 #8
    This is interesting.

    I do think this minimalistic approach would be most favorable to Sundance-Bilson braiding.
     
  10. Oct 3, 2009 #9

    marcus

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    Your reaction surprises me. Did you watch Nicolai's lecture?
     
  11. Oct 3, 2009 #10
    no but I did look at the pdf, why?
     
  12. Oct 4, 2009 #11

    marcus

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    Great! I am glad we have that in common---at least in that regard "on the same page".
    I am still surprised that you would think of spin networks---and braids---in connection with Nicolai's proposal. You don't need to explain how you arrive at that, I'll just stay puzzled:biggrin:.

    In line with your thread topic, in his lecture Nicolai emphasized the "no GUT" aspect of the proposal. Mentioned it several times. Pointed out that no evidence for GUT, protons so far refuse to decay.

    He evidently views it as an asset that their proposal just uses conventional field theory: point particles. No string, no spin network, no braid, no spinfoam. It is austere no frills. They don't have to throw in any new "made up stuff".

    No low energy supersymmetry.
    No GUT
    No extra dimensions

    I'll tell you what it reminds me of---not braid networks---it reminds me of Steven Weinberg's July CERN talk where he drew this diagram of the "stock market price" of QFT over the years from like 1950 onwards. How it repeatedly has plateaued and slowly receded (while various alternatives were tried) and then had a resurgence and shot up. And he extended the historical graph with a dotted line and explained what he thought was happening today.

    Nicolai's proposal is a perfect example of just what Weinberg was talking about. The resurgence/rediscovery of ordinary field theory. Finding that it would work where they thought new physics would enter, and that the alternatives that folks were considering weren't needed after all. An earlier example he mentioned (if I remember right) was the "S Matrix" movement.
     
  13. Oct 4, 2009 #12
    Sundance gives an accounting for spin 1/2 and 1 particles but not spin 0 or 2 nor dark matter, nor other exotic conjectured particles like axions. If SUSY is real, it's not clear whether the braiding would remain the same for the SUSY-partners.
    Since Sundance models apparently only accounts for SM particles, any new particles, esp spin 1/2 and spin 1, may violate or contradict his model. IF only SM particles exist, that would be consistent w/Sundance braiding.


    While Sundance himself connect braiding to spin networks, actually his theory doesn't commit him to it. The braids could be anything.
    Nicolai does think that a quantum gravity is needed to complete the program.
     
    Last edited: Oct 4, 2009
  14. Oct 4, 2009 #13

    marcus

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    It's probably more useful to discuss what Nicolai says in his proposal, rather than speculating about what he thinks. Don't you agree? We can't look into Nicolai's mind (or Witten's for that matter :biggrin:) so statements about what he thinks are apt to be fundamentally meaningless.

    What he actually says, in the proposal, has nothing to do with an eventual new physics that is expected to come into effect at or around Planck scale.

    What he is talking about is the huge energy-range between 100 GeV (weak) and 1019 GeV (Planck).

    He says let's change the field-theory based Standard Model as little as possible, keeping things as simple, austere, econonomical as possible, so that the field theory Standard Model will work all the way to 1019 GeV without blowing up.
    Let's do this, he says, without inventing anything new, no extra dimensions, no braids, no strings, no networks, no GUT, no supersymmetry between here and 1019 GeV.

    And we both realize that that energy is a stupendous energy to have. Enough to drive your car 100 miles. The better part of a tank of gasoline. Imagine one particle carrying that much energy. We are talking gigajoules---billions of joules. Maybe supersymmetry never, but in any case no supersymmetry until you have particles carrying a few billion joules of energy.

    Basically just move the standard model, almost unchanged, onto a different platform. In such a way that, if what he proposes is right, there is no need for new physics of any sort until Planck scale.

    That means matter would be represented just as it is today, in today's quantum field theory. In this proposal there is no room for any other representation of matter. Or? Do you see room in it?
    What it does leave open is how to represent the continuum. They need something else besides the Minkowski space of special relativity, as a platform. Today QFT is defined on Minkowski space, Nicolai says they do need to change that.

    Probably theories are not meant to be liked, they are meant to be tested---we only ask that they be conceptually economical (not overly fanciful or baroque) and testable.
    We don't know if Nicolai even LIKES the solution he is proposing (from clues like tone of voice and style I speculate that he does but) what we know is that he tells us it's worthwhile to formulate and test. It predicts a lowest lying Higgs at 207 GeV, so if it is wrong we will know soon enough. And he tells us it has a kind of minimality. It is the leanest barest-bones theory on the table that offers to get you to 1019 GeV.

    And beyond that? Well, let's get there first, there is a huge range of energy to cover, before we start speculating.
     
    Last edited: Oct 4, 2009
  15. Oct 4, 2009 #14
    In Sundance paper, he gives a way to represent the braiding for all known SM particles of spin 1/2 and 1, including charge and chirality, in the first generation. He "used" up all possible permutations. So Nicholai's proposal would be consistent w/Sundance model, or perhaps I should say that Nicholai's proposal may represent a best-case scenario for Sundance.
     
  16. Oct 5, 2009 #15
    Interesting approach, but I'd prefer my post-SM model to be even simpler than that. For one thing, he keeps the confusing zoo of Yukawa couplings between Higgs and matter fields. The whole Higgs coupling system is the most un-aesthetic part of SM.
     
  17. Oct 5, 2009 #16
    What post-SM approach is even simpler than that, and not falsified by proton decay experiments (i.e SU(5) and SO(10))?
     
  18. Oct 5, 2009 #17

    Haelfix

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    Having a vast dessert between the Planck scale and the electro weak scale is minimal, but its pretty inconsistent with expectations/ history of particle physics and almost ruled out, at least without putting more structure in.

    The hierarchy and naturalness problems go unresolved, the strong cp problem goes unresolved, dark matter goes unresolved, neutrino physics is left wide open, the assignments of the standard model look pretty arbitrary and ugly and no explanation for the free parameters is given, why do the anomalies between the quark and lepton sectors exactly cancel, why three generations and the wierd mass hierarchies, why the seemingly random scale for electroweak symmetry breaking etc etc etc? Then you get into cosmology issues, like the antimatter-matter asymetry, CP violation and baryon number violation thats flagrantly inconsistent with the SM. Why is charge quantized? Whats going on with high energy cosmic rays? What about the ridiculously tiny observed value for the vacuum energy and so on.
     
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