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Is supersymetry dead?

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  1. Apr 20, 2014 #1

    wolram

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    https://www.sciencenews.org/blog/context/it’s-too-soon-declare-supersymmetry-tragedy

    I have just been reading this and it seems to me another layer of complexion is needed to keep the theory alive.

    http://arxiv.org/ftp/arxiv/papers/1308/1308.4768.pdf


    Abstract
    The first three years of the LHC experiments at CERN have ended with “the nightmare scenario”: all tests,
    confirm the Standard Model of Particles so well that theorists must search for new physics without any
    experimental guidance. The supersymmetric theories, a privileged candidate for new physics, are nearly
    excluded. As a potential escape from the crisis, we propose thinking about a series of astonishing relations
    suggesting fundamental interconnections between the quantum world and the large scale Universe. It seems
    reasonable that, for instance, the equation relating a quark-antiquark pair with the fundamental physical
    constants and cosmological parameters must be a sign of new physics. One of the intriguing possibilities is
    interpreting our relations as a signature of the quantum vacuum containing the virtual gravitational dipoles.


    Please move if this is the wrong forum.
     
    Last edited: Apr 20, 2014
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  3. Apr 20, 2014 #2

    bapowell

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    Low energy SUSY needed to address the hierarchy problem appears in serious trouble. SUSY as a symmetry, on the world sheet of string theory or as a symmetry of space-time at higher energies, is still alive and well.
     
  4. Apr 22, 2014 #3

    Demystifier

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    If we don't want low-energy supersymmetry anymore, is there still a good motivation for styding Calabi-Yau type of compactification?
     
  5. Apr 22, 2014 #4

    bapowell

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    I'm not sure, as I'm not a string theorist. Is spacetime SUSY required by superstring theory? If not, then without the phenomenological motivation for low-energy SUSY, what would be the reason to include SUSY in your theory at all?
     
  6. Apr 22, 2014 #5

    Demystifier

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    Yes.
     
  7. Apr 22, 2014 #6
    ... How does Particle physics works w/out supersymmetry (principle)?
     
  8. Apr 22, 2014 #7
    How can anyone forget that going from bosonic string theory to a string theory which contains both fermions and bosons, one uses supersymmetry. The starting of superstrings i.e. the spinning strings was the first string theory to incorporate it. The idea of Calabi-Yau compactification requires SU(3) holonomy (in 3 complex dimensions) which is guaranteed by the existence of a constant covariant spinor which is a result of Supersymmetry. But that is another story. None of the superstrings will work without it ( hence the word super in the beginning).
    As far as the Particle physics goes, One actually needs some supersymmetry (or technicolor) to cope up with the fine tuning problem we encounter for higgs boson. If supersymmetry does not exist, then our good Standard model may lose 'Natuarality'.
     
    Last edited: Apr 22, 2014
  9. Apr 22, 2014 #8

    bapowell

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    Yes, that's worldsheet SUSY. My question was whether and how that implies spacetime SUSY.
     
  10. Apr 22, 2014 #9
    It is used in Calabi-Yau compactification as I mentioned above.
     
  11. Apr 22, 2014 #10

    MathematicalPhysicist

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    What do you mean by 'Naturality'?
     
  12. Apr 22, 2014 #11
    That is actually a remark of Sidney Coleman about the mixing of low energy scale with GUT scale (or Planck scale).
     
    Last edited: Apr 22, 2014
  13. Apr 22, 2014 #12

    wolram

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    quote


    Heavier SUSY particles do pose a problem, though. They seem to complicate the theory more than necessary, and may defy a criterion that physicists call “naturalness,” as Nathaniel Craig of the Institute for Advanced Study in Princeton pointed out in recent lectures, published at arXiv.org.

    “The march of null results suggests that we were mostly wrong about precisely how supersymmetry would appear at the LHC,” Craig writes.

    It turns out that whether SUSY lives or dies may hinge on how physicists decide to define what is natural, and whether they should insist that a theory be as simple as possible, or parsimonious. And that turns out to be a rather complicated task. To be continued

    So what is natural?
     
  14. Apr 22, 2014 #13

    Haelfix

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    It's actually false in general. String theory strictly speaking requires world sheet supersymmetry, the map to space time Susy requires a few more axioms to also be true, but it's definetely true that it makes things much simpler and most textbook models assume it.

    Matt strassler answered the ops question here
    http://profmattstrassler.com/2012/11/13/supersymmetry-dealt-a-blow

    Incidentally low energy Susy probably can't be ruled out at the LHC, even in principle. Still, most of the parameter space can be removed, and the simplest versions or subsets can be ruled out (and some already have). Generically what happens is you have to give up on either minimalism in the particle content, or you have to assume some degree of fine tuning, or you need to postulate some extra physics that acts to hide the signal from our detectors. All three of these tends to lower our posterior belief in the model.

    The problem is no one actually believes the standard model is all there is, bc the amount of independent miracles required to fit observation is many orders of magnitude worse than the scenarios above. So the real crisis is the absence of acceptable alternative ideas, and unfortunately after nearly thirty years, no one really has come up with a way out of the straight jacket, which is why a lot of 'low energy Susy is just around the corner' types keep moving the goalposts and why they are strictly speaking correct in doing so.
     
  15. Apr 23, 2014 #14

    Demystifier

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    Do you agree that in 10 flat spacetime dimensions the worldsheet susy does imply spacetime susy?

    (According to the textbooks, this is a consequence of the GSO projection, which is needed to eliminate non-physical states satisfying the super-Virasoro constraints.)
     
  16. Apr 23, 2014 #15
    I think this is a rather side effect of GSO projection which is actually needed for removing tachyonic states and maintaining some spin-statistics connection. The NSR strings actually don't have explicit susy in space-time(they use GSO projection) while the GS action preserves spacetime susy explicitly (does not use GSO projection).
     
  17. Apr 23, 2014 #16

    Demystifier

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    It may be a side effect, but the question is whether this effect is unavoidable? I think it is.
    Does anybody know a consistent formulation of string theory with world-sheet susy but without space-time susy?
     
  18. Apr 23, 2014 #17
    It will most probably then lose it's connection to our real 4 dimensional world.
     
  19. Apr 23, 2014 #18

    bapowell

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    Wait. String theory has a connection to our real 4-dimensional world? :tongue:
     
  20. Apr 23, 2014 #19

    Demystifier

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    Perhaps he meant: It will most probably then lose it's POTENTIAL to have a connection to our real 4 dimensional world.
     
  21. Apr 23, 2014 #20
    You are joking, Right? (This discussion is going sideways now)
     
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