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Why would a Susy signal have been bad news for the Loop program?

  1. Sep 2, 2011 #1


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    This may seem like a naive question to some people.
    I had always heard that Lqg can easily incorporate supersymmetry---that if there were any evidence of it, putting it into the theory would be straightforward.
    This goes way back, to papers I read in 2003-2005. Not sure exactly which, but it was a "well known" commonly accepted truth.

    There was a similar statement about Lqg in higher dimensions that I think I recall seeing in a paper by Lee Smolin, but I don't know how widely accepted that was.

    Anyway Carlo Rovelli recently remarked that the failure to see signs of Susy at LHC was GOOD NEWS for Lqg. I think that means that simply means that a Susy signal would have been bad news. So we can be happen one has not been seen so far.
    The question is WHY?

    At first I thought this must mean that the recently (2007-2010) developed new formulation of Loop Gravity presented some obstacle to supersymmetry, at least at some level.
    So then obviously seeing Susy could be a setback for the program.

    But I have not gotten any indication that this is right. So I must retract on that!
    Apparently if there were some indication that nature is supersymmetric the Loop program could make a smooth transition. This was what Lee Smolin's recent post here would seem to imply. Not a serious setback at all.

    However then why would a Susy signal at LHC have been bad news for the Loop program?
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  3. Sep 2, 2011 #2


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    Good news means that it wouldn't be reasonable for funding agencies to concentrate on string research. It would be easier to convince them to explore other venues, including LQG.
  4. Sep 2, 2011 #3


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    You could be right. It never has been reasonable for them to concentrate as heavily as they have in the Usa. At least the ESF (European Science Foundation) has supported a range of different QG approaches in Europe---and it has been enormously fruitful!

    But the 5-year charter of the ESF's quantum geometry/gravity network runs out this year.
    Unless it is renewed, Europe will not have John Barrett's QG agency supporting things like the Zakopane school, workshops, and the 2011 Zurich conference.

    A Susy "no-show" helps to teach the lesson that string is not "the only game in town".

    So that could be good news both for funding in Europe and for any aspiring loopers in the Usa (we seem to have some at UC Berkeley, so I know they exist :biggrin:).

    But I thought that something else was meant by the good news---something besides practical day-to-day stuff like funding and jobs. I could have been mistaken.
  5. Sep 3, 2011 #4


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    I wouldn't say that SUSY itself is a problem for LQG, but of course SUSY would be interpreted as a signal of strings and/or SUGRA. And that would be a problem!

    Thiemann is working on LQG in arbitrary dimensions including SUGRA. There are some special features of SL(2,C) used in the LQG approach which are not available in other dimensions, of course. So Thiemann tries to get rid of these restrictions to 4-dim.

    In addition there are not only technical but funding aspects as well:-)
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