Assorted Links

Some assorted things I’ve run across recently that may be of interest:

Talks from the annual meeting of the SLAC Users Organization.

A dialogue between Barry Mazur and Peter Pesic about imagination and mathematics.

An Op-Ed piece in today’s New York Times by my colleague Brian Greene called That Famous Equation and You.

Some sensible comments by John Baez about string theory.

A survey of the state of string field theory by Leonardo Rastelli.

A “description of some important issues in supersymmetry and string phenomenology” entitled Twenty-five Questions for String Theorists. The authors think these questions may have answers that will help connect string theory and phenomenology, although this seems to me unlikely. Serkan Cabi also has some comments on this paper.

An article about Feynman by Freeman Dyson in the latest New York Review of Books.

A talk about theoretical physics in the Netherlands.

Update: One more, a report by Paul Cook on an interesting talk by Roman Jackiw.

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11 Responses to Assorted Links

  1. Arun says:

    John Baez wrote (from the URL provided)

    The saddest the LHC could find is a complete
    confirmation of the Standard Model, Higgs particle and all. ┬áThen we’re
    back to pondering these puzzles without benefit of extra clues.

    Could the absence of extra clues be a clue? The good thing would be that one doesn’t have to wait for the LHC to start working on that. :)

  2. Wolfgang says:

    I have to assume that in the current environment any deviation from the standard model observed at the LHC would be (initially) understood as indication of supersymmetry.
    A good example was the deviations recently observed for g-2 experiments.

  3. After two years in the swamp, my position is that we already have extra clues. Wasting the “single self-advertisment post” rule that Woit gave time ago, here come three examples from my own:

    hep-ph/0405076 (and related preprints) indicates that a “lamb balance” could be hinting us the points where massive particles are.
    hep-ph/0505220 (and Dr. Koide’s work cited there) hints that quarks and leptons should be, if not composite, supersymmetric to diquarks and mesons.
    hep-ph/0507144 hints that the above is related to the properties of the Z0 particle. Note also that the decay of Z0 has properties usually derived from GUT theories

    If LHC comes with confirmation of standard QFT (eben with non-minimal higgs), I’d hopw theorist to start looking seriously for missing extra clues. Also, at these times the LEP colaboration files should already be open in the field for everyone to explore, should them?

  4. John Baez says:

    Wolfgang writes:

    I have to assume that in the current environment any deviation from the standard model observed at the LHC would be (initially) understood as indication of supersymmetry.

    Yes, I worry about that too, but I believe (and hope) that the experimentalists are more careful about these things than the superstringers.

    I recently participated in a PhD oral exam of a physics student who is building detectors for the LHC. He spoke about signatures of nonminimal Higgs bosons. One of the physicists on the committee noted that there are ways to tell the difference between various kinds of nonminimal Higgs bosons and the specific sort which appears in the MSSM (the minimal supersymmetric extension of the Standard Model). So, while superstringers will initially proclaim any hint of a nonminimal Higgs as evidence for the MSSM and “therefore” as evidence for string theory, experimentalists are less likely to jump on this bandwagon without good evidence.

    The student also claimed that among the 105 (!) adjustable parameters in the MSSM, only a couple affect the behavior of the Higgs. So, it may not be quite as much of a morass as I’d thought. I’m still a bit concerned, though.

    You probably know the old saying:

    With 7 parameters you can fit an elephant.

    I had worried that with a 105 adjustable parameters, even the LHC short-circuiting and exploding could be explained by the MSSM.

    People interested in this issue may enjoy reading about a computer program called Fittino that’s supposed to do a best fit of 24 MSSM parameters based on LHC data.

  5. Aaron Bergman says:

    There are not 105 adjustable parameters in the MSSM. There are ~100 (109 is the number that comes to mind, but whatever) adjustable parameters in the soft susy breaking lagrangian. One expects many relations amongst them from however susy ends up being broken.

  6. woit says:

    But until someone figures out what the susy breaking mechanism is, John is right that there are at least around 100 adjustable parameters. The idea that SUSY exists in the real world and that SUSY is broken by some physics that can be parametrized by a small number of parameters looks more and more like wishful thinking. People have been trying to do this for more than 25 years, and there still is no theoretically convincing model for supersymmetry breaking, or even a shred of experimental evidence.

  7. Aaron Bergman says:

    I’m curious about “more and more” there? SUSY itself has some trouble with the Higgs mass, but SUSY breaking looks just as ugly as it always has. I don’t see any change there.

    Regardless, the weak susy breaking lagrangian is a phenomenological lagrangian. There are plenty of real problems with susy, but the number of parameters there isn’t one of them.

  8. woit says:

    By “more and more” I mean that, besides the increasing amounts of fine-tuning needed, as people have learned more and more about supersymmetry breaking it’s become more and more clear what a gory business it is. 25 years ago one could have thought that this was just because there hadn’t been enough work on the subject, so people hadn’t had time to discover a simple way to break supersymmetry that would lead to some predictions. As time goes on, it get more and more clear such a thing probably doesn’t exist.

  9. John Baez says:

    Aaron Bergman writes:

    There are not 105 adjustable parameters in the MSSM. There are ~100 (109 is the number that comes to mind, but whatever) adjustable parameters in the soft susy breaking lagrangian. One expects many relations amongst them from however susy ends up being broken.

    Maybe so (or maybe not). But, I was talking about experimentalists with the the practical chore of looking for hints of supersymmetry in the LHC data. Unless someone figures out some relations before data analysis begins (optimistically around 2008), these folks have about 100 adjustable parameters to fiddle with. And they’re busy trying to figure out how.

    I’m no expert on this stuff. I got the figure of “105″ from various including the “Fittino” program I mentioned – check ‘em out! This figure apparently excludes the roughly two dozen parameters already built into the Standard Model.

  10. One of my interests last year has been to try a measure of information content beyond “free parameters”. Of course I haven’t got any succes. The only reasearch I am aware of comes from a bayesian statistics, I.J.Good. The point is that the act of selecting a theory, or a method of symmetry breaking, or a special set of islands, can also be considered as information you input in, and it should be counter between the parameters if there are in the town other theories (or symmetry breaking patterns, or sets of islans) equally sound.

  11. Arun says:

    Hmmm:
    http://arxiv.org/abs/hep-ph/0412012

    It is impossible to determine all 105 possible parameters of L_MSSM simultaneously. Therefore, assumptions on the structure of L_MSSM are made. All complex phases are set to 0, no mixing between generations is assumed and the mixing within the first two generations is set to 0. Thus the number of free parameters is reduced to 24 (MSSM-24).

    24 doesn’t seem so bad.

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