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Beyond the standard

  1. Feb 3, 2006 #1

    wolram

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    Model, well i doubt if any one can give a clear discription of what that is, to me everything is up for grabs, or is there some definitive information out there unknown to me, if any long suffering member can tell me where standard meets non standard it would be much appreciated.
     
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  3. Feb 3, 2006 #2

    selfAdjoint

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    Theories that could extend the Standard Model.

    Level 0: Standard Model with or without Higgs mechanism. See this thread on the particle physics board.

    Level 1. Grand Unified Theories (GUTS). Bigger gauge groups to eliminate some of the 19 or so parameters that have to be put in by hand in the SM. This enterprise constrained by the Coleman-Mandula theorem which says that as long as you stay with the methods used in the SM math, gauge theory and such, you don't get any really new physics beyond the SM.

    Level 2. Supersymmetry. This is a new assumption that evades the Coleman-Mandula theorem Fermions and Bosons now form a symmetry and every particle of one type has a partner of the other. Fermionic partners of bosons have names that end in -ino, as in photino, gaugino. Bosonic partners of fermions have names that start with s-, as in selectron. The simplest supersymmetric model that contains the SM is called the Minimum Supersymmetric Model, or MSSM. Recent work at Tevatron has greatly constrained the MSSM, requiring it to be very finely tuned in order to agree with, e.g. the new mass for the top quark.

    Level 3. Strings, superstrings, branes, M-theory, string field theory. Any or all. Frequently they try to produce the MSSM by modeling with strings and branes. Some models look pretty close but the whole enterprise has more than a whiff of epicycles in my opinion.

    Level 3.5. Lisa Randall's new warped brane model. Has the defects of the above but claims to predict a testable result that can be seen at the LHC when it's up and running.

    Level 4. Quantum gravity. Various approaches. Just now getting into matter after a long stretch of trying to get gravity to quantize right. Some of them can do particles in toy models but I don't think any of them have a convincing rep of the SM.
     
    Last edited: Feb 3, 2006
  4. Feb 3, 2006 #3

    marcus

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    ho ho that's the spirit wolram
    total bemused skepticism is what makes Physicsforums great!*
    long time no see and welcome back if only for an instant

    *one of the things, at least, there's also the praiseworthy efforts made here to sort it all out
     
    Last edited: Feb 3, 2006
  5. Feb 3, 2006 #4

    wolram

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    For an instant? i am sorry Marcus but i will be a thorn in your side until i have some answers, that is what i came here for:rofl: you and i know the math means little to me, i just need a few well informed people to tell me what the U is alll about:smile:
     
  6. Feb 3, 2006 #5

    marcus

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    aye Wolram, that do we all!

    it's somewhat about sex, I think, though the cryptic crossword Harper's runs a close second
     
    Last edited: Feb 3, 2006
  7. Feb 4, 2006 #6

    wolram

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    Thankyou SA, Marcus, may be it is not long now for some more news ?
     
  8. Feb 4, 2006 #7
    A question: What are the 'limitations' and 'problems' anyway of the standard model that it needs replacing?

    All the arguments I've heard for proposing string theory etc was 'as it is interesting'. True, but quite unpragmatic it seems to me.
     
  9. Feb 4, 2006 #8

    selfAdjoint

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    The SM AFAIK has no problems as far as its predictions go. Theorists are working their way up the loop structure in perturbative calculations (the answers come as an infinite series in the Feinmann diagrams of the interactions. Perturbation theory can only do the first few terms.). They are only up to two-loop so far (by contrast, QED calculators are past four-loop and working on five-loop). But the SM predictions as far as they go and up to their expected uncertainty range are confirmed in experiments at the accelerators.

    What bugs physicsts about the SM is the number of undetermined parameters it depends on. It would be nice to have a theory that derived these from first principles. And of course there's the gravity issue. Also the Higgs mechanism is rather delicate and no experimental evidence of it has turned up so far, so what the LHC sees after 2007 will make or break that, and without that the standard model would have to undergo major mods, at least.

    So there's reason enough for people to study beyond it.
     
  10. Feb 4, 2006 #9
    What about the lack of being mathematically well defined, infinite dimensional volume elements, renormalization to get rid of infinities, and all that? It would be great if you could give us a few words on how well defined the theory is and how extented theories might fix it. Keep going, you're doing great. Thanks.
     
    Last edited: Feb 4, 2006
  11. Feb 4, 2006 #10

    Kea

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    Hi Mike2

    Actually, physics doesn't really care about all that, except that a better mathematical understanding would almost certainly tell us more about those annoying parameters. Developing physical theories have often had an association with developing mathematics, which the physicists usually do rather badly.:smile:
     
  12. Feb 4, 2006 #11

    Kea

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    The point is not that the SM needs replacing, but that we need physics that goes beyond the SM in order to explain many things that we actually see, eg. WMAP data, or don't see, as selfAdjoint has pointed out.
     
    Last edited: Feb 4, 2006
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