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Peter Woit comments on technicolor models (and my take on string theory)

  1. Oct 28, 2007 #1

    "Comment on Technicolor/Extended Technicolor Models
    October 26th, 2007"

    very brief excerpt "I would like to respond to Eric’s recent comment on Oct. 23 in which he said that “technicolor models were..eventually rejected due to some serious shortcomings. Namely, in order to generate fermion mass hierarchies for the SM fermions, one ends up with serious problems with FCNC’s.” and that these theories “led to a plethora of technimesons, for which there is absolutely no evidence.”.

    Josh1 and other string theorists reading this, If LHC provides experimental evidence for technicolor, and no experimental evidence for higgs/SUSY, can string theory account for such a result?

    this is my take on string theory:
    If LHC provides experimental evidence for technicolor, and no experimental evidence for higgs/SUSY, such a null result would be very difficult to account for in string theory since 1 original argument of SUSY is a solution to the hierarchy problem created by the higgs field, with predictions of lightest mass SUSY particles around the EW-scale (200GEV). I agree with the usual disclaimer that it's possible SUSY is a fundamental symmetry of nature, broken above the EW scale, and beyond LHC collision energies, and I suppose there could be higgless models of string theories, but I would suggest the possibility that perhaps fundamental physics is not described by string theory in this experimental scenario.
    Last edited: Oct 28, 2007
  2. jcsd
  3. Oct 28, 2007 #2
    Technicolor would be great, in a sense, because technicolor is dual to Randall-Sundrum with gauge fields in the bulk, or some such. It would be (more) evidence for the AdS/CFT correspondence.

    There REALLY is no way to disprove string theory at the LHC, only constrain or PROVE it.
  4. Oct 28, 2007 #3


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    There is something going about the top quark, but I doubt it to be technicolour. GUT unifiers got attracted time ago for a so called "infrared fixed point conjecture" for the yukawa coupling of the top. On other hand, I am discussing in this other thread the process of beta decay, and it seems as if one could keep the fermi coupling while one restores isospin, and to do this you need other origin for the fermi coupling; the top quark can provide it.
  5. Oct 28, 2007 #4
    A more direct answer to your question---as far as ETC models go, I think you need large representations for the fermions---this gives you an approximately conformal symmetry above Lambda_TC (just like QCD at large energies), and allows you to generate the hierarchy with strong dynamics. They work with adjoint representations, for example. In heterotic string models, representations LARGER than the adjoint are pretty tough to get, and in general all of our reps are adjoint or smaller. The easy way to see this is that we have somehting like N=1 SUGRA in 10 dimensions, with the 248 (adjoint) of E8. If you consult Slansky, and try to find ways to break E8, you will always end up with representaitons that are adjoint or smaller.

    So if there were, say, an SU(3)_TC, AND there were fermions in some arbitrarily large representation, these models may bre difficult to get from weakly coupled heterotic strings.

    My previous comment, about the ETC models being the AdS duals to some RS1 model with gauge bosons in the bulk, still stands, though. And, as far as I know, RS1 has a good embedding into strings (Type IIA I think).

    As my previous comments might suggest, I disagree with this statement completely. SUSY is a way to generate the hierarchy, but low energy SUSY is by no means a prediction of string theory. If no evidence for SUSY is found, then a lot of the model building work (stringy AND non-stringy) will go out the window, and people will start building new models which reproduce the low energy data.
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