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QCD vacuum contribution to W/Z masses

  1. Feb 12, 2012 #1
    The QCD vacuum condensate which breaks chiral symmetry in qcd, also break the SU(2) electoweak gauge symmtery, right?
    The operator which gets a vacuum expectation value isn't SU(2) invariant since it is built out of left handed quarks and right handed quarks which are in different representations of SU(2).
    This should contribute about ~100MeV the W and Z masses. Why is this never taken into account in EWPT? because the condensate should be the same for up and down type quarks, I would think it woudn't contibute to the T parameter (isospin symmetry), But it should contribute to the S parameter.
    Is this simply negligible, or I've got it all wrong?
  2. jcsd
  3. Feb 12, 2012 #2

    Vanadium 50

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    It is a real effect, although it's smaller than what you estimate: more like 10 or 20 MeV. It acts in quadrature with the Higgs mechanism, so the numeric effect on precision EWK is negligible.
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