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There ate two types of vacuum of the Standard model-the vacuum of the Higgs potential and that of the vacuum of the Yang-Mills fields labelled by the Chern-Simons number. See the figure 5 here.

The Lagrangian of the Standard electroweak theory contains both the gauge fields and Higgs doublet. Through the gauge covariant derivative the Higgs doublet couples to the gauge fields. So are they really different theories? As I understand, after the electroweak symmetry breaking the Universe is locked at one point/direction of the vacuum manifold of the Higgs potential. But I also hear about the Universe being in one of the vacua labelled by the Chern-Simons number.

My question is which vacuum is the Universe really in?

SRS
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1 Answers1

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A "pure" Higgs theory (i.e. containing only the Higgs field) has a vacuum labeled by the VEV of the Higgs field, a pure YM theory has a vacuum labeled by the $\theta$-angle, and the combined theory, i.e. a YM theory with a Higgs field as we find it in the standard model, has a vacuum labeled by both the Higgs VEV and the $\theta$-angle.

ACuriousMind
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