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You have no way to know if the virtual particle is a gamma or a Z. Actually, it does not really make sense, since no measurement can tell you what has been exchanged. You always have to envisage all the possibilities resulting from the perturbative series used to describe the theory. It's a bit as asking in the double slits young experiment, which slit has ...

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What I have retained from lectures on symmetry breaking is that when trying to write a unified Lagrangian for weak and electromagnetic interactions, one is faced with the fact that the electromagnetic interaction has infinite range and thus can exchange a zero mass particle, the photon, the weak, because it experimentally has a small range , must have ...

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I am going to take a stab at answering my own questions with what I have been able to find on the subject. (Still very sparse.) 1) In this model the SU(2) confinement occurs at much higher energies than SU(3) confinement, so that the weak-partons confine first (giving us quarks and leptons) and then quarks confine into hadrons second. This explains why ...

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When energy in a given reaction is much larger than the masses of all leptons, these masses can be neglected. For example if you consider $W$ bosons decays, then $$M_W \gg m_\tau.$$ Tau is the heaviest among the charged leptons, so if you can neglect mass of the tau, you also can neglect masses of other leptons. But now you neglected the only quantity that ...

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As your QFT theory text should tell you, for an action invariant under G, addition of a Higgs potential only invariant under its subgroup H will spontaneously break the generators in G/H. You ought to do due diligence and study and understand and reproduce all examples of elementary classics such as Ling-Fong Li, PhysRev D9 (1974) 1723. There are, of ...

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