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I read that above unification energy, on the order of 100 GeV, electromagnetic force and weak force would merge into a single electroweak force. I do not really understand how and when exactly two forces are getting unified in terms of the mass scale that is given.

Going through Glashow-Weinberg-Salam's Electroweak model, I understood how the SSB $SU(2)_L\times U(1)_Y\rightarrow U(1)_{EM}$ gives rise to masses of $W^{\pm}, Z$ bosons ($\sim 100$ GeV), but I do not understand when exactly the theory is getting unified (or what exactly does it mean).

Things that confuse me are when exactly the forces appear to be unified and when they get broken (in terms of energy scales).

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The link you are referencing indicates that the operative scale is $v= 246$GeV, not 100; but if that's what you have in mind, the loose language "unified" indicates that, for ambient (thermal) energies above that v, the massive weak bosons W and Z mix with the photon mediating electromagnetism into the ๐‘†๐‘ˆ(2)๐ฟร—๐‘ˆ(1)๐‘Œ theory.

This weak mixing/blending is metaphorically dubbed "unification", in the loose sense it represents inseparable aspects of the same structure, loosely as electric and magnetic forces blend into Maxwell's "unified" electromagnetism. It is a popular language thing.

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  • $\begingroup$ I think it is useful to note that the electroweak theory carries 4 separate bosons, the 3 electroweak bosons and the hypercharge boson, just like you have 4 different bosons (weak + EM) in the broken phase. As you already stated, a more useful term is probably "mixing" rather then "unifying" $\endgroup$
    – LolloBoldo
    Sep 6, 2023 at 21:56

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