Higgs Field – Which Particles Gain Mass?

higgsmassparticle-physicsstandard-modelsymmetry-breaking

I have found contradictory information about this. Does the Higgs field give mass only to the $W^+$, $W^-$, and $Z^0$ bosons or does it give mass to other particles as well?

Best Answer

The Higgs field $\phi$ undergoes spontaneous symmetry breaking$^\dagger$ (from a complex doublet to a real scalar field, whose quantum is the Higgs boson) in a process named the Higgs mechanism. $^\dagger$: well it's a local/gauge symmetry, not global, so it's not "real" SSB, hence the different name "Higgs mechanism".

This has two consequences:

  • the gauge bosons $W^\pm$ and $Z^0$ acquire a mass term, which they couldn’t have had a priori without breaking gauge invariance. The mass depends on the VEV (vacuum expectation value) of the Higgs field, but it doesn’t arise from a direct interaction term (see below) between the Higgs field and the gauge bosons. This new mass mode is the “would-be” Goldstone boson associated with the breaking of the Higgs field symmetry. (By “no direct interaction term” I mean that the term containing a product between the gauge boson and the Higgs field is hidden in the gauge covariant derivate $D^\mu$.)

  • the fundamental fermions (quarks, leptons, but not neutrinos) also acquire a mass term. This arises from a direct interaction term between the fermionic field $\psi$ and the Higgs field, called the Yukawa Lagrangian sector. This looks like $ \mathcal{L}_Y \propto \Gamma \bar L \phi R, $ where $\Gamma$ is the Yukawa coupling to the specific fermionic field $\psi$, and $L$ and $R$ are the left- and right- handed components of $\psi$. Neutrinos have no right-handed partner so they cannot gain mass through a Yukawa coupling.

So the Higgs field is responsible for the masses of all the elementary particles (including the Higgs boson) short of neutrinos.

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