How does a fermion, like an electron, get its mass through the Higgs-mechanism? Can someone explain me this with formulas (Lagrangian)?
I know that the Yukawa interaction has something to do with this, is that right?
Maybe when I'm right, there is a term:
gˉΨΦΨ?
Answer
It is about the "the 5-th force."
As you said the Yukawa term introducing the interaction between scalar field Φ and fermion Ψ field: gˉΨΦΨ
The Higgs mechanism causes the Φ field condense at a classical expectation value (v.e.v: vacuum expectation value), due to the Higgs potential U(Φ), so Φ tend to find a classical minimum, which causes:
Φ(x,t)→⟨Φ⟩=m
as a fix value m. You can imagine this process as originally Φ(x,t) is a field variable free to have any real/complex values at any spacetime (x,t) point due to quantum fluctuation. However, the Higgs mechanism causes ⟨Φ⟩=m finding a (local) classical stable minimum value of the potential U(Φ).
The remarkable result is that Φ(x,t) semi-classically now have to take the fix value at m at any spacetime point! (This is the remarkable fact of the 5-th force: Higgs field introduces mass to fermions i.e. quarks, leptons, in the Standard Model. Some people coin the name the 5-th force - a different mechanism from the 4 fundamental forces.)
Add: Some people like to think about (fermions,W±,Z0 bosons) particles moving in the ocean of Higgs fields, thus (fermion,W,Z) particles become massive due to the buoyancy force effects in the Higgs ocean.
The mass M of fermion fields now can be read as
gˉΨΦΨ→(g⋅m)ˉΨΨ=MˉΨΨ
Note that now Fermion mass takes the fixed value at g⟨Φ⟩, BUT there is quantum fluctuation around the v.e.v. (⟨Φ⟩+δΦ) to cause fermion field interacting with the Higgs fluctuation δΦ. You can draw a Feynman diagram to compute its effect.
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