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Fermi first introduced this coupling in his description of beta decay in 1933. [3] The Fermi interaction was the precursor to the theory for the weak interaction where the interaction between the proton–neutron and electron–antineutrino is mediated by a virtual W − boson, of which the Fermi theory is the low-energy effective field theory.
The weak interaction has a very short effective range (around 10 −17 to 10 −16 m (0.01 to 0.1 fm)). [b] [14] [13] At distances around 10 −18 meters (0.001 fm), the weak interaction has an intensity of a similar magnitude to the electromagnetic force, but this starts to decrease exponentially with increasing distance.
Fermi's theory of the weak interaction. The interaction term has a V − A (vector minus axial) form. The Gross–Neveu model. This is a four-fermi theory of Dirac fermions without chiral symmetry and as such, it may or may not be massive. The Thirring model. This is a four-fermi theory of fermions with a vector coupling. The Nambu–Jona ...
Fermi's interaction showing the 4-point fermion vector current, coupled under the Fermi coupling constant, G F. Fermi's theory was the first theoretical effort in describing nuclear decay rates for beta decay. The Gamow–Teller theory was a necessary extension of Fermi's theory.
This table gives the values of the electric charge (the coupling to the photon, referred to in this article as [a]). Also listed are the approximate weak charge (the vector part of the Z boson coupling to fermions), weak isospin (the coupling to the W bosons), weak hypercharge (the coupling to the B boson) and the approximate Z boson coupling factors (and in the "Theoretical" section, below).
In the case of the weak interaction, which can in principle engage with both left- and right-chiral fermions, only two left-handed fermions interact. Interactions involving right-handed or opposite-handed fermions have not been shown to occur, implying that the universe has a preference for left-handed chirality.
In particular, under weak isospin SU(2) transformations the left-handed particles are weak-isospin doublets, whereas the right-handed are singlets – i.e. the weak isospin of ψ R is zero. Put more simply, the weak interaction could rotate e.g. a left-handed electron into a left-handed neutrino (with emission of a W − ), but could not do so ...
The coupling with the Higgs field for fermions gives an interaction term = ¯, with being the Dirac field and the Higgs field. Also, the mass of a fermion is proportional to its Yukawa coupling, meaning that the Higgs boson will couple most to the most massive particle.