- Fermi's interaction
In
physics , Fermi's interaction is an old explanation of theweak force , proposed byEnrico Fermi . Four fermions directly interact with one another. For example, this interaction is directly able to split aneutron (or two down-quark s and an up-quark) to anelectron ,antineutrino and aproton (or two up-quarks and a down-quark).Tree
Feynman diagram s describe the interaction remarkably well. Unfortunately, loop diagrams cannot be calculated reliably because Fermi's interaction is notrenormalizable . The solution is to replace the four-fermion contact interaction by a more complete theory (seeUV completion ) — an exchange of aW boson or aZ boson as explained in theelectroweak theory . The electroweak theory "is" renormalizable.Before the
electroweak theory and theStandard Model were constructed,George Sudarshan andRobert Marshak , and also independentlyRichard Feynman andMurray Gell-Mann were able to determine the correct tensor structure (vector minusaxial vector , V−A) of the four-fermion interaction.Fermi constant
The strength of Fermi's interaction is given by the Fermi constant . In modern terms,
Here is the
coupling constant of theweak interaction , and is the mass of theW boson .
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