7.3 Weak Force

This manifests itself through nuclear $\beta$ decay,

$$n\to p+e^{-}+\overline{{\nu }_e}.$$

(7.7)

The standard coupling for this theory is called the Fermi coupling, $G_F$, after its discoverer. After the theory was introduced it was discovered that there were physical particles that mediate the weak force, the $W^{\pm }$ and the $Z^0$ bosons. These are very heavy particles (their mass is about 80 times the proton mass!), which is why they have such a small range – fluctuations where I need to create that much mass are rare. The $W^{\pm }$ bosons are charged, and the $Z^0$ boson is neutral. The typical $\beta$ decay referred to above is mediated by a $W^{-}$ boson as can be seen in the Feynman diagram figure 7.1 . The reason for this choice is that it conserves charge at each point (the charge of a proton and a $W^{-}$ is zero, the charge of an electron and a neutrino is -1, the same as that of a $W^{-}$).

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