Originally posted by AK-81
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Weak interaction is the mechanism for the weak force or weak nuclear force, one of the four fundamental forces of nature, alongside the strong interaction, electromagnetism, and gravitation. Weak interactions affect all known fermions; that is, particles whose spin (a property of all particles) is a half-integer. Weak interactions are responsible for the existence and structure of atomic nuclei, including the radioactive decay of subatomic particles and nuclear fusion.
In the Standard Model of particle physics the weak interaction is theorised as being caused by the exchange (i.e., emission or absorption) of W and Z bosons; and as such, is considered to be a non-contact force, like the other three forces. The best known effect of this emission is beta decay, a form of radioactivity. The W and Z bosons are much heavier than protons or neutrons and it is this heaviness that accounts for the very short range of the weak interaction. The force is termed weak because its typical field strength is several orders of magnitude less than that of both electromagnetism and the strong nuclear force. Most fermions will decay by a weak interaction over time. It has one unique property – namely quark flavour changing – that does not occur in any other interaction. In addition, it breaks parity-symmetry and CP-symmetry. Quark flavour changing allows for quarks to swap their 'flavour', one of six, for another.
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