In particle physics, the weak interaction is the mechanism responsible for the weak force or weak nuclear force, one of the four fundamental interactions of nature, alongside the strong interaction, electromagnetism, and gravitation. The theory of the weak interaction is sometimes called quantum flavordynamics (QFD), in analogy with the terms QCD and QED, but in practice the term is rarely used because the weak force is best understood in terms of electro-weak theory
In the Standard Model of particle physics the weak interaction is caused by the emission or absorption of W and Z bosons. All known fermions interact through the weak interaction. Fermions are particles one of whose properties, spin, is a half-integer. A fermion can be an elementary particle, such as the electron; or it can be a composite particle, such as the proton. W and Z bosons are much heavier than protons or neutrons and this heaviness means that the weak force has a very short range. The force is termed weak because its field strength over a given distance is typically several orders of magnitude less than that of the strong nuclear force and electromagnetism.
The weak interaction is responsible for the existence and structure of atomic nuclei, and is responsible for both the radioactive decay and nuclear fusion of subatomic particles. Most fermions will decay by a weak interaction over time. Important examples include beta decay, and the production of deuterium and then helium from hydrogen that powers the sun's thermonuclear process. Such decay also makes radiocarbon dating possible, as carbon-14 decays through the weak interaction to nitrogen-14. It can also create radioluminescence, commonly used in tritium illumination, and in the related field of betavoltaics.
