Weak interaction

In particle physics, the weak interaction (the weak force or weak nuclear force) is one of the four known fundamental interactions of nature, alongside the strong interaction, electromagnetism, and gravitation. The weak interaction is responsible for radioactive decay, which plays an essential role in nuclear fission. The theory of the weak interaction is sometimes called quantum flavourdynamics (QFD), in analogy with the terms QCD dealing with the strong interaction and QED dealing with the electromagnetic force. However the term QFD is rarely used because the weak force is best understood in terms of electro-weak theory (EWT).

The Standard Model of particle physics, which does not address gravity, provides a uniform framework for understanding how the electromagnetic, weak, and strong interactions work. An interaction occurs when two particles, typically but not necessarily half-integer spin fermions, exchange integer-spin, force-carrying bosons. The fermions involved in such exchanges can be either elementary (e.g. electrons or quarks) or composite (e.g. protons or neutrons), although at the deepest levels, all weak interactions ultimately are between elementary particles. In the case of the weak interaction, fermions can exchange three distinct types of force carriers known as the W⁺, W⁻, and Z bosons. The mass of each of these bosons is far greater than the mass of a proton or neutron, which is consistent with the short range of the weak force. The force is in fact termed weak because its field strength over a given distance is typically several orders of magnitude less than that of the strong nuclear force or electromagnetic force.

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