What is "weak interaction"

n. (context physics English) The fundamental interaction responsible for the weak nuclear force.

n. (physics) an interaction between elementary particles involving neutrinos or antineutrinos that is responsible for certain kinds of radioactive decay; mediated by intermediate vector bosons [syn: weak force]

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 flavordynamics (QFD), in analogy with the terms QCD and QED, but the term is rarely used because the weak force is best understood in terms of electro-weak theory (EWT).

In the Standard Model of particle physics, the weak interaction is caused by the emission or absorption of the force carriers, the W and Z bosons. All known fermions interact through the weak interaction. Fermions are particles that have half-integer spin. Spin is one of the fundamental properties of particles. A fermion can be an elementary particle, such as the electron, or it can be a composite particle, such as the proton. The masses of W, W, and Z bosons are each far greater than that of interacting protons or neutrons, which is consistent with the short range of the weak force. 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 electromagnetic force.

During the quark epoch of the early universe, the electroweak force separated into the electromagnetic and weak forces. Important examples of the weak interaction include beta decay, and the fusion of hydrogen into deuterium that powers the Sun's thermonuclear process. Most fermions will decay by a weak interaction over time. Such decay 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.

Quarks, which make up composite particles like neutrons and protons, come in six "flavours" – up, down, strange, charm, top and bottom – which give those composite particles their properties. The weak interaction is unique in that it allows for quarks to swap their flavour for another. The swapping of those properties is mediated by the force carrier bosons. For example, during beta minus decay, a down quark within a neutron is changed into an up quark, converting the neutron to a proton and resulting in the emission of an electron and an electron antineutrino. Also, the weak interaction is the only fundamental interaction that breaks parity-symmetry, and similarly, the only one to break charge parity symmetry.