weakinteraction

The weak interaction is one of the four fundamental forces of nature. It governs processes that change the flavor of quarks and leptons and is responsible for phenomena such as beta decay. Compared with the other forces, it acts at very short ranges and is significant mainly inside atomic nuclei for certain transitions.

The weak interaction is carried by gauge bosons W± and Z0. Charged-current interactions, mediated by W±, change electric charge and flavor (for example in beta decay); neutral-current interactions, mediated by Z0, transfer momentum without changing charge. The interaction exhibits a V-A structure, which leads to parity violation in weak processes.

The force is short-ranged because the W and Z bosons are massive (about 80 and 91 GeV). The effective coupling at low energies is described by the Fermi constant G_F. At high energies the electroweak theory unifies the weak and electromagnetic interactions, with W and Z masses arising from spontaneous symmetry breaking via the Higgs mechanism.

Flavor mixing is encoded in the CKM matrix for quarks and the PMNS matrix for leptons; weak interactions also exhibit CP violation in certain decays. Neutrino oscillations imply nonzero neutrino masses, requiring physics beyond the simplest Standard Model.

In nature, the weak force drives beta decay, muon decay, and neutrino scattering, and it enables energy production in stars through fusion processes that produce neutrinos. The theory originated with Fermi’s theory in the 1930s and was confirmed by the discovery of the W and Z bosons in 1983.

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