Weak nuclear interactions
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Weak nuclear interactions
Fundamental interactions of nature that play a significant role in elementary particle and nuclear physics, and are distinguished from other such interactions by special properties such as participation of all the fundamental fermions and failure to conserve parity. The weak force has very short range (less than 10-17m) and is extremely feeble compared to strong and electromagnetic forces, but can be distinguished from these two by its special character. For example, according to the present view, all of matter consists of certain fundamental spin-½ constituents, the quarks and leptons, collectively called the fundamental fermions. While only the quarks participate in strong interactions, and only the quarks and charged leptons e, μ, and τ participate in electromagnetic interactions, all of the fundamental fermions, including neutrinos, engage in weak interactions. Also, the strong and electromagnetic interactions respect spatial inversion symmetry (they conserve parity) and are also particle-antiparticle (charge conjugation) symmetric, whereas the weak interaction violates these two symmetries. See Fundamental interactions, Lepton, Parity (quantum mechanics), Quarks, Symmetry laws (physics)
Weak interactions are classified as “charged” or “neutral,” depending on whether or not a particle participating in a weak reaction suffers a change of electric charge of one electronic unit. Observed charged weak interactions include nuclear beta decay and electron capture, muon capture on nuclei, and the slow decays of unstable elementary particles such as the μ and τ leptons, π, K, and charmed mesons, and hyperons and charmed baryons. Also, there are the charged neutrino-nucleon and neutrino-lepton scattering reactions. Neutral weak interactions include neutrino-nucleon and neutrino-lepton scattering as well as the electron-nucleon reaction which can also occur by electromagnetic interaction. See Baryon, Elementary particle, Hyperon, Meson
The most important development in the study of weak interactions has been the creation of a successful theory based on the principles of local gauge invariance and spontaneous symmetry breaking. This theory proposes a single basis for the weak and electromagnetic interactions, and indeed, despite striking differences in the observed characteristics of strong, electromagnetic, and weak interactions, important theoretical ideas of a similar type suggest that all these interactions possess a common origin.