Editing Quantum field theory (section)

===Standard model===
[[File:Standard Model of Elementary Particles.svg|thumb|300px|[[Elementary particles]] of the [[Standard Model]]: six types of [[quark]]s, six types of [[lepton]]s, four types of [[gauge boson]]s that carry [[fundamental interaction]]s, as well as the [[Higgs boson]], which endow elementary particles with mass.]]
In 1954, [[Yang Chen-Ning]] and [[Robert Mills (physicist)|Robert Mills]] generalized the [[gauge theory|local symmetry]] of QED, leading to [[Yang–Mills theory|non-Abelian gauge theories]] (also known as Yang–Mills theories), which are based on more complicated local [[symmetry group]]s.<ref name="thooft">{{Cite book |last='t Hooft |first=Gerard |author-link=Gerard 't Hooft |arxiv=1503.05007 |chapter=The Evolution of Quantum Field Theory |title=The Standard Theory of Particle Physics |volume=26 |pages=1–27 |date=2015-03-17 |bibcode=2016stpp.conf....1T |doi=10.1142/9789814733519_0001 |series=Advanced Series on Directions in High Energy Physics |isbn=978-981-4733-50-2 |s2cid=119198452 }}</ref>{{rp|5}} In QED, (electrically) charged particles interact via the exchange of photons, while in non-Abelian gauge theory, particles carrying a new type of "[[charge (physics)|charge]]" interact via the exchange of massless [[gauge boson]]s. Unlike photons, these gauge bosons themselves carry charge.{{r|weinberg|page1=32}}<ref>{{cite journal |last1=Yang |first1=C. N. |last2=Mills |first2=R. L. |author-link1=Chen-Ning Yang |author-link2=Robert Mills (physicist) |date=1954-10-01 |title=Conservation of Isotopic Spin and Isotopic Gauge Invariance |journal=[[Physical Review]] |volume=96 |issue=1 |pages=191–195 |doi=10.1103/PhysRev.96.191 |bibcode=1954PhRv...96..191Y |doi-access=free }}</ref>

[[Sheldon Glashow]] developed a non-Abelian gauge theory that unified the electromagnetic and weak interactions in 1960. In 1964, [[Abdus Salam]] and [[John Clive Ward]] arrived at the same theory through a different path. This theory, nevertheless, was non-renormalizable.<ref name="coleman">{{cite journal |last=Coleman |first=Sidney |author-link=Sidney Coleman |date=1979-12-14 |title=The 1979 Nobel Prize in Physics |journal=[[Science (journal)|Science]] |volume=206 |issue=4424 |pages=1290–1292 |jstor=1749117 |bibcode=1979Sci...206.1290C |doi=10.1126/science.206.4424.1290 |pmid=17799637 }}</ref>

[[Peter Higgs]], [[Robert Brout]], [[François Englert]], [[Gerald Guralnik]], [[C. R. Hagen|Carl Hagen]], and [[T. W. B. Kibble|Tom Kibble]] proposed in their famous [[1964 PRL symmetry breaking papers|''Physical Review Letters'' papers]] that the gauge symmetry in Yang–Mills theories could be broken by a mechanism called [[spontaneous symmetry breaking]], through which originally massless gauge bosons could acquire mass.{{r|thooft|page1=5–6}}

By combining the earlier theory of Glashow, Salam, and Ward with the idea of spontaneous symmetry breaking, [[Steven Weinberg]] wrote down in 1967 a theory describing [[electroweak interaction]]s between all [[lepton]]s and the effects of the [[Higgs boson]]. His theory was at first mostly ignored,<ref name="coleman" />{{r|thooft|page1=6}} until it was brought back to light in 1971 by [[Gerard 't Hooft]]'s proof that non-Abelian gauge theories are renormalizable. The electroweak theory of Weinberg and Salam was extended from leptons to [[quark]]s in 1970 by Glashow, [[John Iliopoulos]], and [[Luciano Maiani]], marking its completion.<ref name="coleman" />

[[Harald Fritzsch]], [[Murray Gell-Mann]], and [[Heinrich Leutwyler]] discovered in 1971 that certain phenomena involving the [[strong interaction]] could also be explained by non-Abelian gauge theory. [[Quantum chromodynamics]] (QCD) was born. In 1973, [[David Gross]], [[Frank Wilczek]], and [[Hugh David Politzer]] showed that non-Abelian gauge theories are "[[asymptotic freedom|asymptotically free]]", meaning that under renormalization, the coupling constant of the strong interaction decreases as the interaction energy increases. (Similar discoveries had been made numerous times previously, but they had been largely ignored.) {{r|thooft|page1=11}} Therefore, at least in high-energy interactions, the coupling constant in QCD becomes sufficiently small to warrant a perturbative series expansion, making quantitative predictions for the strong interaction possible.{{r|weinberg|page1=32}}

These theoretical breakthroughs brought about a renaissance in QFT. The full theory, which includes the electroweak theory and chromodynamics, is referred to today as the [[Standard Model]] of elementary particles.<ref>{{cite web |url=https://www.britannica.com/science/Standard-Model |title=Standard model |last=Sutton |first=Christine |author-link=Christine Sutton |website=britannica.com |publisher=[[Encyclopædia Britannica]] |access-date=2018-08-14}}</ref> The Standard Model successfully describes all [[fundamental interaction]]s except [[gravity]], and its many predictions have been met with remarkable experimental confirmation in subsequent decades.{{r|shifman|page1=3}} The [[Higgs boson]], central to the mechanism of spontaneous symmetry breaking, was finally detected in 2012 at [[CERN]], marking the complete verification of the existence of all constituents of the Standard Model.<ref>{{cite arXiv |last=Kibble |first=Tom W. B. |author-link=Tom Kibble |eprint=1412.4094 |title=The Standard Model of Particle Physics |class=physics.hist-ph |date=2014-12-12 }}</ref>