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| | I'm Stephan and I live in a seaside city in northern United States, Independence. I'm 33 and I'm will soon finish my study at Biochemistry.<br><br>Stop by my blog post - [http://generalwellbeing.com/node/178595 how to get free fifa 15 coins] |
| {{Standard model of particle physics}}
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| In [[particle physics]], the '''weak interaction''' is the mechanism responsible for the '''weak force''' or '''weak nuclear force''', one of the four [[fundamental interaction]]s of nature, alongside the [[strong interaction]], [[electromagnetism]], and [[gravitation]]. The weak interaction is responsible for both the [[radioactive decay]] and [[nuclear fusion]] of [[subatomic particles]]. The theory of the weak interaction is sometimes called '''quantum flavordynamics''' (QFD), in analogy with the terms [[Quantum chromodynamics|QCD]] and [[Quantum electrodynamics|QED]], but in practice the term is rarely used because the weak force is best understood in terms of [[Electroweak interaction|electro-weak theory]] (EWT).<ref name="griffiths">{{cite book|last=Griffiths|first=David|title=Introduction to Elementary Particles |year=2009|isbn=978-3-527-40601-2|pages=59–60}}</ref>
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| In the [[Standard Model]] of [[particle physics]] the weak interaction is caused by the emission or absorption of [[W and Z bosons]]. All known [[fermion]]s interact through the weak interaction. Fermions are particles, one of whose properties, [[spin (physics)|spin]], is a [[half-integer]]. A fermion can be an [[elementary particle]], such as the [[electron]]; or it can be a [[composite particle]], such as the [[proton]]. The heavy mass of W± and Z bosons being far heavier than protons or neutrons creates the short-range in the weak force. However, the weak force generally operates over a longer distance than the strong force. The force is termed ''weak'' because its field strength over a given distance is typically several orders of magnitude less than<sup>[misleading?]</sup> that of the [[strong nuclear force]] and [[electromagnetism]].
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| During the [[quark epoch]], the electroweak force split into the electromagnetic and [[weak force]]. Most fermions will decay by a weak interaction over time. Important examples include [[beta decay]], and the production of deuterium and then helium from hydrogen that powers the sun's thermonuclear process. Such decay also 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]].<ref>{{cite web |url=http://nobelprize.org/nobel_prizes/physics/laureates/1979/press.html |title=The Nobel Prize in Physics 1979: Press Release |work=NobelPrize.org |publisher=Nobel Media |accessdate=22 March 2011}}</ref>
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| [[Quark]]s, 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. For example, during beta minus decay, a down quark decays into an up quark, converting a neutron to a proton. In addition, the weak interaction is the only fundamental interaction that breaks [[Parity (physics)|parity-symmetry]], and similarly, the only one to break [[CP-symmetry]].
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| ==History==
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| In 1933, Enrico Fermi proposed the first theory of the weak interaction, known as [[Fermi's interaction]]. He suggested that [[beta decay]] could be explained by a four-[[fermion]] interaction, involving a contact force with no range.<ref name="Fermi's theory">{{cite journal | title=Versuch einer Theorie der β-Strahlen. I | author=Fermi, Enrico | bibcode=1934ZPhy...88..161F | journal=[[Zeitschrift für Physik A]] | year=1934 | volume=88 | issue=3–4 | pages=161–177 | doi=10.1007/BF01351864}}</ref><ref name="Fermi's theory translation">{{cite journal | title=Fermi's Theory of Beta Decay | author=Wilson, Fred L. | journal=American Journal of Physics |date=December 1968 | volume=36 | issue=12 | pages=1150-1160 | doi=10.1119/1.1974382}}</ref>
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| However it is better described as a [[non-contact force]] field having a finite range, albeit very short. In 1968 [[Sheldon Glashow]], [[Abdus Salam]] and [[Steven Weinberg]] unified the electromagnetic force and the weak interaction by showing them to be two aspects of a single force, now termed the electro-weak force.
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| The [[W and Z bosons#Discovery|existence of the W and Z bosons]] was not directly confirmed until 1983.
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| ==Properties==
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| [[File:Weak Decay (flipped).svg|thumb|right|280px|A diagram depicting the various decay routes due to the weak interaction and some indication of their likelihood. The intensity of the lines are given by the [[CKM parameters]].]]
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| The weak interaction is unique in a number of respects:
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| # It is the only interaction capable of changing the [[flavor (particle physics)|flavor]] of quarks (i.e., of changing one type of quark into another).
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| # It is the only interaction which violates [[parity (physics)|'''P''' or parity-symmetry]]. It is also the only one which violates [[CP-symmetry|'''CP''' symmetry]].
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| # It is propagated by carrier particles (known as [[gauge boson]]s) that have significant masses, an unusual feature which is explained in the [[Standard Model]] by the [[Higgs mechanism]].
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| Due to their large mass (approximately 90 GeV/c<sup>2</sup><ref name="PDG">{{cite journal |author=W.-M. Yao ''et al''. ([[Particle Data Group]]) |year=2006 |title=Review of Particle Physics: Quarks |url=http://pdg.lbl.gov/2006/tables/qxxx.pdf |journal=[[Journal of Physics G]] |volume=33 |page=1 |doi=10.1088/0954-3899/33/1/001 |arxiv = astro-ph/0601168 |bibcode = 2006JPhG...33....1Y }}</ref>) these carrier particles, termed the W and Z bosons, are short-lived: they have a [[mean life|lifetime]] of under 1×10<sup>−24</sup> seconds.<ref>{{cite book |title=Story of the W and Z |author=Peter Watkins |publisher=[[Cambridge University Press]] |location=Cambridge |url=http://books.google.co.uk/books?id=J808AAAAIAAJ&pg=PA70 |page=70 |year=1986 |isbn=978-0-521-31875-4}}</ref> The weak interaction has a [[coupling constant]] (an indicator of interaction strength) of between 10<sup>−7</sup> and 10<sup>−6</sup>, compared to the strong interaction's coupling constant of about 1 and the [[Fine Structure Constant|electromagnetic coupling constant]] of about 10<sup>−2</sup>;<ref name="coupling">{{cite web |url=http://hyperphysics.phy-astr.gsu.edu/hbase/forces/couple.html |title=Coupling Constants for the Fundamental Forces |work=HyperPhysics | publisher =Georgia State University |accessdate=2 March 2011}}</ref> consequently the weak interaction is weak in terms of strength.<ref name="physnet"/> The weak interaction has a very short range (around 10<sup>−17</sup>–10<sup>−16</sup> m<ref name="physnet">{{cite web |url=http://physnet2.pa.msu.edu/home/modules/pdf_modules/m281.pdf |title=The Weak Interaction |author=J. Christman |publisher=Michigan State University |work=Physnet |year=2001}}</ref>).<ref name="coupling"/> At distances around 10<sup>−18</sup> meters, the weak interaction has a strength of a similar magnitude to the electromagnetic force; but at distances of around 3×10<sup>−17</sup> m the weak interaction is 10,000 times weaker than the electromagnetic.<ref>{{cite web |url=http://www.particleadventure.org/electroweak.html |title=Electroweak |work=The Particle Adventure |publisher=[[Particle Data Group]] |accessdate=3 March 2011}}</ref>
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| The weak interaction affects all the [[fermions]] of the [[Standard Model]], as well as the [[Higgs boson]]; [[neutrino]]s interact through gravity and the weak interaction only, and neutrinos were the original reason for the name ''weak force''.<ref name="physnet"/> The weak interaction does not produce [[bound states]] (nor does it involve [[binding energy]]) – something that gravity does on an astronomical scale, that the electromagnetic force does at the atomic level, and that the strong nuclear force does inside nuclei.<ref name="greiner">{{cite book |url=http://books.google.co.uk/books?id=yWTcPwqg_00C |title=Gauge Theory of Weak Interactions |author1=Walter Greiner |author2=Berndt Müller |publisher=Springer |page=2 |year=2009 |isbn=978-3-540-87842-1}}</ref>
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| Its most noticeable effect is due to its first unique feature: [[Flavour changing processes|flavor changing]]. A [[neutron]], for example, is heavier than a [[proton]] (its sister [[nucleon]]), but it cannot decay into a proton without changing the [[flavour (particle physics)|flavor]] (type) of one of its two ''down'' quarks to ''up''. Neither the [[strong interaction]] nor [[electromagnetism]] permit flavour changing, so this must proceed by '''weak decay'''; without weak decay, quark properties such as strangeness and charm (associated with the quarks of the same name) would also be conserved across all interactions. All [[mesons]] are unstable because of weak decay.<ref>Cottingham & Greenwood (1986, 2001), p.29</ref> In the process known as [[beta decay]], a ''down'' quark in the [[neutron]] can change into an ''up'' quark by emitting a [[Virtual particle|virtual]] {{SubatomicParticle|W boson-}} boson which is then converted into an [[electron]] and an electron [[antineutrino]].<ref name="Cott28"/>
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| Due to the large mass of a [[boson]], weak decay is much more unlikely than strong or electromagnetic decay, and hence occurs less rapidly. For example, a neutral [[pion]] (which decays electromagnetically) has a life of about 10<sup>−16</sup> seconds, while a charged pion (which decays through the weak interaction) lives about 10<sup>−8</sup> seconds, a hundred million times longer.<ref name="Cottingham30">Cottingham & Greenwood (1986, 2001), p.30</ref> In contrast, a free neutron (which also decays through the weak interaction) lives about 15 minutes.<ref name="Cott28">Cottingham & Greenwood (1986, 2001), p.28</ref>
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| ===Weak isospin and weak hypercharge===
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| {{main|Weak isospin}}
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| {| style="float:right; margin:0 0 .5em 1em;" class="wikitable"
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| |+'''Left-handed fermions in the Standard Model'''.<ref name="baez">{{Cite journal |first1=John C. |last1=Baez |authorlink1=John C. Baez |first2=John |last2=Huerta |year=2009 |title=The Algebra of Grand Unified Theories|url=http://math.ucr.edu/~huerta/guts/node9.html |bibcode=2009arXiv0904.1556B |volume=0904 |pages=483–552 |arxiv=0904.1556 |journal=Bull.Am.Math.Soc. |deadurl=no |accessdate=15 October 2013}}</ref>
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| |-
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| !colspan="3" style="background:#ffdead"|Generation 1
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| !colspan="3" style="background:#ffdead"|Generation 2
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| !colspan="3" style="background:#ffdead"|Generation 3
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| |- style="background:#fdd;"
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| !Fermion
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| !Symbol
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| ![[Weak isospin|Weak<br />isospin]]
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| !Fermion
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| !Symbol
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| ![[Weak isospin|Weak<br />isospin]]
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| !Fermion
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| !Symbol
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| ![[Weak isospin|Weak<br />isospin]]
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| |-
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| |style="background:#efefef"|[[Electron]]
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| |<math>e^-\,</math>
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| |<math>-1/2\,</math>
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| |style="background:#efefef"|[[Muon]]
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| |<math>\mu^-\,</math>
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| |<math>-1/2\,</math>
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| |style="background:#efefef"|[[Tau (particle)|Tau]]
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| |<math>\tau^-\,</math>
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| |<math>-1/2\,</math>
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| |-
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| |style="background:#efefef"|[[Electron neutrino]]
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| |<math>\nu_e\,</math>
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| |<math>+1/2\,</math>
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| |style="background:#efefef"|[[Muon neutrino]]
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| |<math>\nu_\mu\,</math>
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| |<math>+1/2\,</math>
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| |style="background:#efefef"|[[Tau neutrino]]
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| |<math>\nu_\tau\,</math>
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| |<math>+1/2\,</math>
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| |-
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| |style="background:#efefef"|[[Up quark]]
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| |<math>u\,</math>
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| |<math>+1/2\,</math>
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| |style="background:#efefef"|[[Charm quark]]
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| |<math>c\,</math>
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| |<math>+1/2\,</math>
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| |style="background:#efefef"|[[Top quark]]
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| |<math>t\,</math>
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| |<math>+1/2\,</math>
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| |-
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| |style="background:#efefef"|[[Down quark]]
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| |<math>d\,</math>
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| |<math>-1/2\,</math>
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| |style="background:#efefef"|[[Strange quark]]
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| |<math>s\,</math>
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| |<math>-1/2\,</math>
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| |style="background:#efefef"|[[Bottom quark]]
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| |<math>b\,</math>
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| |<math>-1/2\,</math>
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| |-
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| | colspan="9" style="text-align:center;"|All left-handed antiparticles have weak isospin of 0.<br>Right-handed antiparticles have the opposite weak isospin.
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| |}
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| All particles have a property called weak isospin (T<sub>3</sub>) which serves as a [[quantum number]] and governs how that particle interacts in the weak interaction. Weak isospin therefore plays the same role in the weak interaction as [[electric charge]] in [[electromagnetism]], and [[color charge]] in the [[strong interaction]]. All [[fermion]]s have a weak isospin value of either +{{frac|2}} or −{{frac|2}}. For example, the up quark has a T<sub>3</sub> of +{{frac|2}} and the down quark −{{frac|2}}. A quark never decays through the weak interaction into a quark of the same T<sub>3</sub>: quarks with a T<sub>3</sub> of +{{frac|2}} decay into quarks with a T<sub>3</sub> of −{{frac|2}} and vice versa.
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| [[File:PiPlus-muon-decay.png|thumb|left|{{SubatomicParticle|Pion+}} decay through the weak interaction]]
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| In any given interaction, weak isospin is [[conservation law|conserved]]: the sum of the weak isospin numbers of the particles entering the interaction equals the sum of the weak isospin numbers of the particles exiting that interaction. For example, a (left-handed) {{SubatomicParticle|Pion+}}, with a weak isospin of 1 normally decays into a {{SubatomicParticle|Muon neutrino}} (+1/2) and a {{SubatomicParticle|Muon+}} (as a right-handed antiparticle, +1/2).<ref name="Cottingham30"/>
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| Following the development of the electroweak theory, another property, [[weak hypercharge]], was developed. It is dependent on a particle's electrical charge and weak isospin, and is defined as:
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| :<math>\qquad Y_W = 2(Q - T_3)</math>
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| where ''Y<sub>W</sub>'' is the weak hypercharge of a given type of particle, ''Q'' is its electrical charge (in [[elementary charge]] units) and ''T<sub>3</sub>'' is its weak isospin. Whereas some particles have a weak isospin of zero, all particles, except gluons, have non-zero weak hypercharge.{{Citation needed|date=April 2011}} Weak hypercharge is the generator of the U(1) component of the electroweak [[gauge group]].{{Citation needed|date=April 2011}}
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| ==Interaction types==
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| There are two types of weak interaction (called ''[[Feynman diagram|vertices]]''). The first type is called the "[[charged-current interaction]]" because it is [[force carrier|mediated]] by particles that carry an [[electric charge]] (the [[W boson|{{SubatomicParticle|W boson+}} or {{SubatomicParticle|W boson-}} bosons]]), and is responsible for the [[beta decay]] phenomenon. The second type is called the "[[neutral-current interaction]]" because it is mediated by a neutral particle, the [[Z boson]].
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| ===Charged-current interaction===
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| [[File:Beta Negative Decay.svg|thumb|right|200px|The [[Feynman diagram]] for beta-minus decay of a [[neutron]] into a [[proton]], [[electron]] and [[neutrino|electron anti-neutrino]], via an intermediate heavy {{SubatomicParticle|W boson-}} boson ]]
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| In one type of charged current interaction, a charged [[lepton]] (such as an [[electron]] or a [[muon]], having a charge of −1) can absorb a [[W boson|{{SubatomicParticle|W boson+}} boson]] (a particle with a charge of +1) and be thereby converted into a corresponding [[neutrino]] (with a charge of 0), where the type ("family") of neutrino (electron, muon or tau) is the same as the type of lepton in the interaction, for example:
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| :<math>\mu^-+ W^+\to \nu_\mu</math>
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| Similarly, a down-type [[quark]] (''d'' with a charge of −{{frac|3}}) can be converted into an up-type quark (''u'', with a charge of +{{frac|2|3}}), by emitting a {{SubatomicParticle|W boson-}} boson or by absorbing a {{SubatomicParticle|W boson+}} boson. More precisely, the down-type quark becomes a [[quantum superposition]] of up-type quarks: that is to say, it has a possibility of becoming any one of the three up-type quarks, with the probabilities given in the [[CKM matrix]] tables. Conversely, an up-type quark can emit a {{SubatomicParticle|W boson+}} boson – or absorb a {{SubatomicParticle|W boson-}} boson – and thereby be converted into a down-type quark, for example:
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| :<math>d \to u+ W^-</math>
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| :<math>d+ W^+\to u </math>
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| :<math>c\to s + W^+</math>
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| :<math>c+ W^-\to s</math>
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| The W boson is unstable so will rapidly decay, with a very short lifetime. For example:
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| :<math>W^-\to e^- + \bar\nu_e~</math>
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| :<math>W^+\to e^+ + \nu_e~</math>
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| Decay of the W boson to other products can happen, with varying probabilities.<ref name="PDG2">{{cite journal |author=K. Nakamura ''et al''. ([[Particle Data Group]]) |year=2010 |title=Gauge and Higgs Bosons |url=http://pdg.lbl.gov/2010/tables/rpp2010-sum-gauge-higgs-bosons.pdf |journal=[[Journal of Physics G]] |volume=37}}</ref>
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| In the so-called [[beta decay]] of a neutron (see picture, above), a down quark within the neutron emits a [[Virtual particle|virtual]] {{SubatomicParticle|W boson-}} boson and is thereby converted into an up quark, converting the neutron into a proton. Because of the energy involved in the process (i.e., the mass difference between the down quark and the up quark), the {{SubatomicParticle|W boson-}} boson can only be converted into an electron and an electron-antineutrino.<ref name="PDG3">{{cite journal |author=K. Nakamura ''et al''. ([[Particle Data Group]]) |year=2010 |title= n |url=http://pdg.lbl.gov/2010/listings/rpp2010-list-n.pdf |journal=[[Journal of Physics G]] |volume=37 |page=7}}</ref> At the quark level, the process can be represented as:
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| :<math>d\to u+ e^- + \bar\nu_e~</math>
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| ===Neutral-current interaction===
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| In [[neutral current]] interactions, a quark or a lepton (e.g., an [[electron]] or a [[muon]]) emits or absorbs a neutral [[Z boson]]. For example:
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| :<math>e^-\to e^- + Z^0</math>
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| Like the W boson, the Z boson also decays rapidly,<ref name="PDG2"/> for example:
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| :<math>Z^0\to b+\bar b</math>
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| ==Electroweak theory==
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| {{main|Electroweak interaction}}
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| The [[Standard Model]] of particle physics describes the [[electromagnetic interaction]] and the weak interaction as two different aspects of a single electroweak interaction, the theory of which was developed around 1968 by [[Sheldon Glashow]], [[Abdus Salam]] and [[Steven Weinberg]]. They were awarded the [[Nobel Prize in Physics#1970s|1979 Nobel Prize in Physics]] for their work.<ref>{{cite web |publisher=Nobel Media |work=NobelPrize.org |title=The Nobel Prize in Physics 1979 |url=http://nobelprize.org/nobel_prizes/physics/laureates/1979/ |accessdate=26 February 2011}}</ref> The [[Higgs mechanism]] provides an explanation for the presence of three massive gauge bosons (the three carriers of the weak interaction) and the massless photon of the electromagnetic interaction.<ref name="PDGHiggs">{{cite journal
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| |author=C. Amsler ''et al.'' ([[Particle Data Group]])
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| |year=2008
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| |title=Review of Particle Physics – Higgs Bosons: Theory and Searches
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| |url=http://pdg.lbl.gov/2008/reviews/higgs_s055.pdf
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| |journal=[[Physics Letters B]]
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| |volume=667 |issue= |page=1
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| |doi= 10.1016/j.physletb.2008.07.018
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| |bibcode = 2008PhLB..667....1P }}</ref>
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| According to the electroweak theory, at very high energies, the universe has four massless gauge boson fields similar to the [[photon]] and a complex scalar [[Higgs field]] doublet. However, at low energies, gauge symmetry is [[spontaneous symmetry breaking|spontaneously broken]] down to the '''U'''(1) symmetry of electromagnetism (one of the Higgs fields acquires a [[vacuum expectation value]]). This symmetry breaking would produce three massless [[Goldstone boson|boson]]s, but they become integrated by three photon-like fields (through the [[Higgs mechanism]]) giving them mass. These three fields become the {{SubatomicParticle|W boson+}}, {{SubatomicParticle|W boson-}} and Z bosons of the weak interaction, while the fourth gauge field which remains massless is the photon of electromagnetism.<ref name="PDGHiggs"/>
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| This theory has made a number of predictions, including a prediction of the masses of the Z and W bosons before their discovery. On 4 July 2012, the CMS and the ATLAS experimental teams at the [[Large Hadron Collider]] independently announced that they each confirmed the formal discovery of a previously unknown boson of mass between 125–127 GeV/''c''<sup>2</sup>, whose behaviour so far was "consistent with" a Higgs boson, while adding a cautious note that further data and analysis were needed before positively identifying the new boson as being a Higgs boson of some type. By 14 March 2013, the Higgs boson was tentatively confirmed to exist .<ref>{{cite web|url=http://home.web.cern.ch/about/updates/2013/03/new-results-indicate-new-particle-higgs-boson |title=New results indicate that new particle is a Higgs boson | CERN |publisher=Home.web.cern.ch |date= |accessdate=20 September 2013}}</ref>
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| ==Violation of symmetry==
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| [[File:Right left helicity.svg|thumb|right|280px|[[Chirality (physics)|Left- and right-handed particles]]: p is the particle's momentum and S is its [[Spin (physics)|spin]]. Note the lack of reflective symmetry between the states.]]
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| The [[physical law|laws of nature]] were long thought to remain the same under mirror [[reflection (physics)|reflection]], the reversal of all [[Euclidean space|spatial axes]]. The results of an experiment viewed via a mirror were expected to be identical to the results of a mirror-reflected copy of the experimental apparatus. This so-called law of [[parity (physics)|parity]] [[conservation law|conservation]] was known to be respected by classical [[gravitation]], [[electromagnetism]] and the [[strong interaction]]; it was assumed to be a universal law.<ref>{{cite book |title=American scientists |author=Charles W. Carey |chapter=Lee, Tsung-Dao |year=2006 |publisher=Facts on File Inc. |url=http://books.google.co.uk/books?id=00r9waSNv1cC&pg=PA225 |page=225 |isbn=9781438108070}}</ref> However, in the mid-1950s [[Chen Ning Yang]] and [[Tsung-Dao Lee]] suggested that the weak interaction might violate this law. [[Chien Shiung Wu]] and collaborators in 1957 discovered that the weak interaction violates parity, earning Yang and Lee the [[Nobel Prize in Physics#1950s|1957 Nobel Prize in Physics]].<ref>{{cite web |publisher=Nobel Media |work=NobelPrize.org |title=The Nobel Prize in Physics 1957 |url=http://nobelprize.org/nobel_prizes/physics/laureates/1957/ |accessdate=26 February 2011}}</ref>
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| Although the weak interaction used to be described by [[Fermi's theory]], the discovery of parity violation and [[renormalization]] theory suggested a new approach was needed. In 1957, [[Robert Marshak]] and [[George Sudarshan]] and, somewhat later, [[Richard Feynman]] and [[Murray Gell-Mann]] proposed a '''V−A''' ([[vector (geometry)|vector]] minus [[axial vector]] or left-handed) [[Lagrangian]] for weak interactions. In this theory, the weak interaction acts only on left-handed particles (and right-handed antiparticles). Since the mirror reflection of a left-handed particle is right-handed, this explains the maximal violation of parity. Interestingly, the '''V−A''' theory was developed before the discovery of the Z boson, so it did not include the right-handed fields that enter in the neutral current interaction.
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| However, this theory allowed a compound symmetry '''[[CP violation|CP]]''' to be conserved. '''CP''' combines parity '''P''' (switching left to right) with charge conjugation '''C''' (switching particles with antiparticles). Physicists were again surprised when in 1964, [[James Cronin]] and [[Val Fitch]] provided clear evidence in [[kaon]] decays that CP symmetry could be broken too, winning them the 1980 [[Nobel Prize in Physics]].<ref>{{cite web |publisher=Nobel Media |work=NobelPrize.org |title=The Nobel Prize in Physics 1980 |url=http://nobelprize.org/nobel_prizes/physics/laureates/1980/ |accessdate=26 February 2011}}</ref> In 1973, [[Makoto Kobayashi (physicist)|Makoto Kobayashi]] and [[Toshihide Maskawa]] showed that CP violation in the weak interaction required more than two generations of particles,<ref name="KM">
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| {{cite journal
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| |author=M. Kobayashi, T. Maskawa
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| |year=1973
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| |title=CP-Violation in the Renormalizable Theory of Weak Interaction
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| |journal=[[Progress of Theoretical Physics]]
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| |volume=49 |issue=2 |pages=652–657
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| |doi=10.1143/PTP.49.652
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| |bibcode = 1973PThPh..49..652K }}</ref> effectively predicting the existence of a then unknown third generation. This discovery earned them half of the 2008 Nobel Prize in Physics.<ref>{{cite web |publisher=Nobel Media |work=NobelPrize.org |title=The Nobel Prize in Physics 1980 |url=http://nobelprize.org/nobel_prizes/physics/laureates/2008/ |accessdate=17 March 2011}}</ref> Unlike parity violation, CP violation occurs in only a small number of instances, but remains widely held as an answer to the difference between the amount of matter and antimatter in the universe; it thus forms one of [[Andrei Sakharov]]'s three conditions for [[baryogenesis]].<ref>{{cite book |title=CP violation |editor=Cecilia Jarlskog |author=Paul Langacker |chapter=Cp Violation and Cosmology |year=1989, 2001 |publisher=World Scientific Publishing Co. |location=London, [[River Edge]] |url=http://books.google.co.uk/books?id=U5TC5DSWOmIC |page=552 |isbn=9789971505615}}</ref>
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| ==See also==
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| * [[Weakless Universe]] – the postulate that weak interactions are not [[Anthropic principle|anthropically necessary]]
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| ==References==
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| ===Citations===
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| {{reflist}}
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| ===General readers===
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| *{{Cite book
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| |author=R. Oerter
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| |year=2006
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| |title=The Theory of Almost Everything: The Standard Model, the Unsung Triumph of Modern Physics
| |
| |publisher=[[Plume (publisher)|Plume]]
| |
| |isbn=978-0-13-236678-6
| |
| }}
| |
| *{{Cite book
| |
| |author=B.A. Schumm
| |
| |year=2004
| |
| |title=Deep Down Things: The Breathtaking Beauty of Particle Physics
| |
| |publisher=[[Johns Hopkins University Press]]
| |
| |isbn=0-8018-7971-X
| |
| }}
| |
| | |
| ===Texts===
| |
| *{{Cite book
| |
| | author=D.A. Bromley
| |
| | year=2000
| |
| | title=Gauge Theory of Weak Interactions
| |
| | publisher=[[Springer (publisher)|Springer]]
| |
| | isbn=3-540-67672-4
| |
| }}
| |
| *{{Cite book
| |
| |author=G.D. Coughlan, J.E. Dodd, B.M. Gripaios
| |
| |year=2006
| |
| |title=The Ideas of Particle Physics: An Introduction for Scientists
| |
| |edition=3rd
| |
| |publisher=[[Cambridge University Press]]
| |
| |isbn=978-0-521-67775-2
| |
| }}
| |
| *{{Cite book
| |
| | author1=W. N. Cottingham
| |
| | author2=D. A. Greenwood
| |
| | title=An introduction to nuclear physics
| |
| | publisher=Cambridge University Press
| |
| | year=1986, 2001
| |
| | edition=2
| |
| | page=30
| |
| | isbn=978-0-521-65733-4
| |
| | url=http://books.google.co.uk/books?id=0VIpJPn-qWoC&pg=PA30
| |
| }}
| |
| *{{Cite book
| |
| | author=D.J. Griffiths
| |
| | year=1987
| |
| | title=Introduction to Elementary Particles
| |
| | publisher=[[John Wiley & Sons]]
| |
| | isbn=0-471-60386-4
| |
| }}
| |
| *{{Cite book
| |
| | author=G.L. Kane
| |
| | year=1987
| |
| | title=Modern Elementary Particle Physics
| |
| | publisher=[[Perseus Books]]
| |
| | isbn=0-201-11749-5
| |
| }}
| |
| *{{Cite book
| |
| | author=D.H. Perkins
| |
| | year=2000
| |
| | title=Introduction to High Energy Physics
| |
| | publisher=[[Cambridge University Press]]
| |
| | isbn=0-521-62196-8
| |
| }}
| |
| | |
| {{Fundamental interactions}}
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| | |
| {{Use dmy dates|date=March 2011}}
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| | |
| {{DEFAULTSORT:Weak Interaction}}
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| [[Category:Nuclear physics]]
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| [[Category:Electroweak theory]]
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| [[Category:Concepts in physics]]
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| | |
| {{Link GA|zh}}
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