Electroweak interaction

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In particle physics, the electroweak interaction is the unified description of two of the four fundamental interactions of nature: electromagnetism and the weak interaction. Although these two forces appear very different at everyday low energies, the theory models them as two different aspects of the same force. Above the unification energy, on the order of 10² GeV, they would merge into a single electroweak force. Thus if it is hot enough (Big Bang hot, for example) then electromagnetic force and weak force will merge into electroweak.

Mathematically, the unification is accomplished under an SU(2) × U(1) gauge group. The corresponding gauge bosons are the photon of electromagnetism and the W and Z bosons of the weak force. In the Standard Model, the weak gauge bosons get their mass from the spontaneous symmetry breaking of the electroweak symmetry from SU(2) × U(1)_Y to U(1)_em, caused by the Higgs mechanism (see also Higgs boson). The subscripts are used to indicate that these are different copies of U(1); the generator of U(1)_em is given by Q = Y/2 + I₃, where Y is the generator of U(1)_Y (called the weak hypercharge), and I₃ is one of the SU(2) generators (a component of weak isospin). The distinction between electromagnetism and the weak force arises because there is a (nontrivial) linear combination of Y and I₃ that vanishes for the Higgs boson (it is an eigenstate of both Y and I₃, so the coefficients may be taken as −I₃ and Y): U(1)_em is defined to be the group generated by this linear combination, and is unbroken because it doesn't interact with the Higgs.

Image:E-W lagrangian.png

Lagrangian for the Electroweak interaction.

For contributions to the unification of the weak and electromagnetic interaction between elementary particles Abdus Salam, Sheldon Glashow and Steven Weinberg were awarded the Nobel Prize in Physics in 1979.^[1] The existence of the electroweak interactions was experimentally established in two stages: the first being the discovery of neutral currents in neutrino scattering by the Gargamelle collaboration in 1973, and the second in 1983 by the UA1 and the UA2 collaborations that involved the discovery of the W and Z gauge bosons in proton-antiproton collisions at the converted Super Proton Synchrotron.

1 Lagrangian
2 See also
3 References
- 3.1 Textbooks
- 3.2 Journal Articles

[edit] Lagrangian

Sander Bais' description of the electroweak lagrangian as four terms^[2]:

The g term describes the interaction between the three W particles and the B particle.
The f term describes the interaction between the electrons, muons, and quarks (the Dirac particles) of the Standard Model. The subscripts Li and Ri in <math>\psi_{Li}</math> and <math>\psi_{Ri}</math> refer to the Left and Right-handed spin of the i-th species of Dirac particles in the Standard Model. This is reflected in the asymmetric form of this term.
The H term describes the Higgs field Φ.
The m term gives the mass generated by the interaction of the Higgs with the other varieties of particles given in the Lagrangian.

[edit] See also

[edit] References

^ Sander Bais (2005), The Equations. Icons of knowledge ISBN 0-674-01967-9 p 84
^ Sander Bais (2005), The Equations. Icons of knowledge ISBN 0-674-01967-9 pp 84-87

[edit] Textbooks

Griffiths, David J. (1987). Introduction to Elementary Particles. Wiley, John & Sons, Inc. ISBN 0-471-60386-4.

D.A. Bromley (2000). Gauge Theory of Weak Interactions. Springer. ISBN 3-540-67672-4.

Gordon L. Kane (1987). Modern Elementary Particle Physics. Perseus Books. ISBN 0-201-11749-5.

[edit] Journal Articles

S.F. Novaes, Standard Model: An Introduction, hep-ph/0001283
D.P. Roy, Basic Constituents of Matter and their Interactions — A Progress Report, hep-ph/9912523
Y. Hayato et al., Search for Proton Decay through p → νK⁺ in a Large Water Cherenkov Detector. Phys. Rev. Lett. 83, 1529 (1999).
Ernest S. Abers and Benjamin W. Lee, Gauge theories. Physics Reports (Elsevier) C9, 1-141 (1973).
J. Hucks, Global structure of the standard model, anomalies, and charge quantization, Phys. Rev. D 43, 2709–2717 (1991). [1]