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The Standard Model - Electroweak Force


The ElectroWeak Force - One of the major goals of elementary particle science is showing that even though particles may interact in somewhat different ways, they are ultimately controlled by the same guiding principles. During the early part of the 20th century, as the first particles were discovered, the forces acting on them were eventually classified as electromagnetic, weak nuclear, and strong nuclear. As time went on, scientists realized that the electromagnetic and weak nuclear forces were really one and the same force. The electroweak force fully explains the interactions (very well) of all the known leptons at the energy scales attainable so far.

It is hard to detect this at small energies, but as accelerators allowed the scientists to use more energetic interactions, the evidence became clear that forces would unify at a larger energy. On the other hand, a difficulty arose in that the gauge bosons or force carrying particles of the weak nuclear force have large masses. The force carrying particle of the electromagnetic force is the photon which is massless. Since it is massless, two bare electric charges can interact over an infinite distance (if they are the only charges around). The weak nuclear force can only act over a distance on the order of magnitude of the nuclear size.

Both the electromagnetic and weak force arise from gauge theories. This means the particles are "representations of a group" - or they define a mathematical structure whose elements interact in a definite way governed by the transformations of the groups. When two different groups are combined together, they don't always form a composite group. In the electroweak case, fortunately, they do.

One of the interesting phenomenon about this force is CP violation. This is one of the spacetime symmetries which is violated at the energies seen in the lab and has been experimentally observed but is postulated to be recovered as very high energies are attained. The mechanism by which the violation is thought to occur is by a Goldstone boson known as the Higgs particle. Through the process, both the weak force carriers (W+,W-,Z), and the Higgs boson itself acquire a (large) mass.

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last modified 2/28/2001   email Fermilab