Color charge

In particle physics, color charge is a property of quarks and gluons which are related to their strong interactions in the context of quantum chromodynamics (QCD). This has analogies with the notion of electric charge of particles, but because of the mathematical complications of QCD, there are many technical differences. The "color" of quarks and gluons have nothing to do with the visual perception of color, but is a whimsical name for a property which has almost no manifestation at distances above the size of an atomic nucleus.

Coupling constant and charge

In a quantum field theory the notion of a coupling constant and a charge are different but related. The coupling constant sets the magnitude of the force of interaction; for example, in quantum electrodynamics, the fine structure constant is a coupling constant. The charge in a gauge theory has to do with the way a particle transforms under the gauge symmetry, ie, its representation under the gauge group. For example, the electron has charge -1 and the positron has charge +1, implying that the gauge transformation has opposite effects on them in some sense. Specifically, if a local gauge transformation φ(x) is applied in electrodynamics, then one finds

Related Topics:
Quantum field theory - Coupling constant - Charge - Quantum electrodynamics - Fine structure constant - Gauge theory - Representation - Group - Electron - Positron - Gauge transformation

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::A_mu o A_mu+partial_muphi(x),   psi o exppsi  and  overlinepsi o expoverlinepsi

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where Aμ is the photon field, and ψ is the electron field with Q=-1 (a bar over ψ denotes its antiparticle— the positron). Since QCD is a non-Abelian theory, the representations, and hence the color charges, are more complicated. They are dealt with in the next section.

Related Topics:
Photon - Abelian

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