charge conjugation

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (December 2008)

It has been suggested that this article or section be merged with C parity. (Discuss)

In physics, C-symmetry means the symmetry of physical laws under a charge-conjugation transformation. Electromagnetism, gravity and the strong interaction all obey C-symmetry, but weak interactions violate C-symmetry maximally.

Charge Reversal in Electromagnetism

The laws of electromagnetism (both classical and quantum) are invariant under this transformation: if each charge q were to be replaced with a charge -q and the directions of the electric and magnetic fields were reversed, the dynamics would preserve the same form. In the language of quantum field theory, charge conjugation transforms:^{[citation needed]}

Notice that these transformations do not alter the chirality of particles. A left-handed neutrino would be taken by charge conjugation into a left-handed antineutrino, which does not interact in the Standard Model. This property is what is meant by the "maximal violation" of C-symmetry in the weak interaction.

(Some postulated extensions of the Standard Model, like left-right models, restore this C-symmetry.)

Combination of Charge and Parity Reversal

It was believed for some time that C-symmetry could be combined with the parity-inversion transformation (see P-symmetry) to preserve a combined CP-symmetry. However, violations of even this symmetry have now been identified in the weak interactions (particularly in the kaons and B mesons). In the Standard Model, this CP violation is due to a single phase in the CKM matrix. If CP is combined with time reversal (T-symmetry), the resulting CPT-symmetry can be shown using only the Wightman axioms to be universally obeyed.

Charge Definition

To give an example, take two real scalar fields, φ and χ. Suppose both fields have even C-parity (even C-parity refers to even symmetry under charge conjugation ex. Cψ(q) = Cψ( − q), as opposed to odd C-parity which refers to antisymmetry under charge conjugation ex. Cψ(q) = − Cψ( − q)). Now reformulate things so that . Now, φ and χ have even C-parities because the imaginary number i has an odd C-parity (C is antiunitary).

In other models, it is possible for both φ and χ to have odd C-parities.^{[clarification needed]}

References

• Sozzi, M.S. (2008). Discrete symmetries and CP violation. Oxford University Press. ISBN 978-0-19-929666-8. 

See also

• anti-particle
• antimatter