C-symmetry

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

Related Topics:
Charge - Transformation - Standard Model - Left-right model

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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:

Related Topics:
Electromagnetism - Classical - Quantum - Invariant - Electric - Magnetic field - Quantum field theory

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• $A^mu\; ightarrow\; -A^mu$

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.

Related Topics:
Chirality - Neutrino - Antineutrino

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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.

Related Topics:
Parity - P-symmetry - CP-symmetry - Kaon - Meson - CP violation - CKM matrix - T-symmetry - CPT-symmetry - Wightman axioms

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There is really a lot of ambiguity and arbitrariness in the definition of charge conjugation. To give an example, take two real scalar fields, φ and χ. Formulated as it is, both fields have even C-parity. Now reformulate things so that psiequiv {phi + i chiover sqrt{2}}. Now, φ has an even C-parity whereas χ has an odd C-parity. But let's redefine psiequiv {chi + iphioversqrt{2}}. Now it's the other way around. Similarly, a complex Weyl spinor can be reexpressed as a real Majorana spinor and vice versa. This arbitrariness allows physicists to define C the way it is in left-right models.

Related Topics:
Weyl spinor - Majorana spinor - Left-right model

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