Charge conjugation

Charge conjugation is a transformation that replaces particles with antiparticles and reverses their additive internal charges. In quantum field theory, it is represented by an operator acting on fields or states.

Charge-conjugation operator: An operator that maps particle states or fields to their charge-conjugate counterparts. It implements the transformation on quantum states and fields.
C-parity: The eigenvalue, usually +1 or −1, of a neutral state under charge conjugation. It labels neutral particle states when charge conjugation is a symmetry.
Parity (physics): A spatial transformation that reverses all coordinates through the origin. Parity reverses spatial orientation, whereas charge conjugation exchanges particles and antiparticles.
Electric charge: A conserved property of matter that determines its electromagnetic interactions. It is the familiar additive charge that changes sign under charge conjugation.
Antiparticle: A particle with the same mass as its corresponding particle and opposite additive charges. Charge conjugation maps each particle to its corresponding antiparticle.
Positronium: A short-lived bound state of an electron and a positron. Its charge-conjugation eigenvalue determines whether it can decay into an even or odd number of photons.
Time reversal symmetry: A symmetry that reverses the direction of time in the equations of motion. It changes the time coordinate rather than internal particle charges.
Quantum field theory: A framework that describes particles as excitations of fields and incorporates quantum mechanics with special relativity. Charge conjugation is formulated as a transformation of quantum fields and states.
Dirac field: A quantum field describing spin-one-half particles, such as electrons, and their antiparticles. Its charge-conjugate field exchanges particle and antiparticle components.
Selection rule: A constraint that determines whether a transition or reaction is allowed by a physical symmetry. Conservation of charge-conjugation parity forbids some decays and transitions.

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