Does charge conjugation affect parity?

In summary: I'm going to try to work through your stuff and do some more research. If I have any more questions, I'll post them back here. Thanks again!In summary, there is a difference in the way the two statements are presented, but they are both technically correct. The charge conjugate of a left-handed field can be either a left-handed or right-handed field, depending on the basis used. This difference in notation can lead to confusion and requires further investigation for a complete understanding.
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silmaril89
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"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." --https://en.wikipedia.org/wiki/C-symmetry

The excerpt above seems to unambiguously answer this question. But, then:

"You can easily convince yourself (exercise II.1.9) that the charge conjugate of a left handed field is right handed and vice versa." --Quantum Field Theory in a Nutshell, A. Zee

These statements appear to be contradictory. What's going on here?

Also, it does seem easy to convince myself of Zee's comment (following Zee's convention that [itex]\psi \to \psi_c = \gamma^2 \psi^\ast[/itex]):

Suppose [itex]\psi[/itex] is left-handed (i.e. [itex]P_L \psi = \psi[/itex] and [itex]P_R \psi = 0[/itex]), then
[tex]P_L \psi_c = P_L \gamma^2 \psi^\ast = \gamma^2 P_R \psi^\ast = \gamma^2 (P_R \psi)^\ast = 0[/tex]
and
[tex]P_R \psi_c = P_R \gamma^2 \psi^\ast = \gamma^2 P_L \psi^\ast = \gamma^2 (P_L \psi)^\ast = \psi_c[/tex]
Therefore, it appears that Zee's comment is correct. Can anyone help me understand why the two quotes above are or are not in contradiction?
 
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  • #2
Both statements are technically true, but I think Zee's is misleading. If we work in basis where ##\gamma_5## is diagonal, then a Dirac field ##\Psi## can be written as a left-handed Weyl field ##\chi## stacked on top of a right-handed Weyl field ##\xi^\dagger##,
[tex]\Psi=\pmatrix{\chi\cr\xi^\dagger}[/tex]
The charge conjugate field is then
[tex]\Psi^c=\pmatrix{\xi\cr\chi^\dagger}[/tex]
Now if we set ##\xi=0##, then we recover Zee's statement (and your algebra). But I think it is more correct to say that the charge conjugate of the left-handed field ##\chi## is the left-handed field ##\xi##. Then, if we use ##\Psi## as a Dirac field for neutrinos, ##\chi## creates left-handed neutrinos, and ##\xi## creates left-handed antineutrinos, which is consistent with the wikipedia statement.
 
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Ok, thanks for the reply. I think I'm still a little confused, but you've put me in a particular direction to begin investigating this further.
 

1. What is charge conjugation?

Charge conjugation is a fundamental symmetry transformation in particle physics that changes a particle into its antiparticle. It involves swapping the charges of all the particles in a system, such as changing a positively charged particle into a negatively charged one.

2. What is parity?

Parity is another fundamental symmetry transformation that involves changing the spatial coordinates of a particle or system. It essentially reflects the system across a plane, similar to looking at a mirror image.

3. How does charge conjugation affect parity?

In general, charge conjugation and parity are two separate symmetry transformations and do not affect each other. However, in some cases, such as in strong and electromagnetic interactions, the combination of the two transformations may result in a new symmetry known as charge parity (CP) symmetry.

4. What is CP violation?

CP violation occurs when the combined charge parity symmetry is not conserved, meaning that the laws of physics are not symmetrical under the combined transformation of charge conjugation and parity. This phenomenon was first observed in experiments involving the decay of neutral kaons in the 1960s.

5. Why is the study of CP violation important?

CP violation is an important topic in particle physics as it may help explain the dominance of matter over antimatter in the universe. It also plays a crucial role in understanding the early universe and the origin of the universe's asymmetry. Additionally, studying CP violation can provide insight into the fundamental laws of physics and may lead to the discovery of new particles and interactions.

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