Does charge conjugation affect parity?

silmaril89
Messages
85
Reaction score
0
"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 \psi \to \psi_c = \gamma^2 \psi^\ast):

Suppose \psi is left-handed (i.e. P_L \psi = \psi and P_R \psi = 0), then
P_L \psi_c = P_L \gamma^2 \psi^\ast = \gamma^2 P_R \psi^\ast = \gamma^2 (P_R \psi)^\ast = 0
and
P_R \psi_c = P_R \gamma^2 \psi^\ast = \gamma^2 P_L \psi^\ast = \gamma^2 (P_L \psi)^\ast = \psi_c
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?
 
Physics news on Phys.org
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##,
\Psi=\pmatrix{\chi\cr\xi^\dagger}
The charge conjugate field is then
\Psi^c=\pmatrix{\xi\cr\chi^\dagger}
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.
 
  • Like
Likes silmaril89
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.
 
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. Towards the end of the first lecture for the Qiskit Global Summer School 2025, Foundations of Quantum Mechanics, Olivia Lanes (Global Lead, Content and Education IBM) stated... Source: https://www.physicsforums.com/insights/quantum-entanglement-is-a-kinematic-fact-not-a-dynamical-effect/ by @RUTA
If we release an electron around a positively charged sphere, the initial state of electron is a linear combination of Hydrogen-like states. According to quantum mechanics, evolution of time would not change this initial state because the potential is time independent. However, classically we expect the electron to collide with the sphere. So, it seems that the quantum and classics predict different behaviours!
Back
Top