# Questions tagged [parity]

Parity inversion P amounts to the sign flip of an odd number of coordinates (reflection). A parity-symmetric theory conserves P; since P²=I, the eigenvalues of P are 1 or -1. May be also used for formally analogous global, discrete, Z₂ symmetries, such as R- or G-parity.

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### Explain this step (related to gamma matrices and parity operator)

I am having hard time reproducing a step from the textbook "Lecture Notes on Quantum Field Theory", by Ashok Das. On page 429 ( above equation 11.72), the author is talking about the parity ...
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### A question about space inversion symmetry of parity in a rotated disk

In a rotated disk (say, Faraday disk), is the space inversion symmetry of parity still preserved?
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### Is really hermiticity necessary to be a physical observable? What about larger class of operators like PT invariant operators or pseudo hermitian one?

It's really necessary for an observable represented by an operator acting in a Hilbert space to be hermitian? It's known that not only hermitian operators have real eigenvalues and that also normal ...
1 vote
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### What is the correct inversion symmetry in a two-band model

Consider a simple two-band tight-binding model $$H(k)=\sin{k_x}\,\sigma_x+\sin{k_y}\,\sigma_y + \left(\sum_{i=x,y,z}\cos{k_i}-2\right)\sigma_z.$$ Let's assume $H$ is for real spins. It breaks the time-...
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### Parity symmetry complete/detailed definition and the group elements

I am trying to write down a complete/detailed definition for the parity symmetry. Symmetry as a concept is different in mathematics and in physics. There are also many other concepts which differ in ...
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### How is parity measured experimentally?

I'm reading Wong 'Introductory Nuclear Physics' and in chapter 3-1 he writes that "For the deuteron, it is known that the parity is positive. Let us see what we can learn from this piece of ...
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### How many degrees of freedom does a photon have in 2+1D?

Wigner's classification of particles implies that the internal degrees of freedom of a particle transform under unitary representations of the subgroup of the Lorentz group that leaves its momentum ...
1 vote
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### Gamma Ray Emission in the Wu Experiment

In the classic Wu experiment (https://doi.org/10.1103/PhysRev.105.1413) parity violation was discovered in the weak interaction through the asymmetry in the distribution of electrons in the beta decay ...
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### How does parity conservation follow from the Wu experiment?

The Wu experiment shows how parity symmetry does not hold for the weak force. However, how does this proof that parity conservation also doesn't hold? If my understanding is correct, the absence of ...
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### How can scalar mesons have even parity?

From my understanding a pseudo-scalar meson has: $$J^P=0^-$$ That makes sense since the total spin $S=0$ and $l$ must be $l=0$ which makes the parity: $$P=(-1)^{l+1}=-1$$ uneven. Now, for scalar ...
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### Consistency of One-Pion Exchange with Selection Rules for NN Pion Production (in Chiral EFT, e.g.)

Hope you're ready for a long question, but I think quite an interesting one! One-pion exchange is an established nucleon-nucleon potential which is well-defined for any joint angular momentum state of ...
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### Does particle parity play any role in matter anti-matter annihilation?

If a left handed electron and a right handed antimatter electron were to meet, would they still annihilate? In the same way, if a left handed electron and a left handed antimatter electron meet, will ...
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### Why the eigenstate of an even observable is an eigenstate of the parity operator?

Definition of an even observable: $B_+=\Pi B_+\Pi$, where $\Pi$ is the parity operator. Consider an arbitrary even observable $B_+|\psi_b\rangle=b|\psi_b\rangle$, then $|\psi_b\rangle$ is an ...
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