is a property of a system or theory where the combined charge conjugation (replacing particles with their anti-particles) and parity (reversing the sign of every vector, equivalent to reflecting the system through the origin) operations yield non-equivalent results. Only the weak interaction is know to produce CP-violation.
Questions tagged [cp-violation]
165 questions
51
votes
3 answers
Do pear-shaped nuclei really have anything to do with time travel?
Recently (in the last week or two), various articles about pear shaped nuclei have appeared, such as this one from Science Alert and this from the BBC
The Science Alert article includes the quote
We've found these nuclei literally point towards a…
Matt
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26
votes
1 answer
What is the status of Witten's and Vafa's argument that the QCD vacuum energy is a minimum for zero $\theta$ angle?
The argument, which I reproduce here from Ramond's `Journies BSM', is originally by Witten and Vafa in ($\it{Phys}$. $\it{Rev}$. $\it{Lett}$. 53, 535(1984)). The argument is that for $\theta = 0 $ (mod $2\pi$) the QCD vacuum energy $E(\theta)$ is…
DJBunk
- 3,788
25
votes
3 answers
Why do we care about chirality?
I'm trying to figure out what's the importance of chirality in QFT. To me it seems just something mathematical (the eigenvalue of the $\gamma^{5}$ operator ) without any physical insight in it. So my question is why do we care about Chirality, and…
Mathew
- 781
23
votes
2 answers
Yang-Mills CP violation
Why does a term proportional to $\left(F,\,\tilde{F}\right)\propto Tr\left[ F_{\mu\nu}\tilde{F}^{\mu\nu}\right]$ in the Lagrangian of the pure Yang-Mills theory violate CP?
PPR
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17
votes
5 answers
Matter-Antimatter Asymmetry in Experiments?
As I hope is obvious to everyone reading this, the universe contains more matter than antimatter, presumably because of some slight asymmetry in the amounts of the two generated during the Big Bang. This raises the question of whether there are any…
Chad Orzel
- 8,646
17
votes
1 answer
Origin of phases in amplitudes in QFT
Amplitudes in QFT are typically real. I'd like to understand the physical meaning of an amplitude having a phase. I know of three ways that amplitudes can get a phase:
If the couplings have an imaginary component
If there is a trace over the spin…
JeffDror
- 9,093
14
votes
1 answer
Baryogenesis only at the Planck scale, or none at all?
I can think of three general ways of explaining why the universe contains more matter than antimatter:
(1) Near the Planck time, the universe had zero baryon asymmetry, but at some later time, determined by some GUT energy scale, the Sakharov…
user4552
14
votes
1 answer
Theta parameter of QCD: Very small, periodic in $2\pi$ or both?
I've been learning about the theta parameter of QCD and I'm confused about the fact that it's supposed to be very small but at the same time some sources say that the Yang-Mills theory should be invariant to 2$\pi$ shifts in $\theta$
Sources that…
Siraj R Khan
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14
votes
4 answers
Regarding matter-antimatter asymmetry
We all know that the asymmetry between matter and antimatter is a big puzzle in physics. But I don't know why one expects matter-antimatter symmetry in the first place? As in, is there a fundamental principle which suggests that matter and…
Ayush Raj
- 469
14
votes
2 answers
Topological susceptibility
In QCD we have strong CP violation (and hence a $\theta$-dependence of the theory) only if the topological susceptibility of the vacuum is nonzero:
$$\langle F\tilde{F},F\tilde{F}\rangle_{q \rightarrow 0} =\text{const} \neq 0,$$
where $F$ is the…
Thomas
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14
votes
1 answer
The Ozma Problem
The "Ozma problem" was coined by Martin Gardner in his book "The Ambidextrous Universe", based on Project Ozma. Gardner claims that the problem of explaining the humans left-right convention would arise if we enter into communication (by radio…
kuzand
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13
votes
1 answer
CP violation from the Electroweak SU(2)$_{weak,flavor}$ by $\int \theta F \wedge F $
Question: Why there is NO Charge-Parity (CP) violation from a potential Theta term in the electroweak SU(2)$_{weak,flavor}$ sector by $\theta_{electroweak} \int F \wedge F$?
(ps. an explicit calculation is required.)
Background:
We know for a…
wonderich
- 8,086
13
votes
3 answers
If the protons in a nucleus were replaced by antiprotons and the electrons by positrons what fundamental change would be introduced into the universe?
Exactly what the question says;
If all the protons and electrons in every single atom in the universe were swapped for their anti-particles, what would essentially change?
Safiul
- 468
12
votes
1 answer
axion couplings
As I understand it, the axion $a$ originates from the spontaenous symmetry breaking of $U(1)_{PQ}$. This symmetry being anomalous, and because of the QCD vacuum structure, a non vanishing term like $\frac{a}{f_a}Tr( G \tilde{G})$ is included in the…
user42865
- 389
11
votes
1 answer
CP Violation of the CKM Matrix
Considering the relation between the $SU(2)_{WEAK}$ partners of the $|u \rangle$, $|c \rangle$, and $|t \rangle$ mass eigenstates and the corrseponding downtype eigenstates
$
\left(
\begin{array}{c}
J_{WEAK}^{-}|u \rangle\\
…
Dilaton
- 9,771