Questions tagged [cp-violation]

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.

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153 views

$CP$ Invariance of Yang-Mills Vacua in Electroweak Theory

It is well know that quantum Yang-Mills theory has a periodic vacuum structure. Consider electroweak theory. For a single generation of fermions, the theory is CP invariant. I would like to know if ...
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Why does the axion solve the CP problem?

I don't understand why the CP violating term in QCD vanishes when we introduce the axion. The term is $$\left(\frac{a}{f_a}+\theta\right)G\tilde{G}$$ It is claimed that $\left\langle a\right\rangle=-\...
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Is there violation of energy conservation when a particle transforms to its anti-particle, for example $B^0\to\bar{B}^0$, or $K^0\to\bar{K}^0$

additive information : $B^0$ and $\bar{B}^0$ don't have the same mass, $K^0$ and $\bar{K}^0$ don't have the same mass. is there energy violation? if yes, is the key explanation of this coming from the ...
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CP violation measurement

I have a question regarding the measurement of CP Violation in experiment. How is parity measured in an experiment? I know that in the direct measurement of CP violation we look at a particle process ...
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Detail on C vs. CP violation

In the answer given by knzhou to the post What distinguishes the behaviour of particle from its antiparticle: C violation or CP violation? it is said that "but the reaction $i \rightarrow f$ will ...
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How do we see that the axion is a pseudoscalar?

The axion is the pseudo-Goldstone boson associated to the breaking of the conjectured Peccei-Quinn Abelian symmetry. The axion couples to the SM gauge fields in a CP-invariant manner (e.g. $aF\tilde F ...
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Antiparticles, CPT and leptogenesis

When people are being careful they'll tell you that antiparticles are the CPT conjugates of particles. You can't say that they are C conjugates or CP because these, while they do reverse the charge, ...
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Is a constant electric field CP violating?

Consider, for instance, a fundamental massless three-form field $C_{\alpha\beta\gamma}$ in the Coulomb phase: $$ \mathcal L = E_{\mu\alpha\beta\gamma}E^{\mu\alpha\beta\gamma} + C_{\alpha\beta\gamma}J^...
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CP-symmetery conservation

How can one show that for a given decay, say $\pi^+ \rightarrow \nu_\mu + \mu^+$, CP-symmetry is conserved or violated? Is there a visual way of doing such?
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Symmetry in a sketch of the Wu experiment

On Wikipedia the Wu experiment is explained by the sketch below It is stated, that the mirrored experimental setup should include a coil with winding in opposite direction to the original coil, but ...
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The strong CP problem in Grand Unified Theories

The strong CP problem could, in principle, be solved by a massless up quark. Can this solution be embedded in Grand Unified Theories, such as $SO(10)$ (or $SU(5)$)? These theories, in particular $SO(...
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Can the CKM matrix supply the CP asymmetry as required by baryogenesis, in principle?

In the process of Baryogenesis through Leptogenesis from the decay of heavy Majorana neutrinos, the necessary CP violation is perhaps provided only by the CP phases in the PMNS matrix. But the Weak ...
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How does the global $G^2G'$ anomaly make all the $\theta$-vacua associated to the gauge group $G$ physically equivalent?

Consider a gauge group $G$ and suppose that there is a $\theta$-term associated to it. According to this answer, the existence of a global anomalous symmetry $G'$ which rotates the $\theta$-term, ...
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What does $B+L$ anomaly have to do with a phase redefinition of the left-handed quark field?

According to this answer, the reason why $SU(2)_L$ weak theory does not have a theta vacuum is because any theta term can be reabsorbed with a phase redefinition of the left-handed quark field. ...
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Does the weak force obey the CPT symmetry? How?

I have read that the weak force does not obey the charge symmetry, the parity symmetry, and the time reversal symmetry. Then how does it obey the CPT symmetry?
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How can spontaneous $P$ or $CP$ violation arise? Examples needed

In quantum field theory, there can be a spontaneous breakdown of discrete and continuous symmetries. Can there be a spontaneous breakdown of P and CP violation where P represents parity and C ...
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What distinguishes the behaviour of particle from its antiparticle: C violation or CP violation?

It is said that a CP violation would mean that the behaviour of the particle is different from the behaviour of antiparticle. Why is C violation not good/enough?
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What is unsolved in CP Violation?

I learnt about CP Violation in my Quantum Information Theory and Particle Physics courses. However I have not understood what exactly has not been solved yet about CP Violation. I thought that the ...
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About the asymmetry of baryons

I don't understand why CP violation is insufficient to explain the observed baryon asymmetry? And how do you solve it using the lepton sector? Key Words: CKM - Cabibbo-Kobayashi-Maskawa Matrix: in ...
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Parity violation

I've been reading on wikipedia about parity violation in the weak force and the conclusion is: This implies that parity is not a symmetry of our universe, unless a hidden mirror sector exists in ...
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CP Phases in the PMNS Matrix

I am interested in how to derive the correct number of CP violating phases in the neutrino mixing matrix (or PMNS matrix). My approach is the following. By hypothesis, the neutrino mixing is given by ...
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Dependence of decay width on the CKM parameters

So what i want to know mainly is when do i use the conjugate? Like when should it be $V_{cd}$ or $V^*_{cd}$? Please look at a pic for example - So should I used conjugate? $V^*$ instead of $V$? ...
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Does reversing time give parity reversed antimatter or just antimatter?

Feynman's idea states that matter going backwards in time seems like antimatter. But, since nature is $CPT$ symmetric, reversing time ($T$) is equivalent to $CP$ operation. So, reversing time gives ...
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Can experiments measure the Majorana phases?

Unlike the Dirac CP-phase $\delta$, the Majorana CP-phases $\alpha,\beta$ do not appear in the formula of neutrino flavour oscillation probability. Hence, they cannot be measured from oscillation ...
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What is the meaning of the Wilson coefficients $C_{S,P,T}$ in the electron-nucleon interaction?

I am doing a project on electric dipole moments in supersymmetry. My background is in high energy physics, so I am having trouble fully grasping the nuclear interactions. Part of that includes ...
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Why is there not enough CP violation to account for baryogenesis in the SM?

One of Sakharov conditions states that both C and CP symmetries must be violated by a theory which includes any baryogenesis mechanism. The Standard Model happens to be such a theory, and happens to ...
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C, P and CP in particle physics

We know that the charge conjugation (C) and parity (P), both are violated maximally in particle physics. Then what is the need for looking for CP symmetry in order to distinguish matter from ...
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Why is $|\bar{K}^0\rangle=\mathscr{CP}|K^0\rangle$ and not $|\bar{K}^0\rangle=\mathscr{C}|K^0\rangle$?

If the charge conjugation operator $\mathscr{C}$ changes a particle state into the corresponding anti-particle state then we must write $|\bar{K}^0\rangle=\mathscr{C}|K^0\rangle$. But instead, we ...
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What is the correct definition of the Jarlskog invariant?

In this lecture on neutrino physics, Prof. Feruglio defines the Jarlskog invariant as $$J=\text{Im}(U_{\alpha i}^{*} U_{\beta i} U_{\alpha j} U_{\beta j}^{*})\tag{1}$$ where $U$ is the neutrino mixing ...
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Trying to work out the CP-transformation property of the Higgs potential

The parity transformation property of a complex scalar field $\phi(x)$ is given by: $$P\phi(t,\textbf{x}) P^{-1}=\eta_P\phi(t,-\textbf{x})$$ where $\eta_P=\pm 1$. The charge conjugation property of a ...
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Aliens from antimatter region

If we established a radio contact with an extraterrestrial civilization, assuming the signal latency permits, what question would we ask them to know if they are made of matter or anti-matter? I ...
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What are the anti-neutrino flavour oscillation formulae?

All the textbooks and references that I have come across give the neutrino 3-flavor oscillation formulae. However, the formulae for antineutrino oscillations are never given. Is it possible to derive ...
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What is the most natural way in which the Jarlskog invariant makes its appearance?

What is the most natural way in which the Jarlskog invariant can be introduced? I have seen ad hoc definitions given as $$J_{CP}=\text{Im}(V_{us}V_{cb}V^*_{ub}V^*_{cs})\tag{1}$$ which, to me, appears ...
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Why CP violation explains matter-antimatter asimmetry?

I'm studying Kaon oscillations and the Cronin & Fitch experiment on CP violation. I think I understand why CP is violated in the process but I don't understand why it means that matter and ...
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1answer
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How does one measure anti-neutrino flavor oscillation probabilities?

The Dirac $CP$ phase $\delta_{CP}$ in the $U_{PMNS}$ mixing matrix lead to the $CP$-violation in the Lepton sector. I think this can be tested by comparing neutrino flavour oscillation probabilities ...
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Consequence of C and CP-violation: What does it ensure and what it does not?

This question is a continuation of one of my earlier posts here and the accepted answer. Consider a two-body hypothetical decay $p^+\to e^+\gamma$ in a quantum field theory (say, a GUT). If the ...
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Difference between “C-violation without CP-violation” and “C-violation with CP -violation”

Consider two possible decay channels of a massive particle as $X\to A+B$ and $X\to C+D$ with decay rates $r$ and $1-r$ respectively. Let the decay rates of its antiparticle into channels $\bar X\to \...
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Do we know whether the “electron” neutrino is lighter than the “muon” neutrino?

The labeling of the neutrino mass eigenstates is arbitrary [PDG Neutrino Review]. Regularly it is assumed for convenience that $$\Delta m^2_{21} = m_2^2 - m_1^2 > 0.$$ Then, values for the mixing ...
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How to find the CP violating effective operator?

I've been meeting with one not-very-small problem in arriving at (3.3) in Shaposhnikov's "Structure of the high temperature gauge ground state and electroweak production of the barygon asymmetry" (...
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1answer
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hadronic matrix element for four quark condensate?

I am looking at the neutral kaon mixing in SM where calculation of a four quark condensate between Kaon and anti-Kaon is required, in order to obtain the kaon mass difference. $$\langle K| [ \bar{d}\...
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Does Leptogenesis require lepton number violating vertices?

One of the Sakharov condition for Baryogenesis requires Baryon number violating interactions in the theory. However, it is also possible to generate a baryon asymmetry via a lepton asymmetry or ...
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Kaon oscillations

Neutral Kaons CP eigenstates can be built as following: $$|K_1\rangle=\frac{|K^0\rangle-\bar{|K^0\rangle}}{\sqrt{2}}$$ $$|K_2\rangle=\frac{|K^0\rangle+\bar{|K^0\rangle}}{\sqrt{2}}$$ So that we ...
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How to understand CP-violation in kaon systems with Feynman diagrams and matrix elements?

I am trying to understand CP-Violation in the Kaon system using feynman diagrams and matrix element. Here is a slide from Mark Thomson corresponding exactly to what I am looking for (http://www.hep....
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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 ...
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Can CP-violation arise due to interference between two tree-level diagrams in a QFT?

In Leptogenesis, CP-asymetry arises due to the interference of the tree-level amplitude $N\rightarrow l_\alpha\phi$ (where $N$ is heavy sterile neutrino, $l_\alpha$ is a lepton flavour, and $\phi$ is ...
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Understanding CP-violation from a toy model of two fermions and a scalar boson

Consider a field theory given by the following Lagrangian $$\mathcal{L}_{int}=y\overline{\psi_1}\psi_2\phi+y^*\overline{\psi}_2\psi_1\phi^\dagger$$ where $\phi$ is a complex scalar field, and $\psi_1,\...
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Does the vacuum have a zero Seebeck coefficient?

I was considering how at very high energies (e.g the Schwinger Limit) the vacuum starts having properties we would normally associate with "materials", such as non-linear polarizibility. The Seebeck ...
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1answer
530 views

C-parity violation evidence

I know about the CP-violation experiments from the 60's and the P-violation from the 50's. But, is there a similar experiment which displays (perhaps historically in the same way as the experiements ...
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1answer
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Is CP problem the problem?

I've heard an argument that the question of smallness of QCD $\theta$ parameter is called the problem (namely, strong CP problem), since the other dimensionless couplings (like $\alpha_{s}$), are of ...
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CP violation in B meson system through mixing

Mathematically, $\left|\Gamma_{12}\right|<<\left|M_{12}\right|$ implies $\left|q/p\right|=1$,i.e there is no CP violation due to mixing. Please explain why it happens beyond this mathematical ...