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Questions tagged [color-charge]

The charge of the strong nuclear force is called "color". DO NOT USE THIS TAG for ordinary visible colors.

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Is color charge internal symmetry or global symmetry?

I was told the color charge in the standard model could not be observed directly. This sounded like the gauge field $\vec A$ in the electromagnetism. However, it is a discrete charge and does have ...
ShoutOutAndCalculate's user avatar
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$SU(3)$ color charge

Is the color charge the Noether charge due to the "global" $SU(3)$ symmetry of the QCD Lagrangian, or is it due to the "local" symmetry of the QCD Lagrangian?
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Colour Factor in QCD Pair Annihilation

My question occurred when I was reading Introduction to Elementary Particles by David J. Griffiths. In chapter 8, part 8.5, he is calculating the colour factor of quark-antiquark annihilation. My ...
quantumology's user avatar
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When can colour charge indices be equated?

I'm currently studying QFT and QCD for the first time and I have a question about the colour charge indices given below. I was asked the following question: (a) Derive the Feynman rule for the 3-...
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Confusion about EM absorption [duplicate]

I have now encountered various explanations on how matter interacts with electromagnetic waves (EM) but it still seems like an unconnected mess. The best way I can demonstrate my questions is with an ...
shar's user avatar
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Confusion about irreps of $SU(N)$: is the "color charge" the same as spin 1?

Sorry if the question is too silly or not well stated, I am happy to clarify any point. Also, my presuppositions can be wrong. Consider a system of spin-$s$ particles: their spin operators $S_x$, $S_y$...
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Is there a spin-1/2 hadron composed entirely of up quarks? [duplicate]

I am curious to know if there exists a spin-1/2 hadron that is composed of three up quarks. I understand that in quantum chromodynamics, baryons are formed of three quarks, each carrying a distinct ...
jkcwioqnkfdsoia's user avatar
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What does conservation of color charge mean for mixed states in QCD?

In quantum chromodynamics, in an interaction in which a quark and an anti-quark exchange a gluon, the color charge must be conserved. When we are talking about base states like $r\bar{b}$ it seems ...
Felipe S's user avatar
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Is colour the conserved charge of global $SU(3)$ color symmetry?

Consider the Lagrangian consisting of three Dirac fields $$ \mathcal{L} = \sum_{a=1}^3 \bar{\psi}_a ( i \gamma^\mu \partial_\mu - m ) \psi_a$$ where $a$ is an internal index labelling the colour ...
Hermitian_hermit's user avatar
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Quantum Chromodynamics and Group Theory

I know nothing of QCD, but I was watching this youtube video and pondered on whether the additive structure described is a group, and if so, which is it? As of now, I know the group must contain the ...
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Justifying the identification of eight gluons with the ${\bf 8}$ from ${\bf 3}\otimes{\bf 3}^*$

When we combine the fundamental ${\bf 3}$ and antifundamental ${\bf 3}^*$ of color $SU(3)$ of QCD i.e. single quark of three colors and a single antiquark of 3 anticolors, nine states are obtained. ...
Solidification's user avatar
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Color vectors for antiquarks

For a single quark, the colour vectors are given by $$r=\begin{pmatrix} 1 \\ 0 \\0 \end{pmatrix} \qquad g=\begin{pmatrix} 0 \\ 1 \\ 0 \end{pmatrix} \qquad b=\begin{pmatrix} 0 \\ 0 \\ 1 \end{pmatrix}$$ ...
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Can black holes have colour charge? [duplicate]

Does the no hair's theorem take into account all the elementary particles and forces, and in particular can a black hole have color charge?
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Why $\pi^+$ meson possible combinations of quarks is only three?

I am a starter at nuclear and particles physics. I am reading particles and nuclei an introduction to the physical concepts. There was a paragraph about Colour-neutral particles and how only ...
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What happens inside a proton?

This post contains 3 questions but they are very similar. I saw from this question What's inside a proton? and other websites that protons aren't really made up of three quarks, but a lot of ...
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„Orbital“ of an quark

Inspired by the idea of the electron orbitals ( probability of finding an electron in an atom) i was wondering what that would look like inside a proton or neutron for quarks. For simplicity consider ...
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Can we detect and measure color charge?

I was listening to the "Why This Universe" podcast about dark matter and Dr. Dan Hooper mentioned briefly that electric and color charge can be readily detected. Can color charge be ...
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How can I describe, in QFT, Weyl spinors coupled to a strong version of the gluon gauge field?

Let's assume a massless Weyl-spinor field. My aim is to let them interact by a gluon-like gauge-field, which has a bigger much bigger coupling, color charge, than the standard color interaction. This ...
MatterGauge's user avatar
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Is the concept of bicolored gluons mathematically precise/meaningful? Please explain

Each flavour of quark carries a colour quantum number: red, green or blue. I know what it means mathematically. But elementary textbooks (e.g, particle physics by Griffiths) also say that gluons are ...
Solidification's user avatar
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Quantum chromodynamics - why are there no $rrb$ or $ggr$ terms?

$$\Psi_{colour}^{qqq} = \frac{1}{\sqrt{6}}(rgb + gbr + brg -grb - rbg - bgr)$$ My lecturer stated that there cannot be any $rrb$ or $ggr$ terms in the expression above. I would like to understand what ...
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If a spin singlet cannot change, how can it interact with electromagnetism?

Let's say there's a Hydrogen atom in a spin triplet state. $$ | \downarrow\downarrow \rangle$$ Now let's say a photon with spin 1 came along abs was absorbed by the atom. We don't know if the proton ...
Fernando Franco Félix's user avatar
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A gluon can have nine independent, bicolored states. How are some of the additions of these individual states, like $r\bar{r}+g\bar{g}+b\bar{b}$?

This came from the 25th page of the following pdf: http://www.gammaexplorer.com/wp-content/uploads/2014/03/Quarks-and-Leptons-An-Introductory-Course-in-Modern-Particle-Physics.pdf Sorry if I am asking ...
Coopthecomposer's user avatar
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Fundamental reason for the color and flavor group to be the same?

The answer to this question might just be a straight-up "no, it's just a coincidence", but since coincidences are rarely a thing in physics, I thought I'd ask. Is there a fundamental reason ...
Mauro Giliberti's user avatar
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What is "the famous 3R experiment" for quark colours?

This page says: "The famous $3R$ experiment also suggests that whatever force binds the quarks together has 3 types of charge (called the 3 colors)." Google seems to think that the $3R$ ...
AirOfMystery's user avatar
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Is it possible for an isolated quark to exist if it's bound to one or more non-virtual gluons to render the system color neutral?

We know color-neutral bound systems of quarks exist in the form of hadrons, we suspect color-neutral bound systems of gluons exist in the form of glueballs, we have a candidate particle which may be ...
Adam Lincoln Steele's user avatar
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What units is strong nuclear charge measured in? [duplicate]

Do particles have a strong nuclear charge in the same way as they have electric charge? If so what unit would be used to measure this? Would it be measured in Coulomb for instance?
Derek Seabrooke's user avatar
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Can a complex wave function just be seen as two real functions describing a particle and antiparticle state? [duplicate]

Let's assume electromagnetism. There are two charges. The wave function is complex but can be seen canonically as a vector in $\mathbb{R}^2$. Can we see one of the components as the electron and the ...
NicAG's user avatar
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Is there a relationship between the properties of different charges of a fundamental particle?

To begin with, I'm a high school student and so my understanding of QFT is quite basic. Due to this, I'd prefer a simple answer (it would be great if it's yes/no) along with a very basic explanation. ...
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How is the colour quantum number not conserved in this process?

I stumbled upon this CERN article, where I found this diagram describing the process $gg \rightarrow HH$: I'm still new to QCD, and I don't see how a coloured gluon can decay into colourless final ...
Physicist_285's user avatar
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Feriz rearrangement

For a tetraquark system $QQ\bar{Q}\bar{Q}$, with diquark-antiquark configuration, the color configuration can be $|6_{QQ}\otimes \bar{6}_{\bar{Q}\bar{Q}}\rangle_{1}$ or $|\bar{3}_{QQ}\otimes 3_{\bar{Q}...
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Why are electric charge, color charge referred to "quantum numbers"?

Quantum numbers characterizing a state are eigenvalues of operators. This is what we learn in quantum mechanics. But in quantum gauge theories, the electric charge, color charge, etc are also referred ...
Solidification's user avatar
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Pentaquark color structure [closed]

I just heard about pentaquarks. How do you assign color charge to a pentaquark like duuc anti c
Phy's user avatar
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Why is the $SU(4)$ group not suitable for describing color symmetry?

How to demonstrate that the $SU(4)$ group cannot be a group of symmetry of a color charge?
Lord_of_Physics's user avatar
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Do hadrons have color moments?

Hadrons have electrical moments since they are made up of both positive and negative charges. Water molecules have dipole moments for the same reason even though they are electrically neutral. Since ...
Jason's user avatar
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What does "singlet state" mean in the context of colour charge, and do red, green and blue colours cancel?

I find myself very confused by the usage of spin terminology to other quantum numbers. A singlet state is the only spinless state of the system. Now, if we consider the possible colour states $|r\...
Pancake_Senpai's user avatar
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Can mesons be in $b \overline{b}$, $r \overline{r}$, $g \overline{g}$ states?

Can a meson be in a pure $b \overline{b}$, $r \overline{r}$, $g \overline{g}$ state or does it have to be in the $\frac{1}{\sqrt{3}}\left(b \overline{b}+r \overline{r}+g \overline{g}\right)$ state? ...
Quanta's user avatar
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Interchanging positions of Gell-Mann matrices with Dirac matrices, Pauli matrices

The anti-commutation relations for Gamma matrices $\big\{\gamma ^\mu , \gamma ^\nu \big\} = 2g ^{\mu \nu} $ can be used for interchanging positions of the respective matrices in a given expression, ...
user263315's user avatar
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Can indistinguishable particle wavefunctions be written as a product of total observable eigenstates?

Consider the wavefunction of say two electrons in an external potential, associated with two possible states $\phi_a$ and $\phi_b$. Furthermore, each electron can have two spin states $\chi_1$ and $\...
user2224350's user avatar
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Eight gluons, what are the properties of two of them?

If there are 8 gluons, and 6 of them can be represented as a color/anticolor pair (red/antiblue for example), that leaves 2 "other" gluons. How do these two gluons differ from each other? ...
Madman's user avatar
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Bern-Carrasco-Johansson (BCJ) Double Copy and Color-Kinematic duality

According to the wikipedia page on Strong Gravity, the theory is considered "non-mainstream", but from what I can gather there have been some very interesting progress and results since it ...
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What is a "multicharge nuclei"?

When doing some reading on particle physics, I came across the concept of a "multicharge nuclei". A Google search of this phrase returns a number of research papers, but no definition for what a "...
The Pointer's user avatar
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What is the colour factor, when calculating width for Tau decay?

I am trying to answer a question that asks to find the branching fraction of $\tau^{+}$ decays. In the answers, it gives that the widths are as follows: $$\Gamma(\tau^- \rightarrow ν_{\tau} d \...
Xenophilius's user avatar
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Understanding the proof of the "Photon-Decoupling Identity" for colour-ordered Yang-Mills amplitudes

Problem: To prove the Photon-Decoupling Identity for colour-ordered Yang-Mills amplitudes: $$0= A(1,2,3,...,n)+A(2,1,3,...,n)+...+A(2,3,...,1,n) \tag{1}$$ I know I must use $(2)$, which expresses ...
user7077252's user avatar
2 votes
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Colour-ordering formula of QCD amplitudes (tree-level)

I have been studying colour-ordered amplitudes and spinor helicity formalism for a while. It is now apparent to me that I do not fully understand the 'master' formula which allows us to relate the ...
dzejkob's user avatar
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Why there is no such a thing as colour moment?

I was busy google about different types of electric and magnetic dipole moment then a thought suddenly striked me, why there is no colour multipole moment?
user6760's user avatar
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If quarks change colours constantly how are proton and neutron stable relatively?

Say for example a proton is composed of Up, Up and Down (valance) quarks and suppose the Down quark absorbs a gluon, Down quark must change colour in order to conserve colour charges but so must the ...
user6760's user avatar
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What do we mean by charge in physics?

I am drawing the comparison between electrical charge and colour charge, in electric charges they communicate with (virtual) photon and photon itself is a boson carrying no charge. How about colour ...
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What's the definition of $\bar\psi$ in QCD?

This is a two part question. What is the definition of $\bar\psi$ in QCD? In QED I know that $\bar\psi=\psi^\dagger\gamma^0$, but in QCD we also have flavor and/or color space. In particular, I'm ...
WillG's user avatar
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What is the magnetic-equivalent field of moving quark color charge?

A moving electric charge induces a magnetic field. What kind of field is induced by a moving (quark) color-charge? Are there 3 kinds of color-magnetic fields? How would they interact with color-...
JohnDeeDoe's user avatar
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Does quarks always pulls each other?

Pions consist of quark and antiquark and strong force keeps them together. So color charge and anticolor charge attracts each other. But in proton we have 3 quarks and they also attract each other. It ...
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