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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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 ...
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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 ...
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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 ...
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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. ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 ...
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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 $3R$ ...
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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 ...
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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?
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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 ...
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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 ...
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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 ...
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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
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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?
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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 ...
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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\...
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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?
...
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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, ...
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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 $\...
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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? ...
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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 "...
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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:
$$\Gamma(\tau^- \rightarrow ν_{\tau} d \...
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Understanding the proof of the "Photon-Decoupling Identity" for colour-ordered Yang-Mills amplitudes
Problem:
To prove the Photon-Decoupling Identity for colour-ordered Yang-Mills amplitudes:
$$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 ...
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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 ...
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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?
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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 ...
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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 ...
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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-...
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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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How are quarks assigned color charge?
As always, I'll preface that I am wildly undereducated, so i may be overlooking something or be completely unaware of another relevant property.
Color Confinement dictates that to "assemble" a baryon ...
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Confusions with gluons. How many of them are there?
Gluons are bicolored objects. They are made out of one color and one anticolor. Therefore, there seems to be nine possible states $r\bar{r},r\bar{b},r\bar{g},b\bar{r},b\bar{b},b\bar{g},g\bar{r},g\bar{...
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Why use $SU(3)$ and not $SL(3, \mathbb{R})$ for color charge? [duplicate]
Why do we use the group $SU(3)$ and not $SL(3, \mathbb{R})$ for color charge?
As far as I can tell, the $SL(3, \mathbb{R})$ is volume and orientation preserving, by the fact that it has unit ...
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Why don't green and anti-green gluons immediately annihilate each other?
I can't believe I haven't found an answer elsewhere.....
I have read repeatedly about blue/anti-blue gluons, etc., but no reason as to why they don't destroy each other immediately.....
Or maybe they ...
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Color symmetries in variant QCD
Suppose we only have two colors, for example, red (R) and blue (B) to construct the wave functions of baryons and mesons and that the color symmetry is SU (2) and not SU (3). In this situation, ...
