Questions tagged [color-charge]

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

Filter by
Sorted by
Tagged with
4 votes
3 answers
1k views

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 ...
user avatar
0 votes
2 answers
72 views

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 ...
user avatar
  • 13
0 votes
2 answers
179 views

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 ...
user avatar
0 votes
0 answers
18 views

Reflection identity for color ordered gluon partial amplitudes

I'm currently studying various modern methods for calculating scattering amlpitudes, and I'm following Dixon's notes on the topic: https://arxiv.org/abs/hep-ph/9601359. When talking about the color ...
user avatar
  • 180
-1 votes
1 answer
71 views

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 ...
user avatar
8 votes
3 answers
481 views

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 ...
user avatar
2 votes
1 answer
98 views

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 $3R$ ...
user avatar
9 votes
3 answers
1k views

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 ...
user avatar
1 vote
1 answer
68 views

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?
user avatar
3 votes
2 answers
302 views

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 ...
user avatar
  • 446
2 votes
2 answers
84 views

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. ...
user avatar
  • 23
2 votes
1 answer
76 views

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 ...
user avatar
2 votes
0 answers
29 views

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}...
user avatar
0 votes
1 answer
57 views

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 ...
user avatar
0 votes
1 answer
69 views

Pentaquark color structure [closed]

I just heard about pentaquarks. How do you assign color charge to a pentaquark like duuc anti c
user avatar
  • 13
2 votes
1 answer
103 views

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?
user avatar
1 vote
0 answers
45 views

What experimental evidence is there for quarks constantly changing colors?

In other words, why is it believed that the quarks are constantly changing colors? This question answers why theoretically but I'm curious what experimental observation prompted this theoretical piece ...
user avatar
  • 579
5 votes
3 answers
197 views

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 ...
user avatar
  • 579
2 votes
1 answer
381 views

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\...
user avatar
2 votes
2 answers
158 views

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? ...
user avatar
  • 503
1 vote
1 answer
224 views

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, ...
user avatar
-2 votes
2 answers
138 views

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 $\...
user avatar
1 vote
2 answers
212 views

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? ...
user avatar
  • 31
2 votes
0 answers
132 views

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 ...
user avatar
  • 14k
1 vote
1 answer
37 views

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 "...
user avatar
0 votes
2 answers
167 views

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 \...
user avatar
4 votes
1 answer
214 views

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 ...
user avatar
1 vote
0 answers
245 views

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 ...
user avatar
  • 145
0 votes
0 answers
67 views

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?
user avatar
  • 11.4k
3 votes
1 answer
130 views

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 ...
user avatar
  • 11.4k
2 votes
2 answers
96 views

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 ...
user avatar
  • 11.4k
1 vote
1 answer
153 views

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 ...
user avatar
  • 3,060
0 votes
1 answer
43 views

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-...
user avatar
0 votes
2 answers
246 views

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 ...
user avatar
3 votes
1 answer
281 views

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 ...
user avatar
  • 351
2 votes
2 answers
785 views

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{...
user avatar
1 vote
0 answers
59 views

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 ...
user avatar
  • 141
0 votes
1 answer
299 views

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 ...
user avatar
  • 3,443
1 vote
2 answers
267 views

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, ...
user avatar
5 votes
1 answer
126 views

Would Color Confinement apply in higher dimensions?

As I understand it color confinement comes from the fact that as the distance between two color charges increases the color potential energy increases, instead of decreasing, and the energy needed to ...
user avatar
0 votes
1 answer
170 views

What is the systematic way to determine the spin of lowest-lying states of baryons like $uuu$, $ssd$, $uds$ etc?

I learned that for the lowest lying states, $uuu$, $sss$, $ddd$ can only have $J=\frac{3}{2}$ $uus$, $ddu$, $ddu$, $ssu$ etc can only have $J=\frac{1}{2},\frac{3}{2}$ $uds$ can have $J=\frac{1}{2}, \...
user avatar
  • 3,803
1 vote
1 answer
177 views

Is there a physical difference between the colors of quarks?

Is there any physical difference to the way, say, red quarks behave compared to green or blue ones? Or is it just an intrinsic property that they have that doesn't provide any physical difference ...
user avatar
0 votes
3 answers
984 views

Why do quarks and gluons have colour?

I asked a question here a few days ago and got some fantastic answers so I'm going to continue. Let me preface this by saying I know quarks do not actually have 'colour', but colour is some sort of ...
user avatar
  • 191
1 vote
1 answer
107 views

A fundamental question about charge and speed of a particle [duplicate]

Hi everybody and happy 2019. In my teaching sessions sometimes someone asks questions i cannot truly answer (although i have many arguments on it) and here's one that really puzzles me: A massless (...
user avatar
3 votes
0 answers
47 views

How many antiquarks can be squeezed inside a nucleon without upsetting exclusion principle?

I read about a nucleon with 3 Strange quarks which clearly violates PEP, however this was soon resolved by introducing colour charges. Then I read about colour confinement where surplus energy can be ...
user avatar
  • 11.4k
0 votes
1 answer
85 views

Where do the color indices come back in $SU(3)$ Yang-Mills Quantization?

Can the partition function of $SU(3)$ (the Generic Partition function for a yang-mills theory found on the linked wiki page below), be split into a sum of 8 functional integrals for each gauge field? ...
user avatar
  • 877
3 votes
0 answers
128 views

How do we show that gluon-fields have color?

I understand how to derive the QCD lagrangian based on certain assumptions about Quark fields and $SU(3)$ gauge invariance and in the final expression one finds the term $(A_µ)^c*T_c$ where $T_c$ is ...
user avatar
  • 877
0 votes
1 answer
71 views

Coefficients of Color Potential in Quarks [duplicate]

I was wondering if there was a relation between the fractional coefficients $$2/3, 1/3$$ obtained when calculating color potential for quarks and the value of electric charge for the up and down quark....
user avatar
2 votes
2 answers
110 views

Do color changing interactions between up and down quark exist?

In our Standard Model course we wrote down the term for the quark-gluon interaction of the left handed $SU(2)_L$ quark doublet $q_L$ as: $\mathscr{L} = … + \bar{q}_L \gamma^\mu iG^a_\mu(x) \lambda^a ...
user avatar
0 votes
1 answer
173 views

Difference between boundedness (electrons around nuclei) and color confinement (quarks)

I have read these questions: How does the orbiting of electrons around nuclei START? Bound electrons don't move, right? Do different orbitals overlap in multielectron atom? What is the difference ...
user avatar