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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77 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?
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Color function for tetraquark

The color function for tetraquark configuration $(qq)(\bar{q}\bar{q})$ is shown following: $$ \zeta_1=\frac{1}{2\sqrt6}[(rb+br)(\bar{b}\bar{r}+\bar{r}\bar{b})+(gr+rg)(\bar{g}\bar{r}+\bar{r}\bar{g})+(...
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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 ...
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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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47 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\...
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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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102 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? ...
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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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Proving the BCJ relation

Background I am aware that the colour ordered amplitudes are cyclically symmetric, for example, for a 4 point amplitude: $$A_4(1,2,3,4)= A_4(2,3,4,1) \tag{1}$$ Problem I am trying to prove the BCJ ...
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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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1answer
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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, ...
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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 ...
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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}, \...
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120 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 ...
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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 ...
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1answer
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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 (...
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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 ...
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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? ...
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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 ...
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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....
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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 ...
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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 ...
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Colors sensitivity by human eye and light wavelength [duplicate]

I do not understand why human eye sees different colours from the LED TV/screen. Especially violet. For example, how we get yellow color on TV. There are 3 small diodes Red, Green Blue in LED screen ...
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What keeps quarks separate (strong force pulls, but what repels to equal out)

We know that the strong force keeps quarks together, that is mediated by gluons (and their charge is called color charge). We know that the residual strong force keeps neutrons and protons together in ...
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From Reflection Spectrum to Preceived Color

I have a reflection curve over the visible spectrum (350nm to 700nm) of a sample. Now, I am interested to know what preceived color one would see ? Is it possible to go from the reflection spectrum ...
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“Color charge” of the adjoint fermion?

What kind of "color charge" does the adjoint fermion carry? Let us consider the SU(N) gauge theory. The gauge field is in the adjoint representation (rep). Well-Konwn: If the fermion is in SU(N) ...
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Can the three quark colors be considered to correspond to different particles?

Is it harmless to count three, say, up quark particles instead of one up quark with three colors, as well as 8 different gluons instead of one with different color?
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Quark-Gluon color relationship in pure QCD

Consider pure QCD, flavor turned off. There are 3 quarks and 3 anti-quarks given by the fundamental IRR of SU(3) and its conjugate rep. We associate the three colors and anti-colors with the three ...
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The “Big Rip” -vs- Color confinement [closed]

One model for the end of the Universe says that space will continue to expand faster and faster, until even atoms are ripped apart in the so called big Rip. It is also stated by QCD (quantum ...
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Understanding mathematical explanation for Chudakov Effect

I'm trying to better understand some properties of QCD and currently I'm looking into understanding color coherence. I've got the book "Elementary Particle Physics: Foundations of the Standard Model, ...
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How would an interaction with a single charge, and a charged weightless carrying particle behave?

We learnt about, among the other three fundamental interactions, the strong interaction. The particles that are affected by it are those with color-charge. It's carrying particles, gluons, have a ...
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Is it possible different coloured quarks have slightly different masses?

For example, could the red-down-quark have a slightly different mass to the red-up-quark? Since quarks rest masses are so much lighter than the particles they make up, that little bit of different ...
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Why does the $\Lambda^0$ exist?

In looking at the particle charts I see 3 Sigma baryons with very similar masses and other similar properties, which makes sense since they all have one strange quark plus two others from the (up,down)...
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$SU(3)$ Color Symmetry

I have following (maybe a bit general) question about the $SU(3)$-symmetry of color by quarks: If I consider the analogy to the $SU(2)$-symmetry of isospin $I$ crucially it concers the conservation ...
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Quark jet color

When a 2-jet event occurs due to a quark + antiquark emerging back-to-back, the jets ultimately decay to stable particles. Each jet starts with a quark (or antiquark) carrying a color and ends as a ...