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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1answer
492 views

How to determine Gauge Boson charge?

Given the field strength: $$F^a_{\mu\nu} = \partial_\mu A^a_\nu - \partial_\nu A^a_\mu + g \; f^{abc} A^b_\mu A^c_\nu$$ We'd get interactions between three and four bosons, former one will look like:...
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Could we draw field lines for colour charge?

Electromagnetic charge can be represented with field lines. These are pleasingly intuitive and can be used to visualise Gauss's Law and Maxwell's Laws. Later on Gauss and Maxwell get rolled into a ...
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1answer
164 views

Quark colour charge at gluon emission/absorption

Suppose I have a very simple QCD diagram, where a quark emits a gluon and continues on. Can I describe such process through "usual" quantum mechanics? More specifically, can I use the concept of ...
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1answer
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In nonabelian gauge theory, does the ordinary or covariant derivative go into the statement of current conservation?

Before equation (77.35), Srednicki's QFT book says We define the chiral gauge current $j^{a\mu}$ [where $a$ is a color index]. Its covariant divergence (which should be zero, according to Noether's ...
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3answers
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How (or when) do gluons change the color of a quark?

I know a baryon is only stable when it contains a quark of each color. And as far as I know, the gluon essentially changes the color of a quark and moves onto the next, and this is what holds the ...
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1answer
376 views

What exactly is the color charge in QCD? [duplicate]

I don't have strong background in particle physics. Though, I had learnt a little of it. I have gone through the basic of these stuffs (pretty OK). If I have done my homework right, color charge (R,G,...
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1answer
330 views

What is the effect of the Gell-Mann matrices on color antiparticles?

I'm studying QCD and I can't understand how exactly are defined the color antiparticles. Indeed, we have the particle color triplet $(r,g,b)$. With the usual SU(3) algebra, we define the 8 Gell-Mann ...
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1answer
233 views

Color confinement and integer electric charge?

Quarks have electric charges proportional to one third of the elementary electric charge, but both mesons and baryons have integer electric charge. Is there some deep explanation from a more ...
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704 views

Why are 3 colors used in QCD?

The mapping of strong charge to RGB left me believing that there are only 3 conserved quantities in QCD. I recently came to the understanding that there are in fact 8 conserved quantities, as ...
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3answers
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What's the difference between Quark Colors and Quark Flavours?

Each of the six "flavors" of quarks can have three different "colors". The quark forces are attractive only in "colorless" combinations of three quarks (baryons), quark-antiquark pairs (mesons) and ...
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1answer
289 views

$SU(3)$ global gauge group

Referring to the quantum observables of quarks, is it true that the color $SU(3)$ unitary representation commutes with all observables? I am not referring here to the local $SU(3)$ gauge theory, I ...
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3answers
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How many kinds of “weak charges” exist?

For electricity, we have one charge, for the strong force three. How many are there connected to the weak force? Three, because of the W- and Z-particles? For the weak force, there is the isospin, ...
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3answers
638 views

How does quark color affect the identity of a hadron?

I've read about colors relating to quarks and hadrons and I know that they can change colors because of the exchange with gluons, but does changing color change the type of hadron? Does a proton ...
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2answers
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Why does confinement apply only to quarks, and not to nucleons?

When energy is input in an attempt to break quark bonds one simply generates more quarks through hadronisation. The explanation my physics book gives for this is that "the strength of the strong ...
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1answer
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How emerges a color “magnetic” (chromomagnetic) field?

How does the color charge of quarks brings a "color magnetic (chromomagnetic) field" into existence? When the quark is moving you should expect that it causes a field just as a magnetic ...
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332 views

Can quarks have anti-colors? [closed]

What is the reason that the color properties we call red, green and blue have become tied to quarks, while what we call anti-red, anti-green and anti-blue has become tied to anti-quarks? Do note that ...
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1answer
292 views

Up/Down Quark Color and Isospin

I'm reading some notes that say the reason that the strong interaction conserve isospin is because the up and down quarks have the same color... but I'm not very convinced. Is this a universal truth? ...
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1answer
181 views

How many glueballs are there?

As I understand there are eight types of gluons (linear combinations of color/anticolor pairs with varying amplitudes) which can combine (for very short periods) to form glueballs. If there were no ...
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1answer
183 views

A few questions on quarks, gluons and the strong force

I wanted to answer for myself some pretty fundamental questions pertaining to the strong interaction, color charge and quarks, but I'm sort of stumbling on a few. So I wanted to find the reason/...
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Do quark charges repel one another?

Positive electrical charges repel other positive charges, and negatives repel negatives. But does that happen for quarks, too? I never saw mention of it, but if so, that would mean the up quarks in a ...
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1answer
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The charges of the forces

I am trying to establish a simplified understanding of the fundamental forces to explain them to a young audience. If we say that gravity has one charge (attractive), electromagnetism has two charges ...
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1answer
268 views

Why do we say that gluons carry color charge?

We know that gluons are Lie algebra $su(3)$-valued one-form fiels $A_{\mu}$. And because of $[A_\mu,A_\nu]$ does not vanish generally for the non-Abelian case, gluons have self-interactions. Now how ...
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1answer
520 views

Why there aren't gluons with charges like $b b$ or $r r$?

So my principal question is the one in the object above. But then I have another question related. Supposing I have a $bg$ gluon. How may I write it in the octet basis? Thank you for your help!!
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1answer
996 views

Colorless charge in a baryon

In a baryon there are 3 quarks and in a meson there are one quark + one anti-quark. So color charge is colorless ( a color singlet state ) in a meson. But how is it colorless in a baryon?
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Why doesn't the color force between two quarks have an inverse square law?

From what I understand the color force between two quarks doesn't decrease with distance. Why is it that the color force doesn't decrease with the square of the distance if there are three dimensions ...
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Can non-color-neutral nucleons exist?

In a proton or neutron, one quark is red, another blue, and the last green, making it color neutral. Is it possible for a nucleon to consist of colors rgg, rbb, rrb, etc? If three quarks of such color ...
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1answer
137 views

QCD Color Structure relation [closed]

i want to proof the following relation : \begin{equation} t^a t^b \otimes t^a t^b = \frac{2}{N_C} \delta^{ab} \mathbb{1} \otimes \mathbb{1} - \frac{1}{N_C} t^a \otimes t^a \end{equation} Right now I ...
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Why is $U(1)$ special when defining global charges?

For gauge groups like $SU(2)$ and $SU(3)$ etc. we know that observable states such as mesons or baryons must be charge neutral. However, for a $U(1)$ gauge group we can have charged initial states in ...
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1answer
723 views

Permissible combinations of colour states for gluons

My lecturer has said that there are 8 types of gluons (I'm assuming that the repetition of $r\bar{b}$ is a typo that is meant to be $r\bar{g}$) $$r\bar{b}, b\bar{r}, r\bar{g}, g\bar{r}, g\bar{b}, b\...
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1answer
784 views

Is color charge a quantum mechanical observable?

If I had 2 pions that were identical, except one was comprised of a red and anti-red, and the other was comprised of a green and anti-green, would I be able to perform an experiment that distinguishes ...
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1answer
291 views

how can a particle can have a spin of 2 [duplicate]

i have seen some analogies of spin using playing cards but i am struggling to grasp the concept due to this making no sense in terms of playing cards
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1answer
425 views

Colour decomposition in QCD

I am looking to compute the matrix element for the process gg -> u ubar at leading order. It is straightforward to calculate the non-colour part of the usual s, t and u channels. I will call these ...
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1answer
422 views

What does the mass of a quark mean?

The mass of an electron includes the mass of the electric field it creates. If electrons have a radius, it's known to be small enough that the mass of the electric field would be more than the total ...
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1answer
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Why does sea colour differ from place to place?

If you notice the colour of sea changes from place to place. At some places it is of blue or green and even different in beach. What must be the reason?
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Measure of interaction of two quarks and Casimir operators [closed]

Let's have two quarks, which refers to representations of $r_{1}$ and $r_{2}$ of color symmetry group. They create bounded state which refers to the representation $r$. There is a statement that ...
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1answer
445 views

Group theoretical reason that Gluons carry color-charge and anti-colorcharge

I was wondering how it is possible to see from the $SU(3)$ Gauge Theory alone that Gluons carry two charges colors: $g\overline{b}$ etc. Some background: The W-Bosons (pre-symmetry breaking) ...
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How can a detector distinguish between a photon and a gluon

Considering that both gluons and photons have no mass, no charge and spin 1, I was wondering how one can tell the difference, if they hit a detector after a collision at the LHC. I know that gluons ...
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1answer
380 views

Could the universe have non-vanishing net colour charge?

I've heard that the strong force doesn't decrease in strength with increasing distance, and that's why quarks must be confined within hadrons. But could there be, say, a single quark out there, so ...
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3answers
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Color-charge conservation in proton decay

In some extensions of the Standard Model of particle physics (Supersymmetry with R-parity violation being a prominent example), the proton is allowed to decay, e.g. via $p\to e^+\pi^0$: While this ...
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How can opaque black object occur?

I know the fact that a material appeared as black when all wavelength photons were absorbed. I also know that opaque object is the result of reflection and scattering of light wave. Is it right? ...
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1answer
190 views

Color factor for squark-quark-antiquark vertex

I am trying to do a tree level calculation of cross section in a process that involves sbottom exchange. There is a $ \widetilde{b} q \bar{q} $ vertex, where $q$ and $\bar q$ are quark and anti-quark ...
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Why there are no $uuu$ and $ddd$ baryons with spin 1/2?

What is preventing $Δ^{++}$ and $Δ^-$ spin 3/2 baryons from going to a lower-energy state with spin 1/2 similar to that of protons and neutrons? I don't think the Pauli exclusion principle can ...
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1answer
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How to sum over final, and average over initial color states?

Consider the $s$-channel mediated top quark production process $$ d + \overline d \rightarrow t + \overline t$$ Using the Feynman rules for QCD, the amplitude contains a color factor $$[c^\dagger _{\...
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1answer
202 views

Are mesons color polarized?

The binding of quarks in mesons baffles me. It's an Occam's Razor thing. Since a meson is a colorless, the simplest way to bind its two quarks together is to use a $U(1)$ Cartan subalgebra of $SU(3)$. ...
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1answer
135 views

What will happpen between a proton and an anti-neutron with unmatched color charges?

Maybe a stupid question because my search didn't return anything. Assuming in low energy state, a proton (made by a red up, a blue up and green down quarks) meets an anti-neutron (made by an anti-...
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463 views

Base quantities and charges

Is there an unit of color charge? I haven't found it, so I suppose that it doesn't exist, if this is right, why? Isn't it supposed that every measurable quantity can be expressed in terms of base ...
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Why is color conserved in QCD?

According to Noether's theorem, global invariance under $SU(N)$ leads to $N^2-1$ conserved charges. But in QCD gluons are not conserved; color is. There are N colors, not $N^2-1$ colors. Am I ...
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What IS Color Charge?

This question has been asked twice already, with very detailed answers. After reading those answers, I am left with one more question: what is color charge? It has nothing to do with colored light, ...
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1answer
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Which pion is mediator in nucleon-nucleon interaction

In nucleon-nucleon interactions of n-n, p-p, n-p how do you determine which pion is the mediator?
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Does the color of a quark matter in a meson?

QCD and confinement specify that hadrons must be color-neutral. My understanding is that this means you can have mesons (quark + antiquark) or baryons with 3 quarks, one of each color: Red+green+blue=...