# Tagged Questions

The charge of the strong nuclear force is called "color".

3k views

### Mathematically, what is color charge?

A similar question was asked here, but the answer didn't address the following, at least not in a way that I could understand. Electric charge is simple - it's just a real scalar quantity. Ignoring ...
2k views

### 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 ...
219 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 ...
2k views

### 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, ...
3k views

### What is the definition of colour (the quantum state)?

I heard somewhere that quarks have a property called 'colour' - what does this mean?
715 views

### 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 ...
790 views

### Is there an explanation for the 3:2:1 ratio between the electron, up and down quark electric charges?

I understand that the NNG formula relates $Q$, $I_3$, and $Y$ and can be derived in QCD; does this unambiguously predict the electric charge ratios without making assumptions about the definitions of ...
550 views

442 views

### 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?
70 views

### 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 ...
91 views

### 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 ...
187 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 ...
212 views

### 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 ...
75 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 ...
105 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!!
106 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 ...
44 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 ...
210 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) ...
66 views

### QCD Color Structure relation [closed]

i want to proof the following relation : $$t^a t^b \otimes t^a t^b = \frac{2}{N_C} \delta^{ab} \mathbb{1} \otimes \mathbb{1} - \frac{1}{N_C} t^a \otimes t^a$$ Right now I ...
36 views

### 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 ...
130 views

### 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?
76 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 ...
52 views

### 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 ...
133 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 ...
20 views

### Why are quarks and gluons confined [duplicate]

I understand that quarks and gluons are confined to the particle they are part of but why is this? It seems that the color force is the only force that causes confinement so what is different about ...
38 views

### 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 ...
84 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 ...
730 views

### 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? ...
107 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 ...
89 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-...
63 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/...
51 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 ...