# 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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### 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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### 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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### 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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### 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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### 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....