ONLY three quark colors (and three anti-colors)?

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  • #1
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Main Question or Discussion Point

I realize that because of the Pauli exclusion principle, two identical quarks (such as two up quarks in a proton) cannot occupy the same space, hence the variations in color provided by qluon interaction.

I have two questions:

Can "color" be thought of as a state, such a light switch can be on or off? And thus, there is no physical difference between a red, green, or blue quark (I realize those terms are allegorical), because the "red" one and instant later will be the "green" one, etc.

The next question is this: Must there only be three colors of quarks (and three anti-colors)? Does the Standard Model PROHIBIT more than three colors? Or is it that only three colors are necessary and that there is only evidence of thre colors so far?

Thanks
 

Answers and Replies

  • #2
SpectraCat
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I realize that because of the Pauli exclusion principle, two identical quarks (such as two up quarks in a proton) cannot occupy the same space, hence the variations in color provided by qluon interaction.

I have two questions:

Can "color" be thought of as a state, such a light switch can be on or off? And thus, there is no physical difference between a red, green, or blue quark (I realize those terms are allegorical), because the "red" one and instant later will be the "green" one, etc.

The next question is this: Must there only be three colors of quarks (and three anti-colors)? Does the Standard Model PROHIBIT more than three colors? Or is it that only three colors are necessary and that there is only evidence of thre colors so far?

Thanks
I am getting out of my area of expertise here, but I believe the answer to your question is that, according to the standard model and the theory of quantum chromodynamics, there are EXACTLY 3 colors (and their corresponding anti-colors). This is because the theory of color charge was developed to explain the observed experimental results, which suggested an underlying fundamental symmetry that transformed as the SU(3) group. (For reference, spin transforms as SU(2) group, as does isospin, which is another property of nucleons.)

Thus, I *THINK* the answer is that, if experiments suggested there was another kind of color charge, it would mean that the Standard Model was in serious trouble ....
 
  • #3
Bill_K
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You mentioned one reason - color is necessary to properly fit three quarks having Fermi-Dirac statistics together to form a nucleon. Another reason is the anomaly cancellation, which for consistency requires the sum of charges of the particles in a fermion generation to be zero. This only works if the quarks are counted with a weighting factor of 3 because they are really three different particles:

3(2/3) + 3(-1/3) + (-1) + 0 = 0.
 
  • #4
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The next question is this: Must there only be three colors of quarks (and three anti-colors)? Does the Standard Model PROHIBIT more than three colors? Or is it that only three colors are necessary and that there is only evidence of thre colors so far?
Yes, the Standard Model prohibits the existence of more than 3 colors. Prohibits by definition, since it explicitly states that that there are 3 of them, period.

However, there are extensions of Standard Model that assume more than 3 colors and these are called "technicolor" models.
 
  • #5
tom.stoer
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There are two different perspectives:

First there is a pure algebraic perspective where one attributes spin, color and flavor (up, down, strange, ...) to a quark.

Later one discovered QCD which adds a dynamical perspecive where gluons couple to a color-current density just like photons couple to electric-current density.
 
  • #6
Bill_K
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However, there are extensions of Standard Model that assume more than 3 colors and these are called "technicolor" models
The technicolor in technicolor models are not "more colors", they're an entirely new quantum number characterizing an entirely new force.
 
  • #7
tom.stoer
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exactly, technicolor means essentially

spin, color (rgb) and flavor (up, down, strange, ...), technicolor (...)
 

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