Gluon spin and quark confinement

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Discussion Overview

The discussion revolves around the properties of gluons, quarks, and the nature of the strong force, particularly in the context of quark confinement in hadrons. Participants explore the implications of color charge in mesons and baryons, and the dynamics of quark interactions under Quantum Chromodynamics (QCD).

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant asserts that gluons, being spin 1 particles, can create both attractive and repulsive forces, questioning whether the confinement force between quarks in mesons is always attractive due to their opposite color charges.
  • Another participant emphasizes the complexity of hadrons, noting that while valence quarks are significant, the overall dynamics of QCD must also be considered, suggesting an effective attraction among valence quarks.
  • A participant seeks clarification on the combination of color charges, specifically whether "blue+red" indeed results in "anti-green," indicating a potential misunderstanding or nuance in the description of color combinations.
  • One participant discusses the static quark approximation used in lattice QCD, suggesting that while it simplifies the confinement mechanism, it does not capture the full dynamics of QCD, yet may still provide reasonable insights into valence quark interactions.
  • Another participant agrees that the reasoning based on color-anticolor configurations leading to an attractive force is valid, while also reiterating the importance of understanding the context of valence quarks in baryons.

Areas of Agreement / Disagreement

Participants express varying views on the nature of forces between quarks, with some agreeing on the attractive nature of the confinement force while others highlight the complexity and potential for both attractive and repulsive interactions. The discussion remains unresolved regarding the exact dynamics of quark interactions in different configurations.

Contextual Notes

Participants acknowledge limitations in their reasoning, particularly regarding the assumptions made in the static quark approximation and the complexities of QCD that may not be fully addressed in their discussions.

joly
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Gluons are spin 1 particles so the Strong Force can both attract and repulse. The constituent partons of a meson are a quark and an antiquark so they must carry a given color and its anticolor, respectively, in order that there is no net color carried by the parton. In that case, the force between the quark and antiquark must be always attractive since it involves opposite type of charges. Is that reasoning correct?

If so, how does this work for a baryon, which contains 3 constituent quarks of 3 different colors? Could we have both attractive and repulsive components in the (overall attractive) confinement force, or is QCD also always attractive in that case?
 
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Hadrons are not as easy as N quarks sitting around. The valence quarks are important, but the whole QCD mess is important as well.

The valence quarks in a hadron feel an effective attraction to the other two valence quarks as well. "Blue+red" combined is very similar to "anti-green", for example. But don't take that too literally.
 
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mfb said:
"Blue+red" combined is very similar to "anti-green"

Doesn't blue+red combined exactly give anti-green? (I'm asking this because you wrote similar)
 
Thank you. I was thinking of the heavy (static) quark, quenched, approximation that is e.g. studied by lattice QCD. This is a simple case to picture the confinement mechanism, although as you say it does not contains the full story: the QCD string appears to break down when light quark pair-creation is allowed. Nevertheless, it seems educative to consider the static quenched approximation even if it is not fully QCD. In that case, I suppose that the valence quark picture should be reasonable. If so, does the reasoning based on the color-anticolor configuration of the q-qbar pair leading to an always attractive force makes sense?

For the baryons, blue+red=anti-green seems to be a good answer. It reminds of the quark-diquark picture.
 
Garlic said:
Doesn't blue+red combined exactly give anti-green? (I'm asking this because you wrote similar)
If you add the colors, yes, but you have two different valence quarks with those colors, not a single anti-green valence quark.
joly said:
If so, does the reasoning based on the color-anticolor configuration of the q-qbar pair leading to an always attractive force makes sense?
Yes.
 
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