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The parton model assumes that nucleons are composed of three valence quarks that share the momentum of the nucleon in an approximately equitative way. That means that the valence quark pdf's have a peak around $x = 1/3$, and have much lower values at $x \to 0$ and $x \to 1$. In addition to that, you have interactions between quarks (nowadays we know that ...

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1) Note that the non-relativistic gluon model of glueballs has even less justification than the non-relativistic quark model of baryons and mesons. This is because the model messes up the spin assignments: Massless gluons have only two spin states, but non-relativistic gluons have three. 2) The color quantum numbers are trivial: The product  [8]\times ...

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PQCD is only applicable at really high energy and FAIR CBM experiment will have quite low energy and finite baryonic density. As it is said on the official doc : http://www.fair-center.eu/fileadmin/fair/publications_FAIR/FAIR_BTR_3a.pdf Low energy model will be available to compare data, but in my opinion, lattice QCD is the best tool available to discuss ...

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Well, in the NJL model you get rid of the gluon. They are considered to be frozen in the low energy limit where you are working because the mass is higher than the energy. Thus you are only working with quarks, and you consider interaction between quarks via effective coupling constants. But in the standard model, gluons (seem to) acquire an effective mass ...

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At lowest order, color screening comes from virtual quark/antiquark pairs, just like charge screening comes from electron/positron pairs in QCD. The diagram/effect is also referred to as 'vacuum polarization' and is shown below. Charge antiscreening comes from virtual gluon pairs; its diagram is below.

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You are asking four questions, whose answers are routinely provided in textbooks. We consider it in QCD since there is no fundamental reason to exclude it, and topological configurations such as instantons, etc.. might well generate it in an effective low energy theory: the rule of thumb is that anything that is not prohibited has to emerge out of the ...

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