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1

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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Why have our eyes not evolved to see “gluons”? Because gluons are virtual particles rather than real particles. See the Wikipedia article: "Although in the normal phase of QCD single gluons may not travel freely, it is predicted that there exist hadrons that are formed entirely of gluons — called glueballs. There are also conjectures about other ...


0

To put it simply, there is an evolutionary advantage to be able to see the objects around you using photons, but there would be no particular survival advantage to be able to see gluons, even if they weren't essentially confined to the nucleus.


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Short answer: because the Sun emits photons, not gluons. Having a long range sense is vital for finding food and recognizing predators. Seeing light and forming an image of our surroundings is one of the three long range senses we have (the others are hearing and smelling). Gluons are extremely short range; they don't even exist as naked particles. How ...


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In short, the answer is: because gluons behave in a way that makes them useless for this purpose. To understand why, let's back up a little and look at how photons are useful, and then see how gluons behave differently. We (animals pretty broadly) evolved to see photons because they allow us to move around in and respond to our environment more ...


0

I cannot give you an advice on how to do this computation by hand in the most efficient way, but if you need a way to cross-check what you have obtained so far and you have access to Mathematica, you could use FeynCalc for that. The calculation of the $gg \to q \bar{q}$ matrix element squared (unpolarized) is shipped with FeynCalc as an example (see here) ...



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