# Tag Info

4

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 ...

-5

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.

2

You now want to go back to position space. I'll do that here very schematically which gives the answer without keeping track of the overall factor. Essentially, under the Fourier transform, $q_{i\mu} \to \partial_\mu$ and $\epsilon_{i\mu} \to A_\mu$. Then  g^2 \text{Tr}(T^aT^b) \varepsilon_{\mu\nu\rho\sigma} q_1^\mu q_2^\nu \epsilon_1^\rho ...

0

The beta function is scheme dependent beyond two loops. I suspect that it should be possible to devise a scheme (which is useless in practice) in which all coefficients of the beta function vanish beyond two loops. In supersymmetric gauge theories without matter the exact perturbative beta function was determined by NSVZ, ...

2

I don't think that this is right. The leading operator is the OPE of the nucleon currents is the chiral condensate, see Belyaev and Ioffe (1982), http://inspirehep.net/record/178457?ln=en.

2

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 ...

63

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) ...

0

You already do this to some extent when your power supply is an electrolyte-based battery (a, b) --- there you have motion of both negative and positive ions in the electrolyte. Electrons are free to move in conductors when the Fermi energy falls within a band of energy levels rather than in a gap when there are no allowed energies. However, the band/gap ...

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