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I About Quarks

  1. Dec 19, 2017 #41
    It seems to me that if you go around talking about electrons, positrons, and photons, before talking about propagation in the EM field, then for the same reason you should be just as able to talk about quarks and gluons. Are electrons and positron just for popular discussion?
  2. Dec 19, 2017 #42


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    How did you get that from what I said?
  3. Dec 19, 2017 #43
    It sounds like we are avoiding talking about the ontology of unobservables, again, because quarks and gluons are not directly observable, though electrons and positrons are observable. Tell me, do we have just as much trouble talking about the properties of W-, W+, and Z0 boson? For those aren't directly observable either as I recall, since their half-life is 3*10-25s.
  4. Dec 19, 2017 #44


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    If you read what I said instead of what you wanted to read I think you would learn more. You have not addressed what I asked you in the slightest. I am done with this thread.
  5. Dec 19, 2017 #45
    I'm sorry, but it's frustrating to hear that quarks have certain properties on the one hand, and then hear that they don't on the other.
  6. Dec 19, 2017 #46
    SU(3) gauge symmetry of quarks says that you can look at them as having r,g,b charges; _and also_, you can look at them as having charges in any other valid basis of "color space".

    Same goes for gluons.

    For quarks, "r,g,b basis" looks easy and natural.

    Gluons don't have a "nice looking" basis. Sorry. Complain to the gods of group theory.
  7. Dec 19, 2017 #47
    I appreciate your efforts. So I'm looking for how gluons interact with quarks. I've seen a basis showing a combination of color and anticolor for each gluon. And I'm trying to visualize which gluons interact with which quarks. I've been told that a quark of a particular color can change that color by emitting a gluon. And likewise they can change their color by absorbing a gluon. But the labels I've seen so far on the gluons suggest that they interact with quarks of a certain color. So instead of every gluon interacting with every quark, the labeling suggest that there are restrictions on the kinds of interaction. Is there a simple list or table stating, for example, that this gluon interacts with these quarks an no others, etc? Thanks.
  8. Dec 19, 2017 #48
    This is a _layman_ description. Because layman wouldn't understand gauge invariance.

    Technically speaking, there are no "quarks with a particular color". Color's value is not a gauge-invariant concept: gauge invariance, by definition, is the freedom to arbitrarily change quark and gluon field values (by multiplying them by suitable 3x3 complex matrix), this can be done _locally_ (the matrix can vary from point to point!), and this change will not be physically observable.

    IOW: you can repaint any quark however you want, including any complex superposition of colors (as long as they add up to 1).

    Since there are no "quarks with a particular color", you don't have to limit yourself to imagining only quarks with a particular color, and to gluons with only a pair of color-anticolor. Color superpositions are _fine too_.
  9. Dec 20, 2017 #49
    OK I can accept that. It's like expressing a wave function in various basis but the operator math is still the same.

    But still, somewhere in the math they came up with a specific number of quarks and a specific number of gluons that transcends color labels. Does this math also specify the number of ways these gluons interact with these quarks? Does every gluon interact with every quark? Or, perhaps, does each gluon only interact with two quarks?
  10. Dec 20, 2017 #50
    I think not. (That was probably a stupid question.) For if that were the case, then it would be impossible to enumerate various kinds of gluons. They would be indistinguishable. In fact, aren't the gluons specifically distinguished from each other by the fact that they interact with quarks differently?
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