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I think that we may add that in the confining phase, the QCD-string descritpion of quarks (say, mesons, which are bound states of quark/anti quarks) is that these particles sit at endpoints of "QCD-strings" (I use "" to distinguish this from the normal superstring which is a well defined object, though it failed for the moment at describing exactly ...

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Quarks as we know them are fundamental particles, which means that they do not have smaller constituents. This however does not imply that they cannot decay. A particle in quantum field theory does not need to have constituents to decay into, it can in principle decay into any particle its corresponding field couples to (interacts with), as long as it obeys ...

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The $u$ & $d$ quarks decay into $d$ & $u$ quarks and bosons (e.g., W bosons)--this is effectively what happens to the hadrons in weak interactions. This (incomplete) chart shows, for instance, $$u\to d+W^+\\ d\to u+W^-$$ There isn't anything sub-quark, as far as the standard model goes.

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The current understanding of quarks is, that they are a fundamental particle. This means for the energy scales currently available in particle accelerators all quarks have behaved like point-like particles. Due to the strange nature of the color-field (the energy stored in it increases with distance instead of decreasing) if you break a proton apart (which ...

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Consider an UHECR neutron approaching a magnetar. The Lorentz force acting on the quarks will soon exceed the QCD string tension, at that point quark anti-quark pairs get created giving rise to pions. These pions in turn get polarized and you get more pions. So, you basically get a chain reaction yielding more and more pions until the speed of the pions ...

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Statements like "The mass of the electron includes the mass of the electric field it generates" have to be taken veeery carefully. In quantum field theory we can calculate the backreaction of the electric field our electron creates on itself, which is the mass shift I think you talk about. For these calculations to make sense, we need to make use of ...

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You got that the wrong way around. Hadrons are made up of quarks. There are different types of hadrons, e.g. baryons (3 quarks) and mesons (1 quark, 1 antiquark). So a proton is just one special type of baryon and therefore also a hadron. Now what quarks are made up of is not a sensible question in the frame we use to think about particle physics nowadays. ...

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