Abstract
Historically, quantum chromodynamics (QCD) originated as a development of the quark model. In the early sixties it was established that hadrons could be classified according to the representations of what today we would call flavour SU F (3) (Gell-Mann, 1961; N’eman, 1961). This classification presented a number of features that are worth noting. First of all, only a few, very specific representations occurred; they were such that they built representations of a group SU(6) (Gürsey and Radicati, 1964; Pais, 1964) obtained by adjoining the group of spin rotations SU(2) to the internal symmetry group, SU F (3) .However, neither for SU F(3), or SU(6) did the fundamental representations (3 and 3 for SUF (3)) appear to be realized in nature. This led Gell-Mann (1964a) and Zweig (1964) to postulate that physical hadrons are composite objects, made up of three quarks (baryons) or a quark—antiquark pair (mesons). These three quarks are now widely known as the three flavours, u (up), d (down) and s (strange); the first two carry the quantum numbers of isospin, and the third strangeness. It has been found that precisely those representations of SU F (3) occur that may be obtained by reducing the products 3 × 3 × 3 (baryons) or 3 × 3(mesons); when the spin ½ of the quarks is taken into account, the SU(6) scheme is obtained.
Anaximander, student of Thales of Miletus, maintained that the primordial substance of things should be called the unbound: he was the first to use this word for the substratum. He pointed out, however, that this primeval substance, of which all elements in heaven and the worlds are made, is not water or any of the so-called “elements” we find around, but a different, limitless substance which fills all of them.
Anaximander, 546 B.C.E.
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References
In fact, a colour quantum number was first introduced by Han and Nambu (1965).
See Bardeen, Fritzsch and Gell-Mann (1972); Fritzsch and Gell-Mann (1972); Fritzsch, Gell-Mann and Leutwyler (1973).
See Epstein, Glaser and Martin (1969) and Bogolubov, Logunov and Todorov (1975), from where one can trace the relevant literature.
For example, in standard textbooks such as Bogoliubov and Shirkov (1959); Bjorken and Drell (1965) or Itzykson and Zuber (1980).
Functional derivatives are defined in Appendix H.
We place carets over operators temporarily.
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© 1999 Springer-Verlag Berlin Heidelberg
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Ynduráin, F.J. (1999). Generalities. In: The Theory of Quark and Gluon Interactions. Texts and Monographs in Physics. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-662-03932-8_1
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DOI: https://doi.org/10.1007/978-3-662-03932-8_1
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