"Color embeddings, charge assignments, and proton stability" in Reviews of Modern Physics.

Gell-Mann, Murray. P. Ramond, and R. Slansky. "Color embeddings, charge assignments, and proton stability" in Reviews of Modern Physics, October 1974, vol 50 no. 4. Original wrappers. The Gell-Mann et al is on pp 721-744 in the issue of pp 721-915. G/VG copy. "Three problems in hypothetical unified theories of electromagnetic, weak, and strong interactions are discussed here. First, the problem of embedding color in any simple gauge group is solved, and a complete classification of theories where the fermion color is restricted to 1c, 3c, and ¯3c of SUc3 is given. Generalizations are also indicated. Second, an unbroken U1 generated by electric charge is embedded into each of the above theories and the charge assignments analyzed. Third, the general problem of stabilizing the proton by a suitable atomic mass number A is studied for the same set of theories. It is always possible to define A if the gauge group is not too small.--abstract.