Isospin nucleon doublet

A similar mechanism can be invoked to give mass to the quarks [though there may be other sources of mass for the quarks (see Section 20.3)], but this would leave the up-type quarks, the analogues of the neutrinos, massless. In order to construct an interaction invariant under weak SU(2) and weak U 1) which will give mass to the quarks with = 1/2, it turns out, on the basis of Table 9.2, that we need a Higgs doublet with Yw = —1-Recall that = has Y y = 1, and is a weak isospin doublet. Recall also, that for ordinary isospin, the nucleon doublet N = ( ) and the antinucleon doublet N = (jp) (note the minus sign ) transform identically under isospin rotations. By analogy... 

For an additional degree of freedom of a particle that defines one of the two possible states in which it exists, we shall apply now the concept of isospin (in analogy with the theory of the nucleus where the isospin doublet includes protons and neutrons, which are treated as two states of the same particle - the nucleon [122]). For a pair of states (a,/ ) we introduce the isospin operators... 

If we group p and n into an isospin doublet N = ( ) then for the nucleons... 

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See also in sourсe #XX -- [ ]

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