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Nobel prize to A. Salam awarded in 1979. Co-winners S. L. Glashow and S. Weinberg "for their contribution to the theory of the unified weak and electromagnetic interaction between elementary particles, including, inter alia, the prediction of the weak neutral current''

SALAM 1964

Salam, A.; Ward, J.C.;
Electromagnetic and Weak interactions
Phys. Lett. 13 (1964) 168;

Reprinted in
Selected papers of Abdus Salam, editor A. Ali et al., p. 210-213..
Gauge theory of weak and electromagnetic interactions, eidtor C. H. Lai, p. 181-184..

Motivation
One of the recurrent dreams in elementary particles physics is that of a possible fundamental synthesis between electromagnetism and weak interactions. The idea has its origin in the following shared characteristics:
1) Both forces affect equally all forms of matter-leptons as well as hadrons.
2) Both are vector in character.
3) Both (individually) possess universal coupling strengths. Since universality and vector character are features of a gauge-theory these shared characteristics suggest that weak forces just like the electromagnetic forces arise from a gauge principle.
There of course also are profound differences:
1) Electromagnetic coupling strength is vastly different from the weak. Quantitatively one may state it thus: if weak forces are assumed to have been mediated by intermediate bosons (W), the boson mass would have to equal 137 M_p, in order that the (dimensionless) weak coupling constant g_W²/4 equals e²/4
In the sequel we assume just this. For the outrageous mass value itself (M_W approx 137M_p) we can offer no explanation. We seek however for a synthesis in terms of a group structure such that the remaining differences, viz:
2) Contrasting space-time behaviour (V for electromagnetic versus V and A for weak).
3) And contrasting S and I behaviours both appear as aspects of the same fundamental symmetry. Naturally for hadrons at least the group structure must be compatible with SU(3).
.

Related references
More (earlier) information appears in
A. Salam and J. C. Ward, Nuovo Cim. 11 (1959) 568;
See also
S. L. Glashow, Nucl. Phys. 10 (1959) 107;
J. Schwinger, Ann.Phys. 2 (1957) 407;
M. Gell-Mann, Phys. Rev. 125 (1962) 1067;
Y. Ne'eman, Nuovo Cim. 27 (1963) 567;
Y. Nambu and P. G. O. Freund, Phys. Rev. Lett. 12 (1964) 714;
M. Gell-Mann, Phys. Lett. 12 (1964) 63;
A. Salam and J. C. Ward, Nuovo Cim. 27 (1961) 922;
R. Gatto, Nuovo Cim. 28 (1963) 567;