Free The Higgs Boson: Searching for the God Particle by Scientific American Editors Page B

renormalization studies that had been developed by Veltman.
    Formally the results were encouraging,
but if the theory was to be a realistic one, some means had to be found to confine the Yang-Mills fields to a finite range. I had just learned at a summer school how Kurt Symanzik of the German Electron Synchrotron and Benjamin W. Lee of the Fermi National Accelerator Laboratory had successfully hand led the renormalization of a theoretical model in which a global symmetry is spontaneously broken. It therefore seemed natural to try the Higgs mechanism in the Yang-Mills theory, where the broken symmetry is a local one.
    A few simple models gave encouraging results: in these selected instances all infinities canceled no matter how many gauge particles were exchanged and no matter how many loops were included in the Feynman diagrams. The decisive test would come when the theory was checked by the comp uter program for infinities in all possible diagrams with two loops. The results of that test were available by July, 1971; the output of the program was an uninterrupted string of zeros. Every infinity canceled exactly.
Subsequent checks showed that infinities were also absent even in extremely complicated Feynman diagrams. My results were soon confirmed by others,
notably by Lee and by Jean Zinn-Justin of the Saclay Nuclear Research Center near Paris.
    The Yang-Mills theory had begun as a model of the strong interactions, but by the time it had been renormalized interest in it centered on applications to the weak interactions. In 1967 Steven Weinberg of Harvard University and independently
(but later) Salam and John C. Ward of Johns Hopkins University had proposed a model of the weak interactions based on a version of the Yang-Mills theory in which the gauge quanta take on mass through the Higgs mechanism.
They speculated that it might be possible to renormalize the theory, but they did not demonstrate it. Their ideas therefore joined many other untested conjectures until some four years later,
when my own results showed it was just that subclass of Yang-Mills theories incorporating the Higgs mechanism that can be renormalized.
    The most conspicuous trait of the weak force is its short range: it has a significant influence only to a distance of 10 -15 centimeter, or roughly a hundredth the radius of a proton. The force is weak largely because its range is so short: particles are unlikely to approach each other closely enough to interact.
The short range implies that the virtual particles exchanged in weak interactions must be very massive. Present estimates run to between 80 and 100 times the mass of the proton.
    The Weinberg-Salam-Ward model actually embraces both the weak force and electromagnetism. The conjecture on which the model is ultimately founded is a postulate of local invariance with respect to isotopic spin; in order to preserve that invariance four photon-like fields are introduced, rather than the three of the original Yang-Mills theory.
The fourth photon could be identified with some primordial form of electromagnetism.
It corresponds to a separate force, which had to be added to the theory without explanation. For this reason the model should not be called a unified field theory. The forces remain distinct;
it is their intertwining that makes the model so peculiar.
    At the outset all four of the fields in the Weinberg-Salam-Ward model are of infinite range and therefore must be conveyed by massless quanta; one field carries a negative electric charge, one carries a positive charge and the other two fields are neutral. The spontaneous symmetry breaking introduces four Higgs fields, each field represented by a scalar particle. Three of the Higgs fields are swallowed by Yang-Mills particles, so that both of the charged Yang-Mills particles and one of the ne utral ones take on a large mass. These particles are collectively named massive intermediate vector bosons, and they are designated W+, W- and Z 0 . The fourth