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A solution to the U(3) ×{} U(3) problem---the absence of a ninth pseudoscalar Goldstone boson---is proposed. The mechanism for eliminating the unwanted Goldstone boson involves the same infrared instabilities of Yang-Mills theory which confine quarks and eliminate physical "color" states. A formal argument is presented, and two models of quark confinement illustrate the mechanism involved in eliminating the spurious massless state.
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Kogut et al. (1974) studied this question.
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