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We are players in a theory theater. A play we show here is the 't Hooft mechanism: if a gauge symmetry and a global symmetry are broken by one complex scalar field by the Higgs mechanism then there survives a global symmetry below the breaking scale. In the string compactification, it is realized when an anomalous gauge U(1) symmetry is created. This is a good example of obtaining a global PQ symmetry at an intermediate scale, realizing an ``invisible'' axion with mass around $10^{-4}$ eV for a cold dark matter candidate.

Anomalous gauge-U(1), ’t Hooft mechanism, and “invisible” QCD axion from string