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We study U₀ (1) symmetry and its relation to chiral symmetry at finite temperature through the application of the functional renormalization group to the SU (3) quark-meson model. Very different from the mass gap and mixing angel between and ^' mesons, which are defined at the mean-field level and behavior like condensates, the topological susceptibility includes a fluctuation-induced part which becomes dominant at high temperature. As a result, the U₀ (1) symmetry is still considerably broken in the chiral symmetry restoration phase.
Jiang et al. (Wed,) studied this question.