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η′ and η mesons at high T when the U_A(1) and chiral symmetry breaking are tied

The approach to the η′−η complex employing chirally well-behaved quark-antiquark bound states and incorporating the non-Abelian axial anomaly of QCD through the generalization of the Witten-Veneziano relation is extended to finite temperatures. Employing the chiral condensate has led to a sharp chiral and UA(1) symmetry restoration, but with the condensates of quarks with realistic explicit chiral symmetry breaking— which exhibit a smooth, crossover chiral symmetry restoration in qualitative agreement with lattice QCD results—we get a crossover UA(1) transition with a smooth and gradual melting of anomalous mass contributions. In this way, we obtain a substantial decrease in the η′ mass around the chiral transition temperature, but no decrease in the η mass. This is consistent with current empirical evidence.

nonperturbative ; QCD ; anomaly ; U_A(1) symmetry ; bound states

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