Abstract
The approach to the eta'-eta 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 U_A(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 U_A(1) transition, with smooth and gradual melting of anomalous mass contributions. This way we obtain a substantial drop of the eta' mass around the chiral transition temperature, but no eta mass drop. This is consistent with the present empirical evidence.
Highlights
The experiments at heavy-ion collider facilities—such as RHIC, LHC, FAIR, and NICA—aim to produce a new form of hot and/or dense QCD matter [1,2]
Clear signatures of its production are very much needed. The most compelling such signal would be a change in the pertinent symmetries, i.e., the restoration of the symmetries of the QCD Lagrangian which are broken in the vacuum, notably the [SUAðNfÞ flavor] chiral symmetry for Nf 1⁄4 3 1⁄4 2 þ 1 light quark flavors q, and the UAð1Þ symmetry
We have studied the temperature dependence of the masses in the η0 − η complex in the regime of the crossover restoration of chiral and UAð1Þ symmetry
Summary
The experiments at heavy-ion collider facilities—such as RHIC, LHC, FAIR, and NICA—aim to produce a new form of hot and/or dense QCD matter [1,2]. Clear signatures of its production are very much needed The most compelling such signal would be a change in the pertinent symmetries, i.e., the restoration (in hot and/or dense matter) of the symmetries of the QCD Lagrangian which are broken in the vacuum, notably the [SUAðNfÞ flavor] chiral symmetry for Nf 1⁄4 3 1⁄4 2 þ 1 light quark flavors q, and the UAð1Þ symmetry. This provides much motivation to establish that experiment shows this, as well as to give theoretical explanations of such phenomena.
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