Why fluctuations of conserved charges in the confining regime above $T_{\mathrm{ch}}$ behave as if the quarks were free?

Authors

L Ya Glozman

Published in

The European physical journal. C, Particles and fields. Volume 86. Issue 10. Pages 1223. Epub Oct 23, 2026.

Abstract

Some cumulants of the fluctuations of conserved charges soon above the chiral crossover behave as if the quarks were free. This was taken by many as evidence of deconfinement. At the same temperatures the mesonic correlators reveal the chiral spin and SU(4) symmetries, indicating that the propagating degrees of freedom are massless quarks connected into color singlets by the chromoelectric confining string. These correlators are qualitatively different from the free quark gas. Here we clarify the reason for the difference. The conserved quark number densities do not propagate in time but do propagate in spatial directions. The mesonic propagators calculated in full QCD differ radically from the free quark loop (quark gas) above $T_{\mathrm{ch}}.$ In contrast, the quark number density spatial propagator in full QCD at $T\ge 220$  MeV is very close to the free quark loop. In other words, the conserved charges do not see confinement, in contrast to the mesonic correlators. This is consistent with the well understood quark-hadron duality at $T=0$ in $e^{+}{e}^{-}\to hadrons,$ where at invariant masses above 2 GeV the cross-section in the confining regime is represented by the free quark loop plus small perturbative corrections. All these features above $T_{\mathrm{ch}}$ but below the deconfinement temperature $T_d$ can be combined within the following microscopic picture of the stringy fluid matter. It is a medium of the overlapping strongly interacting color singlet clusters. The quark interchanges between the clusters, required by Pauli principle, make the quarks quasifree, which is reflected in fluctuations of conserved charges.

PMID:
42927002
Bibliographic data and abstract were imported from PubMed on 25 Oct 2026.

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