On the origin of the $$N_c^1$$ scaling in the confined but chirally symmetric phase at high T
Year: 2025
Type: article
Abstract: There is lattice evidence that the QCD matter above the chiral restoration temperature $$T_{ch}$$ T ch and below the deconfinement temperature $$T_d$$ T d , called stringy fluid, is characterized by approximate chiral spin symmetry, which is a symmetry of confinement in QCD with light quarks. The energy density, pressure and entropy density in the stringy fluid scale as $$N_c^1$$ N c 1 , which is in contrast to the $$N_c^0$$ N c 0 scaling in the hadron gas and to the $$N_c^2$$ N c 2 scaling in the quark-gluon plasma. Here we clarify the origin of the $$N_c^1$$ N c 1 scaling. We employ a solvable field-theoretical large $$N_c$$ N c chirally symmetric and confining model. In vacuum the confining potential induces a spontaneous breaking of chiral symmetry. The mesons are spatially localized states of quarks and antiquarks. Still in the confining regime the system undergoes the chiral restoration phase transition at $$T_{ch}$$ T ch because of Paili blocking of the quark levels required for the existence of the quark condensate, by the thermal excitation of quarks and antiquarks. The same Paili blocking leads to a delocalization of the color singlet low-spin meson-like states that become infinitely large in the chiral limit. Consequently the stringy fluid represents a very dense medium of the overlapping huge color-singlet low-spin quark-antiquark systems. The Bethe–Salpeter equation that determines the rest-frame excitation energies of the color-singlet quark-antiquark system is $$N_c$$ N c -independent both in vacuum and in the medium in the confining regime. The excitation energy of the quark-antiquark color-singlet systems scales as $$N_c^0$$ N c 0 , i.e. as meson mass in vacuum. The $$N_c^1$$ N c 1 scaling of the energy density in the stringy fluid is provided by the fluctuations of the color-singlet quark-antiquark systems.
Source: The European Physical Journal C
Author: L. Ya. Glozman
Institution: University of Graz
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: diamond
Funder: Austrian Science Fund
OpenAlex ID: W4416664941