QCD thermodynamics through the crossover as a gas of confining strings with repulsive interactions

Abstract

We investigate QCD thermodynamics in the intermediate-temperature regime using a gas of confining strings supplemented by excluded volume (EV) corrections. In this description, the discrete hadron resonance spectrum is replaced by an exponentially growing open-string spectrum characterized by a Hagedorn temperature $T_H$, related to the confining string tension. With a common EV parameter shared by mesons and baryons, the model gives a good description of bulk lattice-QCD thermodynamics above the pseudocritical temperature. Among the values considered, $T_H\simeq 300\text{MeV}$ provides the best agreement, lower than the value $T_H\simeq 320-340\text{MeV}$ inferred from ideal-string-gas fits to the vacuum hadron spectrum. A simultaneous calibration of the mesonic and baryonic EV parameters gives $b_M\simeq 0.19{\text{fm}}^3$ and $b_B\simeq 0.73{\text{fm}}^3$. Within the present spectral ansatz, the larger baryonic EV parameter indicates that stronger effective suppression is required in the baryon sector, although noticeable tensions remain in several conserved-charge observables.

Comments: 12 pages, 6 figures