A New State of Matter between the Hadronic Phase and the Quark-Gluon Plasma?

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Hauptverfasser: Fujimoto, Yuki, Fukushima, Kenji, Hidaka, Yoshimasa, McLerran, Larry
Format: Preprint
Veröffentlicht: 2025
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author Fujimoto, Yuki
Fukushima, Kenji
Hidaka, Yoshimasa
McLerran, Larry
author_facet Fujimoto, Yuki
Fukushima, Kenji
Hidaka, Yoshimasa
McLerran, Larry
contents Lattice-QCD simulations and theoretical arguments hint at the existence of an intermediate phase of strongly interacting matter between a confined hadron gas and a deconfined Quark-Gluon Plasma (QGP). We qualitatively and semi-quantitatively explore and differentiate the phase structures in the temperature window from the QCD pseudo-critical temperature $T_c\simeq 160\;\text{MeV}$ to the pure-gluonic deconfinement temperature $T_d\simeq 285\;\text{MeV}$. We propose a three-regime picture using a hadron resonance gas (HRG) description augmented with the glueball spectrum based on the analysis of a large number, $N_c$, of colors. We estimate the entropy density from our model to confirm that the lattice-QCD data are bracketed with three regimes, i.e., a hadron gas, a QGP, and a new phase for $T_c \lesssim T \lesssim T_d$. In this new phase that we name a Spaghetti of Quarks with Glueballs (SQGB), thermal degrees of freedom of quarks are deconfined, yet gluons remain confined in glueballs. Since the Hagedorn temperature, $T_H\sim 285\;\text{MeV}$, is universal in the meson and the glueball sectors, in the infinite $N_c$ limit, the phase diagram in the plane of the baryon chemical potential and the temperature is reduced to the one with the confined and deconfined phases and Quarkyonic Matter at high density. At large but finite $N_c$, an SQGB window may open between these phases. We point out that the SQGB has interesting similarities with Quarkyonic Matter and that this matter in the large $N_c$ limit is confined as measured by the interaction between heavy quarks, but behaves in other respects like a quasi-free gas of quarks. As a result of the extrapolation to $N_c=3$, we present a revised phase diagram with the SQGB phase bounded by thermal crossovers. Finally, we give a quantitative analysis of chiral symmetry restoration in the SQGB phase.
format Preprint
id arxiv_https___arxiv_org_abs_2506_00237
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle A New State of Matter between the Hadronic Phase and the Quark-Gluon Plasma?
Fujimoto, Yuki
Fukushima, Kenji
Hidaka, Yoshimasa
McLerran, Larry
High Energy Physics - Phenomenology
High Energy Physics - Lattice
Nuclear Theory
Lattice-QCD simulations and theoretical arguments hint at the existence of an intermediate phase of strongly interacting matter between a confined hadron gas and a deconfined Quark-Gluon Plasma (QGP). We qualitatively and semi-quantitatively explore and differentiate the phase structures in the temperature window from the QCD pseudo-critical temperature $T_c\simeq 160\;\text{MeV}$ to the pure-gluonic deconfinement temperature $T_d\simeq 285\;\text{MeV}$. We propose a three-regime picture using a hadron resonance gas (HRG) description augmented with the glueball spectrum based on the analysis of a large number, $N_c$, of colors. We estimate the entropy density from our model to confirm that the lattice-QCD data are bracketed with three regimes, i.e., a hadron gas, a QGP, and a new phase for $T_c \lesssim T \lesssim T_d$. In this new phase that we name a Spaghetti of Quarks with Glueballs (SQGB), thermal degrees of freedom of quarks are deconfined, yet gluons remain confined in glueballs. Since the Hagedorn temperature, $T_H\sim 285\;\text{MeV}$, is universal in the meson and the glueball sectors, in the infinite $N_c$ limit, the phase diagram in the plane of the baryon chemical potential and the temperature is reduced to the one with the confined and deconfined phases and Quarkyonic Matter at high density. At large but finite $N_c$, an SQGB window may open between these phases. We point out that the SQGB has interesting similarities with Quarkyonic Matter and that this matter in the large $N_c$ limit is confined as measured by the interaction between heavy quarks, but behaves in other respects like a quasi-free gas of quarks. As a result of the extrapolation to $N_c=3$, we present a revised phase diagram with the SQGB phase bounded by thermal crossovers. Finally, we give a quantitative analysis of chiral symmetry restoration in the SQGB phase.
title A New State of Matter between the Hadronic Phase and the Quark-Gluon Plasma?
topic High Energy Physics - Phenomenology
High Energy Physics - Lattice
Nuclear Theory
url https://arxiv.org/abs/2506.00237