Abstract
We study the mean-field thermodynamics and the characteristics of the net-baryon number fluctuations at the phase boundaries for the chiral and deconfinement transitions in the Hybrid Quark-Meson-Nucleon model. The chiral dynamics is described in the linear sigma model, whereas the quark confinement is manipulated by a medium-dependent modification of the particle distribution functions, where an additional scalar field is introduced. At low temperature and finite baryon density, the model predicts a first-, second-order chiral phase transition, or a crossover, depending on the expectation value of the scalar field, and a first-order deconfinement phase transition. We focus on the influence of the confinement over higher-order cumulants of the net-baryon number density. We find that whereas the cumulants show a substantial enhancement around the chiral phase transition, they are not as sensitive to the deconfinement transition.
Highlights
Exploration of the phase diagram of quantum chromodynamics (QCD), the theory of the strong interaction, at finite temperature and density is one of the most challenging topics in high-energy particle and nuclear physics
II, we introduce the parity doublet model at finite density and finite temperature, as well as its extension – the Hybrid QuarkMeson-Nucleon model – that includes the mechanism to mimic quark confinement
At low T and μB, the quark degrees of freedom are suppressed, while the nucleons get suppressed at high T and μB. This characteristic behavior is associated with the deconfinement transition, which is a crucial feature of the model [21]
Summary
Exploration of the phase diagram of quantum chromodynamics (QCD), the theory of the strong interaction, at finite temperature and density is one of the most challenging topics in high-energy particle and nuclear physics. The masses of the positive-parity groundstates are found to be rather insensitive to temperature, while the masses of negative-parity states drop substantially with increasing temperature, and the parity doublers become almost degenerate with a finite mass in the vicinity of the chiral crossover Tc. Despite unphysically heavy pion mass used in the study, this is likely an imprint of the chiral symmetry restoration in the baryonic sector of QCD, and is expected to occur in cold dense matter. The model includes quark degrees of freedom on top of hadrons, but prevents the quarks from their unphysical onset at low density This can be achieved by a new auxiliary scalar field to which the fermions are coupled non-trivially.
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