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Register a new userMagnetized QCD phase diagram: net-baryon susceptibilities
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Pedro Fernando Simoes Costa
Publication date
2018
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English
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Employing the Polyakov extended Nambu-Jona-Lasinio model, we determine the net-baryon number fluctuations of magnetized three-flavor quark matter. We show that the magnetic field changes the nature of the strange quark transition from crossover to first-order at low temperatures. In fact, the strange quark undergoes multiple first-order phase transitions and several critical end points emerge in the phase diagram.
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The net-baryon number fluctuations for three-flavor quark matter are computed within the Polyakov extended Nambu$-$Jona-Lasinio model. Two models with vanishing and nonvanishing vector interactions are considered. While the former predicts a critical end point (CEP) in the phase diagram, the latter predicts no CEP. We show that the nonmonotonic behavior of the susceptibilities in the phase diagram is still present even in the absence of a CEP. Therefore, from the nonmonotonic behavior of the susceptibilities solely, one cannot assume the existence of a CEP. We analyze other possible properties that may distinguish the two scenarios, and determine the behavior of the net-baryon number fluctuations and the velocity of sound along several isentropes, with moderate and small values. It is shown that the value of the susceptibilities ratios and the velocity of sound at two or three isentropic lines could possibly allow to distinguish both scenarios, a phase diagram with or without CEP. Smoother behaviors of these quantities may indicate the nonexistence of a CEP. We also discuss the critical behavior of the strange sector.
The kurtosis and skewness of net baryon-number fluctuations are studied for the magnetized phase diagram of three-flavor quark matter within the Polyakov extended Nambu$-$Jona-Lasinio model. Two models with magnetic catalysis and inverse magnetic catalysis are considered. Special attention is given to their behavior in the neighborhood of the light and strange critical end points (CEPs). Several isentropic trajectories that come close the CEPs are studied in order to analyze possible signatures of a CEP in the presence of external magnetic fields. The effect of the magnetic field on the velocity of sound, $v_s^2$, when both the light and strange CEPs are approached from the crossover region is also investigated by calculating their temperature and baryon chemical potential dependencies at fixed distances from these CEPs. Regions with large fluctuations but no CEP in nonmagnetized matter develop a CEP under the action of a strong magnetic field. Besides, the Landau quantization of the quark trajectories may result in the appearance of extra CEPs, in particular, in the strange sector for strong magnetic fields, identifiable by the net baryon-number fluctuations. Stiffer (smoother) fluctuations in the region of the CEP are characteristic of models that do not predict (do predict) the inverse magnetic catalysis at zero chemical potential. Particularly interesting is the ratio $chi^4_B/chi^2_B$ that has a more pronounced peak structure, indicating that it is eventually a more convenient probe for the search of a CEP. The speed of sound shows a much richer structure in magnetized quark matter and allows one to identify both chiral and deconfinement transitions.
The phase structure of two-flavor QCD is explored for thermal systems with finite baryon- and isospin-chemical potentials, mu_B and mu_{iso}, by using the Polyakov-loop extended Nambu--Jona-Lasinio (PNJL) model. The PNJL model with the scalar-type eight-quark interaction can reproduce lattice QCD data at not only mu_{iso}=mu_B=0 but also mu_{iso}>0 and mu_B=0. In the mu_{iso}-mu_{B}-T space, where T is temperature, the critical endpoint of the chiral phase transition in the mu_B-T plane at mu_{iso}=0 moves to the tricritical point of the pion-superfluidity phase transition in the mu_{iso}-T plane at mu_B=0 as mu_{iso} increases. The thermodynamics at small T is controlled by sqrt{sigma^2+pi^2} defined by the chiral and pion condensates, sigma and pi.
We introduce a random matrix model with the symmetries of QCD at finite temperature and chemical potentials for baryon number and isospin. We analyze the phase diagram of this model in the chemical potential plane for different temperatures and quark masses. We find a rich phase structure with five different phases separated by both first and second order lines. The phases are characterized by the pion condensate and the chiral condensate for each of the flavors. In agreement with lattice simulations, we find that in the phase with zero pion condensate the critical temperature depends in the same way on the baryon number chemical potential and on the isospin chemical potential. At nonzero quark mass, we remarkably find that the critical end point at nonzero temperature and baryon chemical potential is split in two by an arbitrarily small isospin chemical potential. As a consequence, there are two crossovers that separate the hadronic phase from the quark-gluon plasma phase at high temperature. Detailed analytical results are obtained at zero temperature and in the chiral limit.
We investigate the phase structure of strongly interacting matter and baryon number fluctuations in the Polyakov loop improved Nambu--Jona-Lasinio (PNJL) model. The calculation shows that both the chiral and deconfinement transitions, as well as their coincidence and separation determine the basic QCD phase structure. The contour maps and the three-dimensional diagrams of the net-baryon kurtosis and skewness present well the trace of QCD phase structure. Comparing with the experimental data, we find that the existence of a critical end point (CEP) of chiral transition is crucial to explain the non-monotonic energy dependence and the large deviation from Poisson baseline of net-proton kurtosis. In particular, the relation between the chiral and deconfinement transitions in the crossover region is also reflected by the baryon number fluctuations. This study shows that the measurements of higher moments of multiplicity distributions of conserved charges are powerful to investigate the criticality and even the chiral and deconfinement transitions in the crossover region.
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