Location Of Critical End Point Research Articles

Locating the critical endpoint of QCD: Mesonic backcoupling effects

We study the effects of pion and sigma meson backcoupling on the chiral order parameters and the QCD phase diagram and determine their effect on the location of the chiral critical endpoint. To this end, we solve a coupled set of truncated Dyson-Schwinger equations for Landau gauge quark and gluon propagators with ${N}_{\mathrm{f}}=2+1$ dynamical quark flavors and explicitly backcoupled mesons. The corresponding meson bound-state properties and the quark-meson Bethe-Salpeter vertices are obtained from their homogeneous Bethe-Salpeter equation. We find chiral-restoration effects of the pion and/or sigma meson backcoupling and observe a (small) shift of the critical endpoint towards smaller chemical potentials. The curvature of the chiral crossover line decreases. Our results indicate that the location of the critical endpoint in the phase diagram is mainly determined by the microscopic degrees of freedom of QCD (in contrast to its critical properties).

Influence of magnetic fields on the stability and the phase transition of quark matter in the Nambu–Jona–Lasinio model

In the presence of the external magnetic fields, we investigate the stability of quark matter as well as the phase transition in the framework of two flavor Nambu–Jona–Lasinio model. The investigation focuses on the magnetic effects with the fixed coupling constant and the running coupling constant G(B, T) depending on both magnetic field and temperature. The dynamical quark mass can be increased by strong magnetic fields and be reduced by the running coupling constant G(B, T). The baryon number density is also increased by strong magnetic fields but is weakly influenced by the running coupling constant G(B, T). Importantly, the stability can be enhanced by the magnetic fields of a proper strength. While it will be reduced by the much weaker or much stronger magnetic fields. The magnetic-field-dependence in the running coupling constant has slight effect on the stability. Finally, the phase transition and the location of critical end point for both coupling cases are numerically shown.

QCD phase diagram in chiral imbalance with self-consistent mean field approximation

We employ a new self-consistent mean field approximation of NJL model, which introduces a free parameter $\alpha$ ($\alpha$ reflects the weight of different interaction channels), to study the effects of the chiral chemical potential $\mu_5$ on QCD phase structure, especially the location of the QCD critical end point (CEP). We find that, at a high temperature, the critical temperature of QCD phase transition smoothly increases with $\mu_5$ at the beginning, and then decreases rapidly. At low temperature and high baryon density region, the increase of the chiral chemical potential will reduce the critical chemical potential of phase transition. The temperature of the CEP shows a non-monotonic dependence on the chiral chemical potential with a long plateau around the maximum. At $\mu_5=0$, we found that the CEP will disappear when the $\alpha$ value is larger than 0.71 and will reappear when the $\mu_5$ increases. This study is important for exploring the QCD phase structure and the location of CEP in chiral imbalanced systems.

Prospects for the study of event-by-event fluctuations at MPD/NICA project

One of the main physics goals of the Multi Purpose Detector (MPD) is to investigate hot and dense baryonic matter in heavy ion collisions at NICA energies to search for the possible critical end point (CEP). Since the location of CEP is not clear the entire accessible region of the QCD phase diagram needs to be explored by scanning the full range of available beam energies. In case of CEP existence it can be observed by abnormal fluctuations of various quantities such as net-proton multiplicity. This task requires excellent particle identification (PID) capability over as large as possible phase space volume. The identification of charged hadrons is achieved at the momenta of 0:1 – 3 GeV/c. The results of hadron identification and preliminary possibility estimation of the study of event-by-event fluctuations at MPD will be presented.

Finite-volume effects on phase transition in the Polyakov-loop extended Nambu–Jona-Lasinio model with a chiral chemical potential

To investigate the finite-volume effects on the chiral symmetry restoration and the deconfinement transition for a quantum chromodynamics (QCD) system with [Formula: see text] (two quark flavors), we apply the Polyakov-loop extended Nambu–Jona-Lasinio model by introducing a chiral chemical potential [Formula: see text] artificially. The final numerical results indicate that the introduced chiral chemical potential does not change the critical exponents, but shifts the location of critical end point (CEP) significantly; the ratios for the chiral chemical potentials and temperatures at CEP, [Formula: see text] and [Formula: see text], are significantly affected by the system size [Formula: see text]. The behavior is that [Formula: see text] increases slowly with [Formula: see text] when [Formula: see text] is “large” and [Formula: see text] decreases first and then increases with [Formula: see text] when [Formula: see text] is “small.” It is also found that for a fixed [Formula: see text], there is a [Formula: see text], where the critical end point vanishes and the whole phase diagram becomes a crossover when [Formula: see text]. Therefore, we suggest that for the heavy-ion collision experiments, which is to study the possible location of CEP, the finite-volume behavior should be taken into account.

Revisiting the phase structure of the Polyakov-quark-meson model in the presence of vacuum fermion fluctuation

We have considered the contribution of fermionic vacuum loop in the effective potential of Polyakov loop extended Quark Meson Model (PQM) for the two quark flavour case and explored the phase structure and thermodynamics of the resulting PQMVT model (Polyakov Quark Meson Model with Vacuum Term) in detail at non zero as well as zero chemical potential. The temperature variations of order parameters and their derivatives have been calculated and the phase diagram together with the location of critical end point (CEP) has been obtained in $\mu$, and $T$ plane in both the models PQMVT and PQM. The PQMVT model analysis has been compared with the calculations in PQM model in order to bring out the effect of fermionic vacuum term on the physical observables. We notice that the critical end point (CEP) which is located near the temperature axis at ($\mu=81.0$, $T = 167$ MeV) in the PQM model gets shifted close to the chemical potential axis at ($\mu_{CEP}=294.7$, $T_{CEP}=84.0$ MeV) in the PQMVT model calculations of the phase diagram. Since it emerges from a background of second order transition in the chiral limit of massless quarks, the crossover occurring at $\mu$ = 0 in PQMVT model for the realistic case of explicitly broken chiral symmetry, has been identified as quite a soft and smooth transition. We have presented and compared the results for temperature variations of thermodynamic observables at zero and different non-zero quark chemical potentials. It is noticed that the presence of fermionic vacuum term in the effective potential leads to a smoother and slower temperature variation of thermodynamic quantities.