First-order Deconfinement Phase Transition Research Articles

Thermodynamics of PNJL model at zero temperature in a strong magnetic field

In this paper, the deconfinement and chiral restoration transitions in a strong magnetic field are realized at zero temperature in the Polyakov Nambu-Jona-Lasinio model. We provide the thermodynamic treatment to mimic the deconfinement phase transition at zero temperature together with the entangled scalar and vector interactions coupled with the Polyakov loop. The magnetic catalysis is found by a rising behavior of the critical chemical potential for the first-order deconfinement phase transition. While the magnetic catalysis on the chiral restoration could convert to inverse magnetic catalysis under the running coupling interaction ansatz. Furthermore, the stronger magnetic field makes the possible quarkyonic phase window to be enlarged under the running coupling interaction.

Analytical solution of surface tension of quark-hadron phase transition

By using the finite temperature field theory, the one-loop effective potential and the dynamics of the quantum chromodynamics deconfinement phase transition in the framework of Friedberg-Lee model are studied at finite temperature and density. Our results show that there is a first-order deconfinement phase transition for the full phase diagram, and the critical temperature is about 119.8 MeV for a zero chemical potential whereas the critical chemical is around 256.4 MeV when the temperature is fixed at <i>T</i> = 50 MeV. Moreover, in the thin-wall approximation, we investigate the dynamics of a strong first-order quark-hadron transition via homogeneous bubble nucleation in the Friedberg-Lee model. Under an appropriate boundary condition, the equation of motion for the <inline-formula><tex-math id="M3">\begin{document}$ \sigma $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20220659_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20220659_M3.png"/></alternatives></inline-formula> field is solved, then the evolutions of the bubble critical configuration with radius <inline-formula><tex-math id="M4">\begin{document}$ r $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20220659_M4.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="21-20220659_M4.png"/></alternatives></inline-formula> at different temperatures and densities are calculated. The surface tension, the typical radius of the critical bubble and the shift in the coarse-grained free energy each as a function of temperature and chemical potential are obtained. In order to gain the reliability and advantages of the thin-wall approximation, our analytical results based on the thin-wall approximation are compared with those obtained by the exact numerical method accordingly. Finally, some consequences and possible applications of our results in the quark meson model and Polyakov quark meson model are also presented in the end of this paper.

Deconfinement phase transition in the SU(3) instanton-dyon ensemble

Confinement remains one the most interesting and challenging nonperturbative phenomenon in non-Abelian gauge theories. Recent semiclassical [for $SU(2)$] and lattice (for QCD) studies have suggested that confinement arises from interactions of statistical ensembles of instanton dyons with the Polyakov loop. We extend studies of a semiclassical ensemble of dyons to the $SU(3)$ Yang-Mills theory. We find that such interactions do generate the expected first-order deconfinement phase transition. The properties of the ensemble, including correlations and topological susceptibility, are studied over a range of temperatures above and below ${T}_{c}$. Additionally, the dyon ensemble is studied in the Yang-Mills theory containing an extra trace-deformation term. It is shown that such a term can cause the theory to remain confined and even retain the same topological observables at high temperatures.

Gravitational waves from holographic neutron star mergers

We present simulations of binary neutron star mergers with equations of state (EoSs) that have input from holography, and analyze the spectral properties of the resulting waveforms. These EoSs consist of a standard nuclear matter EoS at low densities, transitioning to a state-of-the-art holographic EoS with first-order deconfinement phase transition in the otherwise intractable high-density regime. Depending on the transition density, the characteristic frequencies in the spectrum produced from the hybrid EoSs are shifted to significantly lower values. Equal-mass binaries with a total mass of $2.8\text{ }\text{ }{M}_{\ensuremath{\bigodot}}$ reach densities in the quark matter phase in the core of the transient hypermassive neutron star, which then induces an immediate gravitational collapse.

End point of the first-order phase transition of QCD in the heavy quark region by reweighting from quenched QCD

We study the end point of the first-order deconfinement phase transition in two and 2+1 flavor QCD in the heavy quark region of the quark mass parameter space. We determine the location of critical point at which the first-order deconfinement phase transition changes to crossover, and calculate the pseudo-scalar meson mass at the critical point. Performing quenched QCD simulations on lattices with the temporal extents Nt=6 and 8, the effects of heavy quarks are determined using the reweighting method. We adopt the hopping parameter expansion to evaluate the quark determinants in the reweighting factor. We estimate the truncation error of the hopping parameter expansion by comparing the results of leading and next-to-leading order calculations, and study the lattice spacing dependence as well as the spatial volume dependence of the result for the critical point. The overlap problem of the reweighting method is also examined. Our results for Nt=4 and 6 suggest that the critical quark mass decreases as the lattice spacing decreases and increases as the spatial volume increases.

Exploring Baryon Rich Matter with Heavy-Ion Collisions

Collisions of heavy nuclei at (ultra-)relativistic energies provide a fascinating opportunity to re-create various forms of matter in the laboratory. For a short extent of time (10-22 s), matter under extreme conditions of temperature and density can exist. In dedicated experiments, one explores the microscopic structure of strongly interacting matter and its phase diagram. In heavy-ion reactions at SIS18 collision energies, matter is substantially compressed (2–3 times ground-state density), while moderate temperatures are reached (T < 70 MeV). The conditions closely resemble those that prevail, e.g., in neutron star mergers. Matter under such conditions is currently being studied at the High Acceptance DiElecton Spectrometer (HADES). Important topics of the research program are the mechanisms of strangeness production, the emissivity of matter, and the role of baryonic resonances herein. In this contribution, we will focus on the important experimental results obtained by HADES in Au+Au collisions at 2.4 GeV center-of-mass energy. We will also present perspectives for future experiments with HADES and CBM at SIS100, where higher beam energies and intensities will allow for the studies of the first-order deconfinement phase transition and its critical endpoint.

Parity Doubling and the Dense-Matter Phase Diagram under Constraints from Multi-Messenger Astronomy

We extend the recently developed hybrid quark–meson–nucleon model by augmenting a six-point scalar interaction and investigate the consequences for neutron-star sequences in the mass–radius diagram. One of the characteristic features of the model is that the chiral symmetry is restored within the hadronic phase by lifting the mass splitting between chiral partner states, before quark deconfinement takes place. At low temperature and finite baryon density, the model predicts a first- or second-order chiral phase transition, or a crossover, depending on the expectation value of a scalar field, and a first-order deconfinement phase transition. We discuss two sets of free parameters, which result in compact-star mass–radius relations that are at tension with the combined constraints for maximum-mass ( 2 M ⊙ ) and the compactness (GW170817). We find that the most preferable mass–radius relations result in isospin-symmetric phase diagram with rather low temperature for the critical point of the chiral phase transition.

Effective Potential Formalism at Finite Temperature in Dual QCD and Deconfilnement Phase Transition

We study the pure-gauge QCD phase transition at filnite temperatures in the dual QCD theory, an effective theory of QCD based on the magnetic symmetry. We formulate the effective thermodynamical potential for filnite temperatures using the path-integral formalism in order to investigate the properties of the pure-gauge QCD vacuum. Thermal effects bring a first-order deconfinement phase transition.

Net-baryon number fluctuations in the hybrid quark-meson-nucleon model at finite density

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.

Deconfinement Phase Transition with External Magnetic Field in the Friedberg—Lee Model**Supported by the National Natural Science Foundation of China under Grant No 11405122, and the China Postdoctoral Science Foundation under Grant No 2014M550483.

The deconfinement phase transition with external magnetic field is investigated in the Friedberg—Lee model. We expand the potential around the two local minima of the first-order deconfinement phase transition and extract the ground state of the system in the frame of functional renormalization group. By solving the flow equations we find that the magnetic field displays a catalysis effect and it becomes more difficult to break through the confinement.

Critical point in the QCD phase diagram for extremely strong background magnetic fields

Lattice simulations have demonstrated that a background (electro)magnetic field reduces the chiral/deconfinement transition temperature of quantum chromodynamics for eB < 1 GeV2. On the level of observables, this reduction manifests itself in an enhancement of the Polyakov loop and in a suppression of the light quark condensates (inverse magnetic catalysis) in the transition region. In this paper, we report on lattice simulations of 1 + 1 + 1-flavor QCD at an unprecedentedly high value of the magnetic field eB = 3.25 GeV2. Based on the behavior of various observables, it is shown that even at this extremely strong field, inverse magnetic catalysis prevails and the transition, albeit becoming sharper, remains an analytic crossover. In addition, we develop an algorithm to directly simulate the asymptotically strong magnetic field limit of QCD. We find strong evidence for a first-order deconfinement phase transition in this limiting theory, implying the presence of a critical point in the QCD phase diagram. Based on the available lattice data, we estimate the location of the critical point.

Spinodal density enhancements in nuclear collisions at the CBM experiment

We discuss a novel approach to describe the evolution of a fireball, created in a high-energy nuclear collision, experiencing spinodal instabilities due to the first-order deconfinement phase transition of quantum chromo dynamics (QCD). We show that initial density fluctuations in these collisions are enhanced in the mechanically unstable region of the QCD phase diagram. In our study we find that the most favorable energy range for observing these density enhancements is at the lower end of the SIS100 accelerator at FAIR, currently under construction. Furthermore we discuss how one can distinguish and constrain different types of QCD phase transitions, one of hadron-quark type and one of liquid-gas type, leading to strong differences in the dynamical evolution of the QCD medium.

An effective chiral hadron–quark equation of state

We construct an effective model for the QCD equation of state, taking into account chiral symmetry restoration as well as the deconfinement phase transition. The correct asymptotic degrees of freedom at the high and low temperature limits are included (quarks ↔ hadrons). The model shows a rapid crossover for both order parameters, as expected from lattice calculations. We then compare the thermodynamic properties of the model at μB = 0 which turn out to be in qualitative agreement with lattice data, while apparent quantitative differences can be attributed to hadronic contributions and excluded-volume corrections. Furthermore we discuss the effects of a repulsive vector-type quark interaction at finite baryon number densities on the resulting phase diagram of the model. Our current model is able to reproduce a first-order liquid–gas phase transition as expected, but does not show any signs of a first-order deconfinement or chiral phase transition. Both transitions rather appear as a very wide crossover in which heavily medium modified hadron coexists with free quarks.

Quantifying zigzag motion of quarks

The quark condensate is calculated in terms of the effective string tension and the constituent quark mass. For 3 colors and 2 light flavors, the constituent mass is bounded from below by the value of 460 MeV. This value is only accessible when the string tension decreases linearly with the Schwinger proper time. For this reason, the Hausdorff dimension of a light-quark trajectory is equal to 4, indicating that these trajectories are similar to branched polymers, which can describe a weak first-order deconfinement phase transition in SU(3) Yang-Mills theory. Using this indication, we develop a gluon-chain model based on such trajectories.

Deconfinement phase transition in compact stars: Maxwell versus Gibbs construction of the mixed phase

We study different realizations of the first-order deconfinement phase transition inside a compact star by comparing the Gibbs and Maxwell construction for the mixed phase. The hadronic sector is described within the relativistic mean field model including hyperons. The quark sector is described by the MIT bag model. We find that these two realizations lead to very different star properties, in particular, the composition of the stellar matter. We also find that for the Maxwell construction there is a sharp discontinuity in the baryon density and the electron chemical potential. We argue that a sharp jump in the electron chemical potential should lead to the redistribution of electrons and formation of strong electric fields around the discontinuity surface.

Thermodynamics for a hadronic gas of fireballs with internal color structures and chiral fields

The thermodynamic partition function for a gas of color-singlet bags consisting of fundamental and adjoint particles in both $\mathrm{U}({N}_{c})$ and $\mathrm{SU}({N}_{c})$ group representations is reviewed in detail. The constituent particle species are assumed to satisfy various thermodynamic statistics. The gas of bags is probed to study the phase transition for nuclear matter in extreme conditions. These bags are interpreted as the Hagedorn states, and they are the highly excited hadronic states produced below the phase transition point to the quark-gluon plasma (QGP). The hadronic density of states has the Gross-Witten critical point and exhibits a third-order phase transition from a hadronic phase dominated by the discrete low-lying hadronic mass spectrum particles to another hadronic phase dominated by the continuous Hagedorn states. The Hagedorn threshold production is found just above the highest known experimental discrete low-lying hadronic mass spectrum. The subsequent Hagedorn phase undergoes a first-order deconfinement phase transition to an explosive QGP. The role of the chiral phase transition in the phases of the discrete low-lying mass spectrum and the continuous Hagedorn mass spectrum is also considered. It is found to be crucial in the phase transition diagram. Alternative scenarios are briefly discussed for the Hagedorn gas undergoing a higher order phase transition through multiple processes of internal color-flavor structure modification.

Dissolved deconfinement: Phase structure of largeNgauge theories with fundamental matter

A class of large $N$ $U(N)$ gauge theories on a compact manifold ${S}^{3}\ifmmode\times\else\texttimes\fi{}\mathbb{R}$ (with possible inclusion of adjoint matter) is known to show first-order deconfinement transition at the deconfinement temperature. This includes the familiar example of pure $YM$ theory and $\mathcal{N}=4$ Supersymmetric Yang-Mills theory. Here we study the effect of introduction of ${N}_{f}$ fundamental matter fields in the phase diagram of the above mentioned gauge theories at small coupling and in the limit of large $N$ and finite ${N}_{f}/N$. We find some interesting features like the termination of the line of first-order deconfinement phase transition at a critical point as the ratio ${N}_{f}/N$ is increased and absence of deconfinement transition thereafter (there is only a smooth crossover). This result may have some implication for QCD, which unlike a pure gauge theory does not show a first-order deconfinement transition and only displays a smooth crossover at the transition temperature.

Center vortex model forSp(2)Yang-Mills theory

The question whether the center vortex picture of the strongly interacting vacuum can encompass the infrared dynamics of both SU(2) as well as Sp(2) Yang-Mills theory is addressed. These two theories contain the same center vortex degrees of freedom, and yet exhibit deconfinement phase transitions of different order. This is argued to be caused by the effective action governing the vortices being different in the two cases. To buttress this argument, a random vortex world-surface model is constructed which reproduces available lattice data characterizing Sp(2) Yang-Mills confinement properties. A new effective action term which can be interpreted in terms of a vortex stickiness serves to realize a first-order deconfinement phase transition, as found in Sp(2) Yang-Mills theory. Predictions are given for the behavior of the spatial string tension at finite temperatures.

Canonical strangeness and distillation effects in hadron production

The strangeness canonical ensemble for Maxwell–Boltzmann statistics is reconsidered for excited nuclear systems with non-vanishing net strangeness. A new recurrence relation method is applied to find the partition function. The method is first generalized to the case of quantum strangeness canonical ensemble. Uncertainties in the calculation of the K+/π+ excitation function are discussed. A new scenario based on the strangeness distillation effect is put forward for a possible explanation of anomalous strangeness production observed at the bombarding energy ∼30 GeV. The peaked maximum in the K+/π+ ratio is considered as a sign of the critical endpoint reached in evolution of the system rather than a latent heat jump emerging from the onset of the first-order deconfinement phase transition.

αsdependence in the equilibration in relativistic heavy-ion collisions

The dependence of the equilibration of the parton plasma on the value of the strong coupling is studied in Au+Au collisions at LHC and at RHIC energies. With increasing coupling, the following are found to happen: (1) both thermal and chemical equilibration speed up, (2) in the final degree of equilibration, only quarks and antiquarks show obvious improvements but not gluons, and (3) the plasma cools much more rapidly. The deconfinement phase transition will therefore take place sooner and it naturally results in the shortening of the parton phase of the plasma. The exact duration of this phase is, however, sensitive to the value of the coupling. A change from ${\ensuremath{\alpha}}_{s}=0.3$ to ${\ensuremath{\alpha}}_{s}=0.5$, for example, reduces the lifetime of the parton phase at LHC by as much as 4.0 fm/$c$. The total generated entropy is another sensitive quantity to the coupling. Larger values of ${\ensuremath{\alpha}}_{s}$ will lead to entropy reduction and therefore reduction both in the duration of the mixed phase, assuming there is a first-order deconfinement phase transition, as well as in the final pion multiplicity. It is shown that the common choice of ${\ensuremath{\alpha}}_{s}=0.3$ is not a good value for the entire duration of the evolution given that the system undergoes substantial changes from the beginning to the time that the deconfinement phase transition is about to take place assumed to be at ${T}_{c}\ensuremath{\sim}200$ MeV. Instead, by using a more consistent simple recipe, the system is allowed to decide its own strength of the interactions which evolves with the system as it should. With this approach, ${\ensuremath{\alpha}}_{s}$ increases with time and this leads to acceleration in the equilibration even as equilibrium is near. This is opposite to the behavior of the equilibration of a molecular gas or ordinary many-body system where the interaction strength is fixed. In such a system, the net interactions will slow down as the system is near equilibrium.