First-order Quark-hadron Phase Transition Research Articles

Merger and Postmerger of Binary Neutron Stars with a Quark-Hadron Crossover Equation of State.

Fully general-relativistic binary-neutron-star (BNS) merger simulations with quark-hadron crossover (QHC) equations of state (EOS) are studied for the first time. In contrast to EOS with purely hadronic matter or with a first-order quark-hadron phase transition (1PT), in the transition region QHC EOS show a peak in sound speed and thus a stiffening. We study the effects of such stiffening in the merger and postmerger gravitational (GW) signals. Through simulations in the binary-mass range 2.5<M/M_{⊙}<2.75, characteristic differences due to different EOS appear in the frequency of the main peak of the postmerger GW spectrum (f_{2}), extracted through Bayesian inference. In particular, we found that (i)for lower-mass binaries, since the maximum baryon number density (n_{max}) after the merger stays below 3-4 times the nuclear-matter density (n_{0}), the characteristic stiffening of the QHC models in that density range results in a lower f_{2} than that computed for the underlying hadronic EOS and thus also than that for EOS with a 1PT; (ii)for higher-mass binaries, where n_{max} may exceed 4-5n_{0} depending on the EOS model, whether f_{2} in QHC models is higher or lower than that in the underlying hadronic model depends on the height of the sound-speed peak. Comparing the values of f_{2} for different EOS and BNS masses gives important clues on how to discriminate different types of quark dynamics in the high-density end of EOS and is relevant to future kilohertz GW observations with third-generation GW detectors.

Dual QCD thermodynamics at finite temperature and chemical potential

A Dual QCD formulation for [Formula: see text] color gauge has been developed in terms of dual gauge potentials, building on our previously published study for the [Formula: see text] case with zero bario-chemical potential [H. C. Chandola, G. Punetha and H. Dehnen, Nucl. Phys. A 945, 226 (2016).] and taking into account the local as well as topological structure of the color gauge group into its dynamics. For the purpose of examining the nonperturbative characteristics of QCD, the dynamical configuration of the resulting dual QCD vacuum and its flux tube configuration have been examined. The thermal behavior of the nonperturbative QCD vacuum has been investigated for exploring the dynamics of quark-hadron phase transition at finite chemical potential. Related thermodynamic quantities and equation of state (EoS) to characterize quark matter have also been discussed within the framework of dual QCD-based hadronic bag which guarantees the critical parameters and the associated critical points for quark-hadron phase transition. These thermodynamic quantities are expected to play important roles in understanding the order of quark-hadron phase transition and are likely to predict the features of a first-order quark-hadron phase transition for finite chemical potential. Moreover, we have investigated the bulk properties of quark matter by constructing the free energy change and the associated surface tension for quark-hadron phase transition. For consistency and compatibility check, we have also compared our results with state-of-the-art three-loop Hard Thermal Loop perturbative results and available lattice QCD results and in the process found reasonable agreements.

Bubble dynamics in a strong first-order quark-hadron transition * *Supported in part by National Natural Science Foundation of China (NSFC) (11675048)

We investigate the dynamics of a strong first-order quark-hadron transition driven by cubic interactions via homogeneous bubble nucleation in the Friedberg-Lee model. The one-loop effective thermodynamic potential of the model and the critical bubble profiles have been calculated at different temperatures and chemical potentials. By taking the temperature and the chemical potential as variables, the evolutions of the surface tension, the typical radius of the critical bubble, and the shift in the coarse-grained free energy in the presence of a nucleation bubble are obtained, and the limit on the reliability of the thin-wall approximation is also addressed accordingly. Our results are compared to those obtained for a weak first-order quark-hadron phase transition; in particular, the spinodal decomposition is relevant.

Perspectives of anisotropic flow measurements at NICA

High-accuracy and high-luminosity measurements of anisotropic flow for various hadron types over full NICA energy range will provide important constraints on the early dynamics of heavy-ion reactions under the conditions where a first-order quark-hadron phase transition may occur. The statistical reach for elliptic flow measurements at NICA is estimated with HYDJET++ heavy-ion event generator.

On the nucleation of hadronic domains in the quark-hadron transition

We present numerical results on bubble profiles, nucleation rates and time evolution for a weakly first-order quark-hadron phase transition in different expansion scenarios. We confirm the standard picture of a cosmological first-order phase transition, in which the phase transition is entirely dominated by nucleation. We also show that, even for expansion rates much lower than those expected in heavy-ion collisions nucleation is very unlikely, indicating that the main phase conversion mechanism is spinodal decomposition.

Quantum chromodynamics phase transition in the early Universe and quark nuggets

A first-order quark hadron phase transition in the early Universe may lead to the formation of quark nuggets. The baryon number distribution of these quark nuggets have been calculated and it has been found that there are sizeable number of quark nuggets in the stable sector. The nuggets can clump and form bigger objects in the mass range of 0.0003M⊙ to 0.12M⊙. It has been discussed that these bigger objects can be possible candidates for cold dark matter.

Observing B-violation in relativistic heavy-ion collisions

Under certain situations, partons formed in heavy-ion collision experiments may expand out forming a shell-like structure. The partons in the outer shell subsequently hadronize, leaving a bubble of pure deconfined vacuum for a first-order quark-hadron phase transition. The bubble collapses and may eventually decay into particles which may thermalize to temperatures exceeding the electroweak transition temperature (100 GeV) at LHC. This will lead to the possibility of unsuppressed electroweak baryon number violating processes.

Spinodal decomposition: An alternate mechanism of phase conversion

The scenario of homogeneous nucleation is investigated for a first-order quark-hadron phase transition in a rapidly expanding background of quark gluon plasma. It is found that significant supercooling is possible before hadronization begins. This study also suggests that spinodal decomposition competes with nucleation and may provide an alternative mechanism for phase conversion.

Inhomogeneous nucleation in a quark-hadron phase transition

The effect of subcritical hadron bubbles on a first-order quark-hadron phase transition is studied. These subcritical hadron bubbles are created due to thermal fluctuations, and can introduce a finite amount of phase mixing (quark phase mixed with hadron phase) even at and above the critical temperature. For reasonable choices of surface tension and correlation length, as obtained from the lattice QCD calculations, we show that the amount of phase mixing at the critical temperature remains below the percolation threshold. Thus, as the system cools below the critical temperature, the transition proceeds through the nucleation of critical-size hadron bubbles from a metastable quark-gluon phase (QGP), within an inhomogeneous background populated by an equilibrium distribution of subcritical hadron bubbles. The inhomogeneity of the medium results in a substantial reduction of the nucleation barrier for critical bubbles. Using the corrected nucleation barrier, we estimate the amount of supercooling for different parameters controlling the phase transition, and briefly discuss its implications to cosmology and heavy-ion collisions.

Scaling behaviour of the multiplicity distribution under first-order quark-hadron phase transition

The multiplicity distribution in small bins is studied within the Ginzburg-Landau description for first-order quark-hadron phase transition. Direct comparison of the distribution with a Poisson one (with the same average) is made. Dynamical factor for the distribution and ratio are studied, and novel scaling behaviours between are found which can be used to detect the formation of quark-gluon plasma.

Multiplicity difference correlators under first-order QGP phase transition

The multiplicity difference correlators between two well-separated bins in high-energy heavy-ion collisions are studied as a means to detect evidence of a first-order quark-hadron phase transition. Analytical expressions for the scaled factorial moments of multiplicity difference distribution are obtained for small bin size with mean multiplicity in the bin within the Ginzburg-Landau description. The scaling behaviours between the moments are still valid, although they behave completely different from the so-called intermittency patterns. A universal exponent is given to describe the dynamical fluctuations in the phase transition in the small limit.

Primordial nucleosynthesis.

With the advent of the new extragalactic deuterium observations, Big Bang nucleosynthesis (BBN) is on the verge of undergoing a transformation. In the past, the emphasis has been on demonstrating the concordance of the BBN model with the abundances of the light isotopes extrapolated back to their primordial values by using stellar and galactic evolution theories. As a direct measure of primordial deuterium is converged upon, the nature of the field will shift to using the much more precise primordial D/H to constrain the more flexible stellar and galactic evolution models (although the question of potential systematic error in 4He abundance determinations remains open). The remarkable success of the theory to date in establishing the concordance has led to the very robust conclusion of BBN regarding the baryon density. This robustness remains even through major model variations such as an assumed first-order quark-hadron phase transition. The BBN constraints on the cosmological baryon density are reviewed and demonstrate that the bulk of the baryons are dark and also that the bulk of the matter in the universe is nonbaryonic. Comparison of baryonic density arguments from Lyman-alpha clouds, x-ray gas in clusters, and the microwave anisotropy are made.

Baryon-number density in hadronic gas models and baryon asymmetry in the early Universe.

We have recently shown that the inclusion of finite-size volume corrections for the hadrons in the hadronic gas phase drastically alters the conclusions regarding isothermal baryon-number fluctuations arising from a first-order quark-hadron phase transition in the early Universe. In this paper we compare in detail the predictions of various existing thermodynamically consistent hadron gas (HG) models for the baryon density in the HG phase and its dependence on the temperature in order to draw a firm conclusion regarding the results obtained in the earlier paper. \textcopyright{} 1996 The American Physical Society.

Cluster growth in two-dimensional quark-hadron phase transition.

The problem of hadronic cluster production in heavy-ion collisions is studied in search for an observable signature of first-order quark-hadron phase transition. The study is carried out by cellular automata in a two-dimensional model of the mixed phase at midrapidity. The clusters are allowed to grow as well as to coalesce upon collision. The distribution of cluster sizes is found to exhibit scaling behavior that is independent of the size of the mixed region, nucleation radius and nucleation probability. The universal scaling index $\gamma=1.86\pm 0.18$ may be used to characterize and identify the phase transition process. Possible connection with self-organized criticality is pointed out.

Scaling behavior in first-order quark-hadron phase transition.

It is shown that in the Ginzburg-Landau description of first-order quark-hadron phase transition the normalized factorial moments exhibit scaling behavior. The scaling exponent \ensuremath{\nu} depends on only one effective parameter g, which characterizes the strength of the transition. For a strong first-order transition, we find \ensuremath{\nu}=1.45. For weak transition it is 1.30 in agreement with the earlier result on second-order transition.

Baryon-number fluctuations in a quark-hadron phase transition.

Isothermal baryon-number fluctuations arising from a first-order quark-hadron phase transition in the early Universe are obtained by including the quark-gluon interactions up to the order [ital g][sub [ital s]][sup 3] in the perturbative QCD coupling constant in the quark-gluon plasma (QGP) phase and the finite-size volume corrections for the hadrons in the hadron-resonance gas (HRG) and their effects on the primordial nucleosynthesis (PNS) are analyzed. The ratio of the baryon-number densities in the QGP and HRG phases at the critical temperature [ital T][sub [ital c]] is larger than one in the range 150 MeV[lt][ital T][sub [ital c]][lt]260 MeV. However, it is far larger than one even when [ital T][sub [ital c]] is outside this range, thus affecting primordial nucleosynthesis significantly.

Cluster production in quark-hadron phase transition in heavy-ion collisions.

The problem of cluster formation and growth in the first-order quark-hadron phase transition in heavy-ion collisions is considered. Behaving as Brownian particles, the clusters carry out random walks and can encounter one another, leading to coalescence and breakup. A simulation of the process in a cellular automaton suggests the possibility of a scaling distribution in the cluster sizes. The experimental determination of the cluster-size distribution is urged as a means to find a clear signature of the phase transition.

Importance of interactions in quark-gluon plasma: Baryon-number density contrast and primordial nucleosynthesis.

We analyze the baryon-number density contrast $R$ between the quark-gluon-plasma (QGP) phase and the hadronic phase during a first-order quark-hadron phase transition in the early Universe. Without the inclusion of baryonic resonances in the hadronic phase, we can reduce $R$ by including interactions between quarks and gluons in the QGP phase. We also show that there is no need to use a large value of the bag constant to lower the value of $R$. Our calculations may be useful in non-standard big-bang nucleosynthesis.

Hadron bubble evolution into the quark sea.

A solution is presented for the evolution of hadron bubbles which nucleate in the quark sea if there is a first-order quark-hadron phase transition at a temperature ${T}_{c}$ on the order of 100 MeV. We make three assumptions: (1) the dominant mechanism for transport of latent heat is radiative, e.g., neutrinos; (2) the distance between nucleation sites is greater than the neutrino mean free path; and (3) the effects of hydrodynamic flow can be neglected. Bubbles nucleate with a characteristic radius $\frac{1 \mathrm{fm}}{\ensuremath{\Delta}}$, where $\ensuremath{\Delta}$ is a dimensionless parameter for the undercooling (we take $\ensuremath{\Delta}\ensuremath{\ge}{10}^{\ensuremath{-}4}$, so that the expansion of the Universe can be neglected). We argue that bubbles grow stably and remain spherical until the radius becomes as large as the neutrino mean free path, $l\ensuremath{\simeq}10$ cm. The growth then becomes diffusion limited and the bubbles become unstable to formation of dendrites, or finger-like structures, because latent heat can diffuse away more easily from long fingers than from spheres. We study the nonlinear evolution of structure with a geometrical model and argue that the hadron bubbles ultimately look like stringy seaweed. The percolation of seaweed-shaped bubbles can leave behind regions of quark phase that are quite small. In fact, one might expect the typical scale to be ${L}_{Q}=l\ensuremath{\simeq}10$ cm. Protons can easily diffuse out of such small regions (and neutrons back in). Thus, these instabilities can lead to important modifications of inhomogeneous nucleosynthesis, which requires ${L}_{Q}\ensuremath{\gtrsim}1$ m.

Cosmology and the neutron lifetime

The standard Big Bang nucleosynthesis arguments are reviewed. The primordial He abundance is inferred from HeC and HeN and HeO correlations. The strengthened Li constraint as well as 2D plus 3He are used to limit the baryon density. The allowed number of neutrino families, N ν is delineated using the new value of τ n = 890 ± 4 s (τ 1 2 = 10.3 min) reported at this meeting. The formal statistical result is N ν = 2.6 ± 0.3 (1 σ), providing a reasonable fit (1.3σ) to three families but making a fourth light ( m ν ⪅ 10 MeV) neutrino family exceedingly unlikely (≳ 4.7 σ) (barring significant systematic errors either in D + 3He, and Li and/or 4He and/or τ n). It is also shown that uncertainties induced by postulating a first-order quark-hadron phase transition do not seriously affect the conclusions.