Special Issue "Quark-Gluon Plasma in the Early Universe and in Ultra-Relativistic Heavy-Ion Collisions"

A special issue of Universe (ISSN 2218-1997).

Deadline for manuscript submissions: closed (30 June 2017).

Special Issue Editors

Dr. Roman Pasechnik
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Guest Editor
Department of Astronomy and Theoretical Physics, Lund University, 221 00 Lund, Sweden
Interests: subatomic physics; astronomy; astrophysics and cosmology; grand unification; Higgs physics; supersymmetry; electroweak physics; beyond the standard model; composite models; physical vacuum; quasiclassical gravity; cosmic inflation models; heavy ion collisions; hard production processes
Special Issues and Collections in MDPI journals
Dr. José Eliel Camargo-Molina
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Guest Editor
Department of Astronomy and Theoretical Physics, Lund University, Sweden
Dr. António Pestana Morais
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Guest Editor

Special Issue Information

Dear Colleagues,

The theory of strong interactions, Quantum Chromo Dynamics (QCD), is an organic part of the Standard Model (SM) of Particle Physics, which is being validated by many theoretical and experimental studies. Powerful experimental facilities, such as the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC), currently push particle energy, multiplicity, intensity, and precision limits to the furthest ever frontiers. The latter provides the means for progress in a very broad range of topics, performing precision tests of the QCD theory in extreme conditions. While the QCD theory and related phenomenology aspects are being intensively studied in laboratory measurements, possible connections of this important layer of knowledge to Cosmology and processes in the early Universe remain rather vague and largely unexplored. In particular, the emergence of a new state of matter called the quark-gluon plasma (QGP) at RHIC and LHC is often declared to provide an important source of empirical knowledge to what the Universe looked like in the first few moments after the Big Bang, however, the latter still remains a great mystery.

Self-interactions of colour charged particles lead to various collective motion effects and QCD phases. For example, the nuclear matter heated up to about 100 billion degrees turns into vapour, the hadron gas, but it is heated to two trillion degrees, under certain conditions, such a gas turns to a liquid again, the QGP, which is, in fact, the most perfect liquid ever observed. Indeed, this is an experimental observation that the quark-gluon plasma is not a gas, but a liquid with almost zero viscosity when the mean free time of quarks and gluons in the QGP is comparable to the average interparticle spacing. The theoretical and experimental investigation of the QCD phase diagram, in particular, the QGP formation mechanism and dynamical properties, is one of the foremost trends in modern high energy physics and Cosmology. Such important critical phenomena as the initial and final state energy loss, initial state (Color Glass Condensate) formation and saturation effects, nuclear suppression, jet quenching, QCD phase transition and critical temperature, elliptic flow, thermodynamic fluctuations, QCD equation of state at non-zero baryon chemical potential and shear viscosity, hadronisation of QGP, real-time dynamics of the gluon condensate and QGP, etc. are the subject of special interest at an intersection of two big research fields—heavy ion collider physics and physics of early Universe.

Dr. Roman Pasechnik
Dr. José Eliel Camargo-Molina
Dr. António Pestana Morais
Guest Editors

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Published Papers (10 papers)

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Research

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Open AccessArticle
The Sounds of the Little and Big Bangs
Universe 2017, 3(4), 75; https://doi.org/10.3390/universe3040075 - 01 Nov 2017
Cited by 3 | Viewed by 1353
Abstract
Studies on heavy ion collisions have discovered that tiny fireballs of a new phase of matter—quark gluon plasma (QGP)—undergo an explosion, called the Little Bang. In spite of its small size, not only is it well described by hydrodynamics, but even small perturbations [...] Read more.
Studies on heavy ion collisions have discovered that tiny fireballs of a new phase of matter—quark gluon plasma (QGP)—undergo an explosion, called the Little Bang. In spite of its small size, not only is it well described by hydrodynamics, but even small perturbations on top of the explosion turned out to be well described by hydrodynamical sound modes. The cosmological Big Bang also went through phase transitions, related with Quantum Chromodynamics (QCD) and electroweak/Higgs symmetry breaking, which are also expected to produce sounds. We discuss their subsequent evolution and hypothetical inverse acoustic cascade, amplifying the amplitude. Ultimately, the collision of two sound waves leads to the formation of one gravity waves. We briefly discuss how these gravity waves can be detected. Full article
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Open AccessArticle
Fractal Structure of Hadrons: Experimental and Theoretical Signatures
Universe 2017, 3(3), 62; https://doi.org/10.3390/universe3030062 - 26 Aug 2017
Cited by 8 | Viewed by 1391
Abstract
One important ingredient in the study of cosmological evolution is the equation of state of the primordial matter formed in the first stages of the Universe. It is believed that the first matter produced was of hadronic nature, probably the quark–gluon plasma which [...] Read more.
One important ingredient in the study of cosmological evolution is the equation of state of the primordial matter formed in the first stages of the Universe. It is believed that the first matter produced was of hadronic nature, probably the quark–gluon plasma which has been studied in high-energy collisions. There are several experimental indications of self-similarity in hadronic systems—in particular in multiparticle production at high energies. Theoretically, this property was associated with the dynamics of particle production, but it is also possible to relate self-similarity to the hadron structure—in particular to a fractal structure of this system. In doing so, it is found that the thermodynamics of hadron systems at equilibrium must present specific properties that are indeed supported by data. In particular, the well-known self-consistence principle proposed by Hagedorn 50 years ago is shown to be valid, and can correctly describe experimental distributions, mass spectrum of observed particles, and other properties of the hadronic matter. In the present work, a review of the theoretical developments related to the thermodynamical properties of hadronic matter and its applications in other fields is presented. Full article
Open AccessArticle
Mirror QCD and Cosmological Constant
Universe 2017, 3(2), 43; https://doi.org/10.3390/universe3020043 - 08 May 2017
Cited by 6 | Viewed by 1742
Abstract
An analog of Quantum Chromo Dynamics (QCD) sector known as mirror QCD (mQCD) can affect the cosmological evolution due to a non-trivial contribution to the Cosmological Constant analogous to that induced by the ground state in non-perturbative QCD. In this work, we explore [...] Read more.
An analog of Quantum Chromo Dynamics (QCD) sector known as mirror QCD (mQCD) can affect the cosmological evolution due to a non-trivial contribution to the Cosmological Constant analogous to that induced by the ground state in non-perturbative QCD. In this work, we explore a plausible hypothesis for trace anomalies cancellation between the usual QCD and mQCD. Such an anomaly cancellation between the two gauge theories, if it exists in Nature, would lead to a suppression or even elimination of their contributions to the Cosmological Constant. The trace anomaly compensation condition and the form of the non-perturbative mQCD coupling constant in the infrared limit have been proposed by analysing a partial non-perturbative solution of the Einstein–Yang-Mills equations of motion. Full article
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Open AccessArticle
Initial Energy Density of √s = 7 and 8 TeV p–p Collisions at the LHC
Universe 2017, 3(1), 9; https://doi.org/10.3390/universe3010009 - 11 Feb 2017
Cited by 10 | Viewed by 2010
Abstract
Results from the Relativistic Heavy Ion Colloder (RHIC) and the Large Hadron Collider (LHC) experiments show that in relativistic heavy ion collisions, a new state of matter, a strongly interacting perfect fluid, is created. Accelerating, exact and explicit solutions of relativistic hydrodynamics allow [...] Read more.
Results from the Relativistic Heavy Ion Colloder (RHIC) and the Large Hadron Collider (LHC) experiments show that in relativistic heavy ion collisions, a new state of matter, a strongly interacting perfect fluid, is created. Accelerating, exact and explicit solutions of relativistic hydrodynamics allow for a simple and natural description of this medium. A finite rapidity distribution arises from these solutions, leading to an advanced estimate of the initial energy density of high energy collisions. These solutions can be utilized to describe various aspects of proton–proton collisions, as originally suggested by Landau. We show that an advanced estimate based on hydrodynamics yields an initial energy density in s = 7 and 8 TeV proton–proton (p–p) collisions at the LHC on the same order as the critical energy density from lattice Quantum Chromodynamics (QCD). The advanced estimate yields a corresponding initial temperature that is around the critical temperature from QCD and the Hagedorn temperature. The multiplicity dependence of the estimated initial energy density suggests that in high multiplicity p–p collisions at the LHC, there is large enough initial energy density to create a non-hadronic perfect fluid. Full article
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Open AccessArticle
Quark Deconfinement in Rotating Neutron Stars
Universe 2017, 3(1), 5; https://doi.org/10.3390/universe3010005 - 24 Jan 2017
Cited by 12 | Viewed by 2108
Abstract
In this paper, we use a three flavor non-local Nambu–Jona-Lasinio (NJL) model, an improved effective model of Quantum Chromodynamics (QCD) at low energies, to investigate the existence of deconfined quarks in the cores of neutron stars. Particular emphasis is put on the possible [...] Read more.
In this paper, we use a three flavor non-local Nambu–Jona-Lasinio (NJL) model, an improved effective model of Quantum Chromodynamics (QCD) at low energies, to investigate the existence of deconfined quarks in the cores of neutron stars. Particular emphasis is put on the possible existence of quark matter in the cores of rotating neutron stars (pulsars). In contrast to non-rotating neutron stars, whose particle compositions do not change with time (are frozen in), the type and structure of the matter in the cores of rotating neutron stars depends on the spin frequencies of these stars, which opens up a possible new window on the nature of matter deep in the cores of neutron stars. Our study shows that, depending on mass and rotational frequency, up to around 8% of the mass of a massive neutron star may be in the mixed quark-hadron phase, if the phase transition is treated as a Gibbs transition. We also find that the gravitational mass at which quark deconfinement occurs in rotating neutron stars varies quadratically with spin frequency, which can be fitted by a simple formula. Full article
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Open AccessArticle
Baryon Number Transfer Could Delay Quark–Hadron Transition in Cosmology
Universe 2016, 2(4), 32; https://doi.org/10.3390/universe2040032 - 13 Dec 2016
Cited by 1 | Viewed by 1780
Abstract
In the early Universe, strongly interacting matter was a quark–gluon plasma. Both lattice computations and heavy ion collision experiments, however, tell us that, in the absence of chemical potentials, no plasma survives at T < 150 MeV. The cosmological Quark–Hadron transition, however, [...] Read more.
In the early Universe, strongly interacting matter was a quark–gluon plasma. Both lattice computations and heavy ion collision experiments, however, tell us that, in the absence of chemical potentials, no plasma survives at T < 150 MeV. The cosmological Quark–Hadron transition, however, seems to have been a crossover; cosmological consequences envisaged when it was believed to be a phase transition no longer hold. In this paper, we discuss whether even a crossover transition can leave an imprint that cosmological observations can seek or, vice versa, if there are questions cosmology should address to QCD specialists. In particular, we argue that it is still unclear how baryons (not hadrons) could form at the cosmological transition. A critical role should be played by diquark states, whose abundance in the early plasma needs to be accurately evaluated. We estimate that, if the number of quarks belonging to a diquark state, at the beginning of the cosmological transition, is < 1 : 10 6 , its dynamics could be modified by the process of B-transfer from plasma to hadrons. In turn, by assuming B-transfer to cause just mild perturbations and, in particular, no entropy input, we study the deviations from the tracking regime, in the frame of SCDEW models. We find that, in some cases, residual deviations could propagate down to primeval nuclesynthesis. Full article
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Open AccessArticle
Predictions for Bottomonia Suppression in 5.023 TeV Pb-Pb Collisions
Universe 2016, 2(3), 16; https://doi.org/10.3390/universe2030016 - 25 Aug 2016
Cited by 50 | Viewed by 2297
Abstract
We compute the suppression of the bottomonia states Υ ( 1 S ) , Υ ( 2 S ) , Υ ( 3 S ) , χ b ( 1 P ) , χ b ( 2 P ) , and χ b [...] Read more.
We compute the suppression of the bottomonia states Υ ( 1 S ) , Υ ( 2 S ) , Υ ( 3 S ) , χ b ( 1 P ) , χ b ( 2 P ) , and χ b ( 3 P ) states in Large Hadron Collider (LHC) s N N = 5.023 TeV Pb-Pb collisions. For the background evolution we use 3+1d anisotropic hydrodynamics with conditions extrapolated from s N N = 2.76 TeV and we self-consistently compute bottomonia decay rates including non-equilibrium corrections to the interaction potential. For our final results, we make predictions for R A A as function of centrality, rapidity, and p T for the Υ ( 1 S ) and Υ ( 2 S ) states, including feed down effects. In order to assess the dependence on some of the model assumptions, we vary the shear viscosity-to-entropy density ratio, 4 π η / s { 1 , 2 , 3 } , and the initial momentum-space anisotropy parameter, ξ 0 { 0 , 10 , 50 } , while holding the total light hadron multiplicity fixed. Full article
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Review

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Open AccessReview
Monopole-Based Scenarios of Confinement and Deconfinement in 3D and 4D
Universe 2017, 3(2), 50; https://doi.org/10.3390/universe3020050 - 19 Jun 2017
Cited by 2 | Viewed by 2025
Abstract
This review discusses confinement, as well as the topological and critical phenomena, in the gauge theories which provide the condensation of magnetic monopoles. These theories include the 3D SU(N) Georgi-Glashow model, the 4D [U(1)] N - 1 -invariant compact QED , [...] Read more.
This review discusses confinement, as well as the topological and critical phenomena, in the gauge theories which provide the condensation of magnetic monopoles. These theories include the 3D SU(N) Georgi-Glashow model, the 4D [U(1)] N - 1 -invariant compact QED , and the [U(1)] N - 1 -invariant dual Abelian Higgs model. After a general introduction to the string models of confinement, an analytic description of this penomenon is provided at the example of the 3D SU(N) Georgi-Glashow model, with a special emphasis placed on the so-called Casimir scaling of k-string tensions in that model. We further discuss the string representation of the 3D [U(1)] N - 1 -invariant compact QED, as well as of its 4D generalization with the inclusion of the Θ -term. We compare topological effects, which appear in the latter case, with those that take place in the 3D QED extended by the Chern-Simons term. We further discuss the string representation of the ’t Hooft-loop average in the [U(1)] N - 1 -invariant dual Abelian Higgs model extended by the Θ -term, along with the topological effects caused by this term. These topological effects are compared with those occurring in the 3D dual Abelian Higgs model (i.e., the dual Landau-Ginzburg theory) extended by the Chern-Simons term. In the second part of the review, we discuss critical properties of the weakly-coupled 3D confining theories. These theories include the 3D compact QED, along with its fermionic extension, and the 3D Georgi-Glashow model. Full article
Open AccessReview
Phenomenological Review on Quark–Gluon Plasma: Concepts vs. Observations
Universe 2017, 3(1), 7; https://doi.org/10.3390/universe3010007 - 27 Jan 2017
Cited by 44 | Viewed by 3723
Abstract
In this review, we present an up-to-date phenomenological summary of research developments in the physics of the Quark–Gluon Plasma (QGP). A short historical perspective and theoretical motivation for this rapidly developing field of contemporary particle physics is provided. In addition, we introduce and [...] Read more.
In this review, we present an up-to-date phenomenological summary of research developments in the physics of the Quark–Gluon Plasma (QGP). A short historical perspective and theoretical motivation for this rapidly developing field of contemporary particle physics is provided. In addition, we introduce and discuss the role of the quantum chromodynamics (QCD) ground state, non-perturbative and lattice QCD results on the QGP properties, as well as the transport models used to make a connection between theory and experiment. The experimental part presents the selected results on bulk observables, hard and penetrating probes obtained in the ultra-relativistic heavy-ion experiments carried out at the Brookhaven National Laboratory Relativistic Heavy Ion Collider (BNL RHIC) and CERN Super Proton Synchrotron (SPS) and Large Hadron Collider (LHC) accelerators. We also give a brief overview of new developments related to the ongoing searches of the QCD critical point and to the collectivity in small (p + p and p + A) systems. Full article
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Open AccessReview
World-Line Formalism: Non-Perturbative Applications
Universe 2016, 2(4), 28; https://doi.org/10.3390/universe2040028 - 28 Nov 2016
Cited by 2 | Viewed by 2585
Abstract
This review addresses the impact on various physical observables which is produced by confinement of virtual quarks and gluons at the level of the one-loop QCD diagrams. These observables include the quark condensate for various heavy flavors, the Yang-Mills running coupling with an [...] Read more.
This review addresses the impact on various physical observables which is produced by confinement of virtual quarks and gluons at the level of the one-loop QCD diagrams. These observables include the quark condensate for various heavy flavors, the Yang-Mills running coupling with an infra-red stable fixed point, and the correlation lengths of the stochastic Yang-Mills fields. Other non-perturbative applications of the world-line formalism presented in the review are devoted to the determination of the electroweak phase-transition critical temperature, to the derivation of a semi-classical analogue of the relation between the chiral and the gluon QCD condensates, and to the calculation of the free energy of the gluon plasma in the high-temperature limit. As a complementary result, we demonstrate Casimir scaling of k-string tensions in the Gaussian ensemble of the stochastic Yang-Mills fields. Full article
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