Free Quarks Research Articles

Quarkyonic equation of state with momentum-dependent interaction and neutron star structure

The structure and basic properties of dense nuclear matter still remain one of the open problems of Physics. In particular, the composition of the matter that composes neutron stars is under theoretical and experimental investigation. Among the theories that have been proposed, apart from the classical one where the composition is dominated by hadrons, the existence or coexistence of free quark matter is a dominant guess. An approach towards this solution is the phenomenological view according to which the existence of quarkyonic matter plays a dominant role in the construction of the equation of state (EOS). According to it the structure of the EOS is based on the existence of the quarkyonic particle which is a hybrid state of a particle that combines properties of hadronic and quark matter with a corresponding representation in momentum space. In this paper we propose a phenomenological model for quarkyonic matter, borrowed from corresponding applications in hadronic models, where the interaction in the quarkyonic matter depends not only on the position but also on the momentum of the quarkyonic particles. This consideration, as we demonstrate, can have a remarkable consequence on the shape of the EOS and thus on the properties of neutron stars, offering a sufficiently flexible model. Comparison with recent observational data can place constraints on the parameterization of the particular model and help improve its reliability.

Approaching the Conformal Limit of Quark Matter with Different Chemical Potentials

We study in detail the influence of different chemical potentials (baryon, electric charge, strange, and neutrino) on how and how fast a free gas of quarks in the zero-temperature limit reaches the conformal limit. We discuss the influence of non-zero masses, the inclusion of leptons, and different constraints, such as charge neutrality, zero-net strangeness, and fixed lepton fraction. We also investigate for the first time how the symmetry energy of the system under some of these conditions approaches the conformal limit. We find that the inclusion of all quark masses (even the light ones) can produce different results depending on the chemical potential values or constraints assumed. A positive or negative deviation of 10% from the pressure of free massless quarks with the same chemical potential was found to take place as low as μB=77 to as high as 48,897 MeV. This illustrates the fact that the “free” or conformal limit is not a unique description. Finally, we briefly discuss what kind of corrections are expected from perturbative QCD as one goes away from the conformal limit.

Proto-strange quark stars from density-dependent quark mass model

In this paper, we investigate the evolution of strange quark stars (SQS) from birth as proto-strange quark stars to maturity as stable SQSs at a zero temperature. We assume that self-bound free quarks form entirely the compact star and study its evolution through a series of snapshots using a density-dependent quark mass model. We consider β\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\beta $$\\end{document}-equilibrated stellar matter at two major stages of the star’s evolution: neutrino trapped regime and neutrino transparent regime during the deleptonization and cooling processes of the star. We fix the entropy density per baryon and the lepton fraction to investigate the nuclear equation of state (EoS), particle distribution, temperature profile inside the star, sound velocity, polytropic index, and the structure of the star. Our results show that stars with higher neutrino concentrations are slightly more massive than the neutrino-poor ones along the evolution lines of the SQS. We obtain EoSs in agreement with the conformal boundary set through sound velocity, and also the 2 M⊙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_\\odot $$\\end{document} mass constraint for NSs was satisfied at all stages of the star’s evolution.

Equation of State of Quark–Gluon Matter in the Clustering-of-Color-Sources Approach

In the first few microseconds after the Big Bang, the hot dense matter was in the form of quark–gluon plasma consisting of free quarks and gluons. By colliding heavy nuclei at RHIC and LHC at a velocity close to the speed of light, we were able to recreate primordial matter and observe that matter after expansion and cooling. In the present work, we have analyzed the transverse-momentum spectra of charged particles in high-multiplicity pp collisions at LHC energies s= 5.02 and 13 TeV, published by the ALICE Collaboration, using the Color-String Percolation Model. For heavy ions, Pb–Pb at sNN= 2.76 and 5.02 TeV along with Xe–Xe at sNN= 5.44 TeV have been analyzed. The initial temperature was extracted both in low- and high-multiplicity events in pp collisions. For A−A collisions, the temperature was obtained as a function of centrality. A universal scaling in the temperature from pp and A−A collisions was obtained when multiplicity was scaled by the transverse interaction area. For the higher-multiplicity events in pp collisions at s= 5.02 and 13 TeV, the initial temperature was above the universal hadronization temperature and was consistent with the creation of deconfined matter. From the measured energy density ε and the temperature, the dimensionless quantity ε/T4 was obtained, to obtain the degree of freedom of the deconfined matter.

Influence of hyperon–hyperon interaction on the properties of neutron stars

The properties of neutron stars are studied in a composite model of the strong interaction. In the regime of low to medium baryonic densities a covariant hadronic model is adopted which includes an exclusive channel for the hyperon–hyperon interaction mediated by hidden strangeness mesons, which in turn couple to other mesons through polynomial vertices. The new coupling constants are subject to phenomenological constraints. The presence of free quarks in the core of the star is considered by using the Nambu–Jona Lasinio model supplemented with a vector interaction. The deconfinement process is described by a continuous coexistence of phases. Several structure parameters of neutron stars, such as mass-radius relation, moment of inertia, tidal deformability, and the propagation of nonradial f and g-modes within the relativistic Cowling approximation are studied. The predictions of the model are in good agreement with recent observational data, in particular the maximum inertial mass is greater than the observational lower limit of two solar masses.

Quarkyonic matter and applications in neutron stars

The structure and basic properties of dense nuclear matter still remain one of the open problems of physics. In particular, the composition of the matter that composes neutron stars is under theoretical and experimental investigation. Among the theories that have been proposed, apart from the classical one where the composition is dominated by hadrons, the existence or coexistence of free quark matter is a dominant guess. An approach towards this solution is the phenomenological view according to which the existence of quarkyonic matter plays a dominant role in the construction of the equation of state (EOS). In this paper we propose a phenomenological model for quarkyonic matter, borrowed from corresponding applications in hadronic models, where the interaction in the quarkyonic matter depends not only on the position but also on the momentum of the quarkynions. This consideration, as we demonstrate, can have a dramatic consequence on the shape of the EOS and thus on the properties of neutron stars.

Kinematic power corrections in TMD factorization theorem

This work is dedicated to the study of power expansion in the transverse momentum dependent (TMD) factorization theorem. Each genuine term in this expansion gives rise to a series of kinematic power corrections (KPCs). All terms of this series exhibit the same properties as the leading term and share the same nonperturbative content. Among various power corrections, KPCs are especially important since they restore charge conservation and frame invariance, which are violated at a fixed power order. I derive and sum a series of KPCs associated with the leading-power term of the TMD factorization theorem. The resulting expression resembles a hadronic tensor computed with free massless quarks while still satisfying a proven factorization statement. Additionally, I provide an explicit check of this novel form of factorization theorem at the next-to-leading order (NLO) and demonstrate the restoration of the frame-invariant argument of the leading-power coefficient function. Numerical estimations show that incorporating the summed KPCs into the cross-section leads to an almost constant shift, which may help to explain the observed challenges in the TMD phenomenology.

New mass limit of a strange star admitting a colour flavor locked equation of state

A class of strange stars is analysed in the present article in hydrostatic equilibrium, whose state is defined by a CFL phase equation of state. We have compared our results with those obtained from the MIT equation of state for strange quark matter, which is regarded as free particles. We have noted that if we consider quarks to form a cooper pair and if their description is made by the CFL equation of state, the maximum mass of strange star reaches a value as high as 3.61 M⊙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$M_{\\odot }$$\\end{document}. This value is well above the value of 2.03 M⊙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$M_{\\odot }$$\\end{document} obtained by using the MIT bag equation of state for massless free quarks. Both the maximum masses are determined by solving the TOV equation for different values of the strange quark mass ms\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$m_s$$\\end{document}. Thus, the inclusion of the possibility of quark pair formation in the theory permits us to accommodate a wider class of compact objects such as PSR J1614-2230, PSR J0740+6620, PSR J0952-0607 etc. and the mass of the companion star in the GW190814 event in our model. The consideration of such a high value of mass is hardly theoretically obtainable from normal strange star models in general relativity even with a fast rotation effect. The object PSR J0952-0607 is found to be the fastest and heaviest pulsar in the disk of Milky Way Galaxy, having a mass of 2.35 M⊙\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$M_{\\odot }$$\\end{document}, which may be predicted in our model, as observational evidence supports the existence of strange quark matter in its composition.

Confinement in QCD and generic Yang-Mills theories with matter representations

We derive the low-energy limit of quantum chromodynamics (QCD) and provide evidence that in the 't Hooft limit, i.e. for a very large number of colors and increasing 't Hooft coupling, quark confinement is recovered. The low energy limit of the theory turns out to be a non-local Nambu–Jona-Lasinio (NJL) model. The effect of non-locality, arising from a gluon propagator that fits quite well to the profile of an instanton liquid, is to produce a phase transition from a chiral condensate to an instanton liquid, as the coupling increases with lower momentum. This phase transition suffices to move the poles of the quark propagator to the complex plane. As a consequence, free quarks are no longer physical states in the spectrum of the theory.

Quarkyonic or baryquark matter? On the dynamical generation of momentum space shell structure

We study the equation of state of a mixture of (quasi-)free constituent quarks and nucleons with hard-core repulsion at zero temperature. Two opposite scenarios for the realization of the Pauli exclusion principle are considered: (i) a Fermi sea of quarks surrounded by a shell of baryons – the quarkyonic matter, and (ii) a Fermi sea of nucleons surrounded by a shell of quarks which we call baryquark matter. In both scenarios, the sizes of the Fermi sea and shell are fixed through energy minimization at fixed baryon number density. While both cases yield a qualitatively similar transition from hadronic to quark matter, we find that baryquark matter is energetically favored in this setup and yields a physically acceptable behavior of the speed of sound without the need to introduce an infrared regulator. In order to retain the theoretically more appealing quarkyonic matter as the preferred form of dense QCD matter will thus require modifications to the existing dynamical generation mechanisms, such as, for example, the introduction of momentum-dependent nuclear interactions.

Quark confinement in QCD in the 't Hooft limit

We treat quantum chromodynamics (QCD) using a set of Dyson-Schwinger equations derived, in differential form, with the Bender-Milton-Savage technique. In this way, we are able to derive the low energy limit that assumes the form of a non-local Nambu-Jona-Lasinio model. The corresponding gap equation is then studied to show that such a model has no free quarks in the low-energy limit.

Analyzing N-Point Energy Correlators inside Jets with CMS Open Data.

Jets of hadrons produced at high-energy colliders provide experimental access to the dynamics of asymptotically free quarks and gluons and their confinement into hadrons. In this Letter, we show that the high energies of the Large Hadron Collider (LHC), together with the exceptional resolution of its detectors, allow multipoint correlation functions of energy flow operators to be directly measured within jets for the first time. Using Open Data from the CMS experiment, we show that reformulating jet substructure in terms of these correlators provides new ways of probing the dynamics of QCD jets, which enables direct imaging of the confining transition to free hadrons as well as precision measurements of the scaling properties and interactions of quarks and gluons. This opens a new era in our understanding of jet substructure and illustrates the immense unexploited potential of high-quality LHC data sets for elucidating the dynamics of QCD.

Revisiting inclusive decay widths of charmed mesons

Determining for the first time the Darwin operator contribution for the non-leptonic charm-quark decays and using new non-perturbative results for the matrix elements of ∆C = 0 four-quark operators, including eye-contractions, we present a comprehensive study of the lifetimes of charmed mesons and inclusive semileptonic decay rates as well as the ratios, within the framework of the Heavy Quark Expansion (HQE). We find good agreement with experiment for the ratio τ(D+)/τ(D0), for the total {D}_s^{+} -meson decay rate, for the semileptonic rates of all three mesons D0, D+ and {D}_s^{+} , and for the semileptonic ratio {Gamma}_{sl}^{D^{+}}/{Gamma}_{sl}^{D^0} . The total decay rates of the D0 and D+ mesons are underestimated in our HQE approach and we suspect that this is due to missing higher-order QCD corrections to the free charm quark decay and the Pauli interference contribution. For the SU(3)F breaking ratios tau left({D}_s^{+}right)/tau left({D}^0right) and {Gamma}_{sl}^{D_s^{+}}/{Gamma}_{sl}^{D^0} our predictions lie closer to one than experiment. This might originate from the poor knowledge of the non-perturbative parameters {mu}_G^2 , {mu}_{uppi}^2 and {rho}_D^3 in the D0 and {D}_s^{+} systems. These parameters could be determined by experimental studies of the moments of inclusive semileptonic D meson decays.

Chiralspin symmetry and confinement

Interesting lattice QCD simulations at high temperature in QCD and particular truncated studies have shown the emergence of an unexpected group symmetry, so called chiralspin. However this is not a symmetry of the QCD action for free quarks, which makes unclear the transition to deconfinement at high temperature in QCD. Therefore we try to redefine this group so that is a symmetry of free quark action and it is consistent with the presence of deconfinement in QCD.

Chiral Symmetry Restoration Using the Running Coupling Constant from the Light-Front Approach to QCD

In this work, the distance between a quark-antiquark pair is analyzed through both the confinement potential and the hadronic total cross- section. Using the Helmholtz free energy, the entropy is calculated near the minimum of the total cross-section through the confinement potential. A fitting procedure for the proton-proton total cross- section is carried out, defining the fit parameters. Therefore, the only remaining free parameter in the model is the mass-scale к used to define the running coupling constant of the light-front the approach to QCD. The mass scale controls the distance r between the quark-antiquark pair and, under some conditions, allows the appearance of free quarks even within the confinement regime of QCD.

Studying the potential of QQq at finite temperature in a holographic model * *Supported by the National Natural Science Foundation of China (12175100, 11975132) and the Research Foundation of Education Bureau of Hunan Province, China (21B0402, 21A0280, 20C1594)

Using gauge/gravity duality, we investigate the string breaking and dissolution of two heavy quarks coupled to a light quark at finite temperature. It is found that three configurations of QQqexist with the increase in separation distance for heavy quarks in the confined phase. Furthermore, string breaking occurs at the distance ( ) for the decay mode . In the deconfined phase, QQq melts at a certain distance and then becomes free quarks. Finally, we compare the potential of QQq with that of , and it is found that is more stable than QQqat high temperatures.

Gravitational-wave and X-ray probes of the neutron star equation of state

Neutron stars are a remarkable marriage of Einstein's theory of general relativity with nuclear physics. Their interiors harbor extreme matter that cannot be probed in the laboratory. At such high densities and pressures, their cores may consist predominantly of exotic matter such as free quarks or hyperons. Gravitational wave observations from the Laser Interferometer Gravitational-wave Observatory (LIGO) and from other interferometers, and X-ray observations from the Neutron Star Interior Composition Explorer (NICER), are beginning to pierce through the veil. These observations provide information about neutron star cores, and therefore, about the physics that makes such objects possible. In this review, we discuss what we have learned about the physics of neutron stars from gravitational wave and X-ray observations. We focus on what has been observed with certainty and what should be observable in the near future, with an eye out for the physics that these new observations will teach us.

Дискретная модель эволюции фазового пространства дробно размерных микросистем

The study of the process of changing information in microscopic systems is a rather complex and urgent scientific problem. The difficulty lies in the fact that, due to the microscopic nature of objects, it is impossible to use well-known thermodynamic methods based on the laws of large numbers. One of the possible methods for studying microscopic systems is the use of discrete Markov models with continuous time. Such models are based on the Heisenberg uncertainty principle and adequately describe the interaction between a macroscopic observer and a microscopic system at a quasi-classical level. At the same time, the use of semiclassical models makes it possible to avoid singularities, including those that cannot be eliminated, arising at small distances and high energies. In this paper, a discrete mathematical model of the phase space of an elementary particle will be used to study microscopic objects with a dimension of n=1. As a result of using the model, an original interpretation of the quark structure of hadrons was obtained. In particular, the dynamics of the functioning of quarks in the proton and neutron, the conditions for the formation of Δ resonances (Δ0, Δ+, Δ+, Δ++) are presented. The problem of the absence of free quarks (the phenomenon of confinement) is also considered. The paper considers only the first generation of quarks and the hadrons based on them. On the basis of known experimental data, numerical calculations have been carried out, showing sufficient adequacy of the model. The mathematical model of the discrete phase space, created to study the evolution of information in microscopic systems, is applicable to solving problems of elementary particle physics and can, in some cases, supplement the existing models of the quark structure of hadrons.

Static magnetic susceptibility in finite-density SUleft( 2right) lattice gauge theory

We study static magnetic susceptibility chi (T, mu ) in SU(2) lattice gauge theory with N_f = 2 light flavours of dynamical fermions at finite chemical potential mu . Using linear response theory we find that SU(2) gauge theory exhibits paramagnetic behavior in both the high-temperature deconfined regime and the low-temperature confining regime. Paramagnetic response becomes stronger at higher temperatures and larger values of the chemical potential. For our range of temperatures 0.727 le T/T_c le 2.67, the first coefficient of the expansion of chi left( T, mu right) in even powers of mu /T around mu =0 is close to that of free quarks and lies in the range (2, ldots , 5) cdot 10^{-3}. The strongest paramagnetic response is found in the diquark condensation phase at mu >mpi /2.

An Effective Model for Glueballs and Dual Superconductivity at Finite Temperature

The glueballs lead to gluon and QCD monopole condensations as by-products of color confinement. A color dielectric function G ∣ ϕ ∣ coupled with a Abelian gauge field is properly defined to mediate the glueball interactions at confining regime after spontaneous symmetry breaking (SSB) of the gauge symmetry. The particles are expected to form through the quark-gluon plasma (QGP) hadronization phase where the free quarks and gluons start clamping together to form hadrons. The QCD-like vacuum η 2 m η 2 F μ ν F μ ν , confining potential V c r , string tension σ , penetration depth λ , superconducting and normal monopole densities ( n s n n ), and the effective masses ( m η 2 and m A 2 ) will be investigated at finite temperature T . We also calculate the strong “running” coupling α s and subsequently the QCD β -function. The dual superconducting nature of the QCD vacuum will be investigated based on monopole condensation.