Particles

18 pages, 1038 KiB

Open AccessArticle

Bulk Viscous Damping of Density Oscillations in Neutron Star Mergers

by Mark Alford, Arus Harutyunyan and Armen Sedrakian

Particles 2020, 3(2), 500-517; https://doi.org/10.3390/particles3020034 - 19 Jun 2020

Cited by 30 | Viewed by 3288

In this paper, we discuss the damping of density oscillations in dense nuclear matter in the temperature range relevant to neutron star mergers. This damping is due to bulk viscosity arising from the weak interaction “Urca” processes of neutron decay and electron capture. [...] Read more.

In this paper, we discuss the damping of density oscillations in dense nuclear matter in the temperature range relevant to neutron star mergers. This damping is due to bulk viscosity arising from the weak interaction “Urca” processes of neutron decay and electron capture. The nuclear matter is modelled in the relativistic density functional approach. The bulk viscosity reaches a resonant maximum close to the neutrino trapping temperature, then drops rapidly as temperature rises into the range where neutrinos are trapped in neutron stars. We investigate the bulk viscous dissipation timescales in a post-merger object and identify regimes where these timescales are as short as the characteristic timescale ∼10 ms, and, therefore, might affect the evolution of the post-merger object. Our analysis indicates that bulk viscous damping would be important at not too high temperatures of the order of a few MeV and densities up to a few times saturation density. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2019”)

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23 pages, 575 KiB

Open AccessArticle

Chirally Improved Quark Pauli Blocking in Nuclear Matter and Applications to Quark Deconfinement in Neutron Stars

by David Blaschke, Hovik Grigorian and Gerd Röpke

Particles 2020, 3(2), 477-499; https://doi.org/10.3390/particles3020033 - 17 Jun 2020

Cited by 20 | Viewed by 2878

Abstract

The relativistic mean field (RMF) model of the nuclear matter equation of state was modified by including the effect of Pauli-blocking owing to quark exchange between the baryons. Different schemes of a chiral enhancement of the quark Pauli blocking was suggested according to [...] Read more.

The relativistic mean field (RMF) model of the nuclear matter equation of state was modified by including the effect of Pauli-blocking owing to quark exchange between the baryons. Different schemes of a chiral enhancement of the quark Pauli blocking was suggested according to the adopted density dependence of the dynamical quark mass. The resulting equations of state for the pressure are compared to the RMF model DD2 with excluded volume correction. On the basis of this comparison a density-dependent nucleon volume is extracted which parameterizes the quark Pauli blocking effect in the respective scheme of chiral enhancement. The dependence on the isospin asymmetry is investigated and the corresponding density dependent nuclear symmetry energy is obtained in fair accordance with phenomenological constraints. The deconfinement phase transition is obtained by a Maxwell construction with a quark matter phase described within a higher order NJL model. Solutions for rotating and nonrotating (hybrid) compact star sequences are obtained, which show the effect of high-mass twin compact star solutions for the rotating case. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2017”)

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21 pages, 1159 KiB

Open AccessArticle

Kinetic Equation Approach to Graphene in Strong External Fields

by Stanislav A. Smolyansky, Anatolii D. Panferov, David B. Blaschke and Narine T. Gevorgyan

Particles 2020, 3(2), 456-476; https://doi.org/10.3390/particles3020032 - 12 Jun 2020

Cited by 8 | Viewed by 2589

Abstract

The report presents the results of using the nonperturbative kinetic approach to describe the excitation of plasma oscillations in a graphene monolayer. As examples the constant electric field as well as an electric field of short high-frequency pulses are considered. The dependence of [...] Read more.

The report presents the results of using the nonperturbative kinetic approach to describe the excitation of plasma oscillations in a graphene monolayer. As examples the constant electric field as well as an electric field of short high-frequency pulses are considered. The dependence of the induced conduction and polarization currents characteristics on the pulse intensity, pulse duration, and polarization is investigated. The characteristics of secondary electromagnetic radiation resulting from the alternating currents is investigated. The nonlinear response to the external electric field characterizes graphene as an active medium. Qualitative agreement is obtained with the existing experimental result of measurements of currents in constant electric fields and radiation from graphene in the case of excitation by means of the infrared and optical pulses. Full article

(This article belongs to the Special Issue Quantum Field Theory at the Limits: From Strong Fields to Heavy Quarks)

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Graphical abstract

12 pages, 1091 KiB

Open AccessArticle

Thickness and Color Structure of Center Vortices in Gluonic SU(2) QCD

by Rudolf Golubich and Manfried Faber

Particles 2020, 3(2), 444-455; https://doi.org/10.3390/particles3020031 - 22 May 2020

Cited by 5 | Viewed by 2641

Abstract

In search for an effective model of quark confinement we study the vacuum of SU(2) quantum chromodynamic with lattice simulations using Wilson action. Assuming that center vortices are the relevant excitations causing confinement, we analyzed their physical size and their color structure. We [...] Read more.

In search for an effective model of quark confinement we study the vacuum of SU(2) quantum chromodynamic with lattice simulations using Wilson action. Assuming that center vortices are the relevant excitations causing confinement, we analyzed their physical size and their color structure. We present confirmations for a vanishing thickness of center vortices in the continuum limit and hints at their color structure. This is the first time that algorithms for the detection of thick center vortices based on non-trivial center regions has been used. Full article

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50 pages, 1120 KiB

Open AccessArticle

About Calculation of Massless and Massive Feynman Integrals

by Anatoly V. Kotikov

Particles 2020, 3(2), 394-443; https://doi.org/10.3390/particles3020030 - 7 May 2020

Cited by 6 | Viewed by 2771

Abstract

We report some results of calculations of massless and massive Feynman integrals particularly focusing on difference equations for coefficients of for their series expansions. Full article

(This article belongs to the Special Issue Quantum Field Theory at the Limits: From Strong Fields to Heavy Quarks)

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14 pages, 330 KiB

Open AccessArticle

Nonequilibrium Pion Distribution within the Zubarev Approach

by David Blaschke, Gerd Röpke, Dmitry N. Voskresensky and Vladimir G. Morozov

Particles 2020, 3(2), 380-393; https://doi.org/10.3390/particles3020029 - 3 May 2020

Cited by 6 | Viewed by 2151

Abstract

We discuss how the non-equilibrium process of pion production within the Zubarev approach of the non-equilibrium statistical operator leads to a theoretical foundation for the appearance of a non-equilibrium pion chemical potential for the pion distribution function for which there is experimental evidence [...] Read more.

We discuss how the non-equilibrium process of pion production within the Zubarev approach of the non-equilibrium statistical operator leads to a theoretical foundation for the appearance of a non-equilibrium pion chemical potential for the pion distribution function for which there is experimental evidence in experiments at the CERN LHC. Full article

(This article belongs to the Special Issue Nonequilibrium Phenomena in Strongly Correlated Systems)

16 pages, 609 KiB

Open AccessArticle

Space Dimension Renormdynamics

by Martin Bures and Nugzar Makhaldiani

Particles 2020, 3(2), 364-379; https://doi.org/10.3390/particles3020028 - 17 Apr 2020

Viewed by 2047

Abstract

We aim to construct a potential better suited for studying quarkonium spectroscopy. We put the Cornell potential into a more geometrical setting by smoothly interpolating between the observed small and large distance behaviour of the quarkonium potential. We construct two physical models, where [...] Read more.

We aim to construct a potential better suited for studying quarkonium spectroscopy. We put the Cornell potential into a more geometrical setting by smoothly interpolating between the observed small and large distance behaviour of the quarkonium potential. We construct two physical models, where the number of spatial dimensions depends on scale: one for quarkonium with Cornell potential, another for unified field theories with one compactified dimension. We construct point charge potential for different dimensions of space. The same problem is studied using operator fractal calculus. We describe the quarkonium potential in terms of the point charge potential and identify the strong coupling fine structure constant dynamics. We formulate renormdynamics of the structure constant in terms of Hamiltonian dynamics and solve the corresponding motion equations by numerical and graphical methods, we find corresponding asymptotics. Potentials of a nonlinear extension of quantum mechanics are constructed. Such potentials are ingredients of space compactification problems. Mass parameter effects are motivated and estimated. Full article

(This article belongs to the Special Issue Quantum Field Theory at the Limits: From Strong Fields to Heavy Quarks)

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9 pages, 491 KiB

Open AccessArticle

Formation of Conserved Charge at the de Sitter Space

by Valery V. Nikulin, Polina M. Petriakova and Sergey G. Rubin

Particles 2020, 3(2), 355-363; https://doi.org/10.3390/particles3020027 - 14 Apr 2020

Cited by 4 | Viewed by 2741

Abstract

The article considers a new mechanism of charge accumulation in the early Universe in theories with compact extra dimensions. The relaxation processes in the extra space metric that take place during its formation lead to the establishment of symmetrical extra space configuration. As [...] Read more.

The article considers a new mechanism of charge accumulation in the early Universe in theories with compact extra dimensions. The relaxation processes in the extra space metric that take place during its formation lead to the establishment of symmetrical extra space configuration. As a result, the initial accumulation of the number associated with the symmetry occurs. We demonstrate this mechanism using a simple example of a two-dimensional apple-like extra space metric with

U (1)

-symmetry. The conceptual idea of the mechanism can be used to develop a model for the production of the baryon or lepton number in the early Universe. Full article

(This article belongs to the Special Issue Beyond the Standard Models in Particle Physics and Cosmology)

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10 pages, 381 KiB

Open AccessEditor’s ChoiceConference Report

Critical Behavior of (2 + 1)-Dimensional QED: 1/N Expansion

by Anatoly V. Kotikov and Sofian Teber

Particles 2020, 3(2), 345-354; https://doi.org/10.3390/particles3020026 - 10 Apr 2020

Cited by 29 | Viewed by 2725

Abstract

We present recent results on dynamical chiral symmetry breaking in (2 + 1)-dimensional QED with N four-component fermions. The results of the

1 / N

expansion in the leading and next-to-leading orders were found exactly in an arbitrary nonlocal gauge. [...] Read more.

We present recent results on dynamical chiral symmetry breaking in (2 + 1)-dimensional QED with N four-component fermions. The results of the

1 / N

expansion in the leading and next-to-leading orders were found exactly in an arbitrary nonlocal gauge. Full article

(This article belongs to the Special Issue Selected Papers from “Theory of Hadronic Matter under Extreme Conditions”)

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9 pages, 288 KiB

Open AccessArticle

Cosmic Gamma Ray Constraints on the Indirect Effects of Dark Matter

by Konstantin M. Belotsky, Airat Kh. Kamaletdinov, Ekaterina S. Shlepkina and Maxim L. Solovyov

Particles 2020, 3(2), 336-344; https://doi.org/10.3390/particles3020025 - 8 Apr 2020

Cited by 5 | Viewed by 2431

Abstract

The observed anomalous excess of high-energy cosmic ray (CR) positrons is widely discussed as possible indirect evidence for dark matter (DM). However, any source of cosmic positrons is inevitably the source of gamma radiation. The least model dependent test of CR anomalies interpretation [...] Read more.

The observed anomalous excess of high-energy cosmic ray (CR) positrons is widely discussed as possible indirect evidence for dark matter (DM). However, any source of cosmic positrons is inevitably the source of gamma radiation. The least model dependent test of CR anomalies interpretation via DM particles decays (or annihilation) is connected with gamma-ray background due to gamma overproduction in such processes. In this work, we impose an observational constraint on gamma ray production from DM. Then, we study the possible suppression of gamma yield in the DM decays into identical final fermions. Such DM particles arise in the multi-component dark atom model. The influence of the interaction vertices on the gamma suppression was also considered. No essential gamma suppression effects are found. However, some minor ones are revealed. Full article

(This article belongs to the Special Issue Beyond the Standard Models in Particle Physics and Cosmology)

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16 pages, 4747 KiB

Open AccessEditor’s ChoiceArticle

Astrophysics in the Laboratory—The CBM Experiment at FAIR

by Peter Senger

Particles 2020, 3(2), 320-335; https://doi.org/10.3390/particles3020024 - 2 Apr 2020

Cited by 5 | Viewed by 3508

Abstract

The future “Facility for Antiproton and Ion Research” (FAIR) is an accelerator-based international center for fundamental and applied research, which presently is under construction in Darmstadt, Germany. An important part of the program is devoted to questions related to astrophysics, including the origin [...] Read more.

The future “Facility for Antiproton and Ion Research” (FAIR) is an accelerator-based international center for fundamental and applied research, which presently is under construction in Darmstadt, Germany. An important part of the program is devoted to questions related to astrophysics, including the origin of elements in the universe and the properties of strongly interacting matter under extreme conditions, which are relevant for our understanding of the structure of neutron stars and the dynamics of supernova explosions and neutron star mergers. The Compressed Baryonic Matter (CBM) experiment at FAIR is designed to measure promising observables in high-energy heavy-ion collisions, which are expected to be sensitive to the high-density equation-of-state (EOS) of nuclear matter and to new phases of Quantum Chromo Dynamics (QCD) matter at high densities. The CBM physics program, the relevant observables and the experimental setup will be discussed. Full article

(This article belongs to the Special Issue Selected Papers from “The Modern Physics of Compact Stars and Relativistic Gravity 2019”)

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12 pages, 363 KiB

Open AccessArticle

Gluon Propagators in QC₂D at High Baryon Density

by Vitaly Bornyakov, Andrey Kotov, Aleksandr Nikolaev and Roman Rogalyov

Particles 2020, 3(2), 308-319; https://doi.org/10.3390/particles3020023 - 1 Apr 2020

Cited by 7 | Viewed by 2953

Abstract

We study the transverse and longitudinal gluon propagators in the Landau-gauge lattice QCD with gauge group

S U (2)

at nonzero quark chemical potential and zero temperature. We show that both propagators demonstrate substantial dependence on the quark chemical potential. This [...] Read more.

We study the transverse and longitudinal gluon propagators in the Landau-gauge lattice QCD with gauge group

S U (2)

at nonzero quark chemical potential and zero temperature. We show that both propagators demonstrate substantial dependence on the quark chemical potential. This observation does not agree with earlier findings by other groups. Full article

(This article belongs to the Special Issue Selected Papers from “Theory of Hadronic Matter under Extreme Conditions”)

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30 pages, 1271 KiB

Open AccessEditor’s ChoiceArticle

A Study of the Properties of the QCD Phase Diagram in High-Energy Nuclear Collisions

by Xiaofeng Luo, Shusu Shi, Nu Xu and Yifei Zhang

Particles 2020, 3(2), 278-307; https://doi.org/10.3390/particles3020022 - 1 Apr 2020

Cited by 43 | Viewed by 5124

Abstract

With the aim of understanding the phase structure of nuclear matter created in high-energy nuclear collisions at finite baryon density, a beam energy scan program has been carried out at Relativistic Heavy Ion Collider (RHIC). In this mini-review, most recent experimental results on [...] Read more.

With the aim of understanding the phase structure of nuclear matter created in high-energy nuclear collisions at finite baryon density, a beam energy scan program has been carried out at Relativistic Heavy Ion Collider (RHIC). In this mini-review, most recent experimental results on collectivity, criticality and heavy flavor productions will be discussed. The goal here is to establish the connection between current available data and future heavy-ion collision experiments in a high baryon density region. Full article

(This article belongs to the Special Issue Relativistic and Ultrarelativistic Nuclear Collisions: Dynamics and Phase Transitions)

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6 pages, 1407 KiB

Open AccessArticle

Properties and Composition of Magnetized Nuclei

by V.N. Kondratyev

Particles 2020, 3(2), 272-277; https://doi.org/10.3390/particles3020021 - 1 Apr 2020

Cited by 4 | Viewed by 1953

Abstract

The properties and mass distribution of the ultramagnetized atomic nuclei which arise in heavy-ion collisions and magnetar crusts, during Type II supernova explosions and neutron star mergers are analyzed. For the magnetic field strength range of 0.1–10 teratesla, the Zeeman effect leads [...] Read more.

The properties and mass distribution of the ultramagnetized atomic nuclei which arise in heavy-ion collisions and magnetar crusts, during Type II supernova explosions and neutron star mergers are analyzed. For the magnetic field strength range of 0.1–10 teratesla, the Zeeman effect leads to a linear nuclear magnetic response that can be described in terms of magnetic susceptibility. Binding energies increase for open shell and decrease for closed shell nuclei. A noticeable enhancement in theyield of corresponding explosive nucleosynthesis products with antimagic numbers is predicted for iron group and r-process nuclei. Magnetic enrichment in a sampleof ⁴⁴Ti corroborate theobservational results and imply a significant increase in the quantity of the main titanium isotope, ⁴⁸Ti, in the chemical composition of galaxies. The enhancement of small mass number nuclides in the r-process peak may be due to magnetic effects. Full article

(This article belongs to the Special Issue Selected Papers from “Theory of Hadronic Matter under Extreme Conditions”)

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27 pages, 500 KiB

Open AccessEditor’s ChoiceReview

Effective Field Theories

by Andrey Grozin

Particles 2020, 3(2), 245-271; https://doi.org/10.3390/particles3020020 - 31 Mar 2020

Cited by 5 | Viewed by 2745

Abstract

This paper represents a pedagogical introduction to low-energy effective field theories. In some of them, heavy particles are “integrated out” (a typical example—the Heisenberg–Euler EFT); in some, heavy particles remain but some of their degrees of freedom are “integrated out” (Bloch–Nordsieck EFT). A [...] Read more.

This paper represents a pedagogical introduction to low-energy effective field theories. In some of them, heavy particles are “integrated out” (a typical example—the Heisenberg–Euler EFT); in some, heavy particles remain but some of their degrees of freedom are “integrated out” (Bloch–Nordsieck EFT). A large part of these lectures is, technically, in the framework of QED. QCD examples, namely decoupling of heavy flavors and HQET, are discussed only briefly. However, effective field theories of QCD are very similar to the QED case, and there are just some small technical complications: more diagrams, color factors, etc. The method of regions provides an alternative view at low-energy effective theories; this is also briefly introduced. Full article

(This article belongs to the Special Issue Quantum Field Theory at the Limits: From Strong Fields to Heavy Quarks)

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