Particles doi: 10.3390/particles4030030

Authors: Oleg Golosov Ilya Selyuzhenkov Evgeny Kashirin

The Compressed Baryonic Matter experiment (CBM) at FAIR aims to study the area of the QCD phase diagram at high net baryon densities and moderate temperatures with collisions of heavy ions at sNN=2.8–4.9 GeV. The anisotropic transverse flow is one of the most important observable phenomena in a study of the properties of matter created in such collisions. Flow measurements require the knowledge of the collision symmetry plane, which can be determined from the deflection of the collision spectators in the plane transverse to the direction of the moving ions. The CBM performance for projectile spectator symmetry plane estimation is studied with GEANT4 Monte Carlo simulations using collisions of gold ions with beam momentum of 12A GeV/c generated with the DCM-QGSM-SMM model. Different data-driven methods to extract the correction factor in flow analysis for the resolution of the spectator symmetry plane estimated with the CBM Projectile Spectator Detector are investigated.

]]>Particles doi: 10.3390/particles4030029

Authors: Fernando Domingues Amaro Elisabetta Baracchini Luigi Benussi Stefano Bianco Cesidio Capoccia Michele Caponero Gianluca Cavoto André Cortez Igor Abritta Costa Emiliano Dané Giorgio Dho Emanuele Di Marco Giulia D’Imperio Flaminia Di Giambattista Robert R. M. Gregorio Francesco Iacoangeli Herman Pessoa Lima Júnior Amaro da Silva Lopes Júnior Giovanni Maccarrone Rui Daniel Passos Mano Michela Marafini Giovanni Mazzitelli Alasdair G. McLean Andrea Messina Cristina Maria Bernardes Monteiro Rafael Antunes Nobrega Igor Fonseca Pains Emiliano Paoletti Luciano Passamonti Sandro Pelosi Fabrizio Petrucci Stefano Piacentini Davide Piccolo Daniele Pierluigi Davide Pinci Atul Prajapati Francesco Renga Rita Joana da Cruz Roque Filippo Rosatelli Andrea Russo Joaquim Marques Ferreira dos Santos Giovanna Saviano Neil Spooner Roberto Tesauro Sandro Tomassini Samuele Torelli

The CYGNO project aims at developing a high resolution Time Projection Chamber with optical readout for directional dark matter searches and solar neutrino spectroscopy. Peculiar CYGNO’s features are the 3D tracking capability provided by the combination of photomultipliers and scientific CMOS camera signals, combined with a helium-fluorine-based gas mixture at atmospheric pressure amplified by gas electron multipliers structures. In this paper, the performances achieved with CYGNO prototypes and the prospects for the upcoming underground installation at Laboratori Nazionali del Gran Sasso of a 50-L detector in fall 2021 will be discussed, together with the plans for a 1-m3 experiment. The synergy with the ERC consolidator, grant project INITIUM, aimed at realising negative ion drift operation within the CYGNO 3D optical approach, will be further illustrated.

]]>Particles doi: 10.3390/particles4030028

Authors: Ignacio Lázaro Roche

Tomography based on cosmic muon absorption is a rising technique because of its versatility and its consolidation as a geophysics tool over the past decade. It allows us to address major societal issues such as long-term stability of natural and man-made large infrastructures or sustainable underwater management. Traditionally, muon trackers consist of hodoscopes or multilayer detectors. For applications with challenging available volumes or the wide field of view required, a thin time projection chamber (TPC) associated with a Micromegas readout plane can provide a good tradeoff between compactness and performance. This paper details the design of such a TPC aiming at maximizing primary signal and minimizing track reconstruction artifacts. The results of the measurements performed during a case study addressing the aforementioned applications are discussed. The current works lines and perspectives of the project are also presented.

]]>Particles doi: 10.3390/particles4020027

Authors: Luca Nanni

In this article, the general solution of the tachyonic Klein–Gordon equation is obtained as a Fourier integral performed on a suitable path in the complex ω-plane. In particular, it is proved that this solution does not contain any superluminal components under the given boundary conditions. On the basis of this result, we infer that all possible spacelike wave equations describe the dynamics of subluminal particles endowed with imaginary mass. This result is validated for the Chodos equation, used to describe the hypothetical superluminal behaviour of the neutrino. In this specific framework, it is proved that the wave packet propagates in spacetime with subluminal group velocities and that it behaves as a localized wave for sufficiently small energies.

]]>Particles doi: 10.3390/particles4020026

Authors: Mario Panelli Davide Morfei Beniamino Milo Francesco Antonio D’Aniello Francesco Battista

Hall Effect Thrusters (HETs) are nowadays widely used for satellite applications because of their efficiency and robustness compared to other electric propulsion devices. Computational modelling of plasma in HETs is interesting for several reasons: it can be used to predict thrusters’ operative life; moreover, it provides a better understanding of the physical behaviour of this device and can be used to optimize the next generation of thrusters. In this work, the discharge within the accelerating channel and near-plume of HETs has been modelled by means of an axisymmetric hybrid approach: a set of fluid equations for electrons has been solved to get electron temperatures, plasma potential and the discharge current, whereas a Particle-In-Cell (PIC) sub-model has been developed to capture the behaviour of neutrals and ions. A two-region electron mobility model has been incorporated. It includes electron–neutral/ion collisions and uses empirical constants, that vary as a continuous function of axial coordinates, to take into account electron–wall collisions and Bohm diffusion/SEE effects. An SPT-100 thruster has been selected for the verification of the model because of the availability of reliable numerical and experimental data. The results of the presented simulations show that the code is able to describe plasma discharge reproducing, with consistency, the physics within the accelerating channel of HETs. A small discrepancy in the experimental magnitude of ions’ expansion, due probably to boundary condition effects, has been found.

]]>Particles doi: 10.3390/particles4020025

Authors: Oleksii Lubynets Ilya Selyuzhenkov Viktor Klochkov

We present the current status of the performance studies of Λ hyperon directed flow measurement with the CBM experiment at the future FAIR facility in Darmstadt. Kalman Filter mathematics is used to reconstruct Λ→pπ− weak decay kinematics, while the Particle Finder Simple package is used to optimize criteria for Λ hyperon candidate selection. Directed flow of Λ hyperons is studied as a function of rapidity, transverse momentum and collision centrality. The effects on flow measurement due to non-uniformity of the CBM detector response in the azimuthal angle, transverse momentum and rapidity are corrected using the QnTools analysis framework.

]]>Particles doi: 10.3390/particles4020024

Authors: Petr Parfenov Dim Idrisov Vinh Ba Luong Arkadiy Taranenko

The size and evolution of the matter created in relativistic heavy-ion collisions strongly depend on collision geometry, defined by the impact parameter. However, the impact parameter cannot be measured directly in an experiment but might be inferred from final state observables using the centrality procedure. We present the procedure of centrality determination for the Multi-Purpose Detector (MPD) at the NICA collider and its performance using the multiplicity of produced charged particles at midrapidity. The validity of the procedure is assessed using the simulated data for Au + Au collisions at sNN = 4–11 GeV.

]]>Particles doi: 10.3390/particles4020023

Authors: Pierluigi Belli Rita Bernabei Vincenzo Caracciolo

This paper reviews the main experimental techniques and the most significant results in the searches for the 2ϵ, ϵβ+ and 2β+ decay modes. Efforts related to the study of these decay modes are important, since they can potentially offer complementary information with respect to the cases of 2β− decays, which allow a better constraint of models for the nuclear structure calculations. Some positive results that have been claimed will be mentioned, and some new perspectives will be addressed shortly.

]]>Particles doi: 10.3390/particles4020022

Authors: Vadim Volkov Marina Golubeva Fedor Guber Alexander Ivashkin Nikolay Karpushkin Sergey Morozov Sultan Musin Alexander Strizhak

Two approaches related to the centrality determination in heavy-ion Multi-Purpose Detector (MPD) experiments, using charge-particles multiplicity in Time Projection Chamber (TPC) and the energy deposition in Forward Hadron Calorimeter (FHCal) are discussed. The main features of the FHCal are the fine transverse segmentation and the beam holes in the center of the calorimeters. Leaking the heavy non-interacting fragments (spectators) leads to ambiguity in the dependence of energy deposition in the FHCal on the collision centrality. However, the calorimeter transverse segmentation allows one to measure the energy distributions in each of the FHCal modules and to construct combined observables to resolve the problems associated with the beam hole. The comparison of these approaches in the collision centrality measurements is discussed.

]]>Particles doi: 10.3390/particles4020021

Authors: Aleksandr Svetlichnyi Roman Nepeyvoda Igor Pshenichnov

One of the common methods to measure the centrality of nucleus-nucleus collision events consists of detecting forward spectator neutrons. Because of non-monotonic dependence of neutron numbers on centrality, other characteristics of spectator matter in 197Au–197Au collisions at NICA must be considered to improve the centrality determination. The numbers of spectator deuterons and α-particles and the forward–backward asymmetry of the numbers of free spectator nucleons were calculated with the Abrasion–Ablation Monte Carlo for Colliders (AAMCC) model as functions of event centrality. It was shown that the number of charged fragments per spectator nucleon decreases monotonically with an increase of the impact parameter, and thus can be used to estimate the collision centrality. The conditional probabilities that a given event with specific spectator characteristics belongs to a certain centrality class were calculated by means of AAMCC. Such probabilities can be used as an input to Bayesian or other machine-learning approaches to centrality determination in 197Au–197Au collisions.

]]>Particles doi: 10.3390/particles4020020

Authors: Peter Senger

The “Facility for Antiproton and Ion Research” (FAIR) in Darmstadt, Germany, and the “Nuclotron-based Ion Collider Facility” (NICA) in Dubna, Russia, are two accelerator centers under construction. FAIR will provide beams and experimental setups to perform forefront research in hadron, nuclear, atomic, and plasma physics, as well as in radiation biology and material science. At NICA, a unique research program on nuclear matter and spin physics will be conducted. Both facilities will execute experiments to explore the properties of QCD matter at neutron star core densities, in order to study the high-density equation of state, and to shed light on the quark degrees-of-freedom emerging in QCD matter at high densities. The research programs will be performed at FAIR with the CBM experiment, and at NICA with the MPD setup at the collider, and with the BM@N experiment at the Nuclotron. These three experiments are complementary, with respect to the beam energy. The physics programs and the relevant experimental observables will be discussed.

]]>Particles doi: 10.3390/particles4020019

Authors: Anna Senger Peter Senger

The Compressed Baryonic Matter (CBM) experiment at the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt is designed to investigate the properties of high-density QCD matter with multi-differential measurements of hadrons and leptons, including rare probes such as multi-strange anti-hyperons and charmed particles. The research program covers the study of the high-density equation-of-state of nuclear matter and the exploration of the QCD phase diagram at large baryon chemical potentials, including the search for quark matter and the critical endpoint of a hypothetical 1st order phase transition. The CBM setup comprises detector systems for the identification of charged hadrons, electrons, and muons; for the determination of collision centrality and the orientation of the reaction plane; and a free-streaming data read-out and acquisition system, which allows online reconstruction and selection of events up to reaction rates of 10 MHz. In this article, emphasis is placed on the measurement of muon pairs in Au-Au collisions at FAIR beam energies, which are unique probes used to determine the temperature of the fireball, and hence to search for a caloric curve of QCD matter. Simultaneously, the subthreshold production of charmonium can be studied via its dimuon decay in order to shed light on the microscopic structure of QCD matter at high baryon densities. The CBM setup with focus on dimuon measurements and the results of the corresponding physics performance studies will be presented.

]]>Particles doi: 10.3390/particles4020018

Authors: Omar Benhar

Experimental studies of hypernuclear dynamics, besides being essential for the understanding of strong interactions in the strange sector, have important astrophysical implications. The observation of neutron stars with masses exceeding two solar masses poses a serious challenge to the models of hyperon dynamics in dense nuclear matter, many of which predict a maximum mass incompatible with the data. In this paper, it is argued that valuable new insight can be gained from the forthcoming extension of the experimental studies of kaon electro production from nuclei to include the 208Pb(e,e′K+)Λ208Tl process. A comprehensive framework for the description of kaon electro production, based on factorization of the nuclear cross section and the formalism of the nuclear many-body theory, is outlined. This approach highlights the connection between the kaon production and proton knockout reactions, which will allow us to exploit the available 208Pb(e,e′p)207Tl data to achieve a largely model-independent analysis of the measured cross section.

]]>Particles doi: 10.3390/particles4020017

Authors: Dmitry Zinchenko Eduard Nikonov Veronika Vasendina Alexander Zinchenko

As a part of the future upgrade program of the Multi-Purpose Detector (MPD) experiment at the Nuclotron-Based Ion Collider Facility (NICA) complex, an Inner Tracking System (ITS) made of Monolitic Active Pixel Sensors (MAPSs) is proposed between the beam pipe and the Time Projection Chamber (TPC). It is expected that the new detector will enhance the experimental potential for the reconstruction of short-lived particles—in particular, those containing the open charm particle. To study the detector performance and select its best configuration, a track reconstruction approach based on a constrained combinatorial search was developed and implemented as a software toolkit called Vector Finder. This paper describes the proposed approach and demonstrates its characteristics for primary and secondary track finding in ITS, ITS-to-TPC track matching and hyperon reconstruction within the MPD software framework. The results were obtained on a set of simulated central gold–gold collision events at sNN=9 GeV with an average multiplicity of ∼1000 charged particles in the detector acceptance produced with the Ultra-Relativistic Quantum Molecular Dynamics (UrQMD) generator.

]]>Particles doi: 10.3390/particles4020016

Authors: Alexander Zinchenko

Study of the strangeness production in heavy-ion collisions is one of the most important parts of the physics program of the MPD experiment at the NICA collider. Therefore, the problem of a reliable and efficient reconstruction of strange objects should be addressed with a high priority during the preparation to the experiment. The paper describes the approach to this task which was developed and implemented as a part of the MPD software. Some results of its application during the detector Monte Carlo feasibility studies are presented.

]]>Particles doi: 10.3390/particles4020015

Authors: Rico Zöllner Burkhard Kämpfer

A holographic model of probe quarkonia is presented, where the dynamical gravity–dilaton background was adjusted to the thermodynamics of 2 + 1 flavor QCD with physical quark masses. The quarkonia action was modified to account for the systematic study of the heavy-quark mass dependence. We focused on the J/ψ and Υ spectral functions and related our model to heavy quarkonia formation as a special aspect of hadron phenomenology in heavy-ion collisions at LHC.

]]>Particles doi: 10.3390/particles4020014

Authors: Petr Parfenov Dim Idrisov Vinh Ba Luong Nikolay Geraksiev Anton Truttse Alexander Demanov

The primary scientific mission of the Multi-Purpose Detector (MPD) at the accelerator Nuclotron-based Ion Collider facility (NICA) (Dubna) is to investigate the properties of strongly interacting matter at high net-baryon densities. The goal of this work is to study the performance of the MPD detector for directed and elliptic flow measurements of identified hadrons by using the realistic Monte Carlo simulations of heavy-ion collisions at energies sNN = 4.5 − 11 GeV.

]]>Particles doi: 10.3390/particles4020013

Authors: Irina Dymnikova

We present a systematic review of the basic features that were adopted for different electron models and show, in a brief overview, that, for electromagnetic spinning solitons in nonlinear electrodynamics minimally coupled to gravity (NED-GR), all of these features follow directly from NED-GR dynamical equations as model-independent generic features. Regular spherically symmetric solutions of NED-GR equations that describe electrically charged objects have obligatory de Sitter center due to the algebraic structure of stress–energy tensors for electromagnetic fields. By the Gürses-Gürsey formalism, which includes the Newman–Janis algorithm, they are transformed to axially symmetric solutions that describe regular spinning objects asymptotically Kerr–Newman for a distant observer, with the gyromagnetic ratio g=2. Their masses are determined by the electromagnetic density, related to the interior de Sitter vacuum and to the breaking of spacetime symmetry from the de Sitter group. De Sitter center transforms to the de Sitter vacuum disk, which has properties of a perfect conductor and ideal diamagnetic. The ring singularity of the Kerr–Newman geometry is replaced with the superconducting current, which serves as the non-dissipative source for exterior fields and source of the intrinsic magnetic momentum for any electrically charged spinning NED-GR object. Electromagnetic spinning soliton with the electron parameters can shed some light on appearance of a minimal length scale in the annihilation reaction e+e−→γγ(γ).

]]>Particles doi: 10.3390/particles4020012

Authors: Claudia Moreno Juan Carlos Degollado Darío Núñez Carlos Rodríguez-Leal

We derive a set of coupled equations for the gravitational and electromagnetic perturbation in the Reissner–Nordström geometry using the Newman–Penrose formalism. We show that the information of the physical gravitational signal is contained in the Weyl scalar function Ψ4, as is well known, but for the electromagnetic signal, the information is encoded in the function χ, which relates the perturbations of the radiative Maxwell scalars φ2 and the Weyl scalar Ψ3. In deriving the perturbation equations, we do not impose any gauge condition and as a limiting case, our analysis contains previously obtained results, for instance, those from Chandrashekhar’s book. In our analysis, we also include the sources for the perturbations and focus on a dust-like charged fluid distribution falling radially into the black hole. Finally, by writing the functions on the basis of spin-weighted spherical harmonics and the Reissner–Nordström spacetime in Kerr–Schild type coordinates, a hyperbolic system of coupled partial differential equations is presented and numerically solved. In this way, we completely solve a system that generates a gravitational signal as well as an electromagnetic/gravitational one, which sets the basis to find correlations between them and thus facilitates gravitational wave detection via electromagnetic signals.

]]>Particles doi: 10.3390/particles4010011

Authors: Rudolf Golubich Manfried Faber

New analysis regarding the structure of center vortices is presented: Using data from gluonic SU(2) lattice simulation with Wilson action, a correlation of fluctuations in color space to the curvature of vortex fluxes was found. Finite size effects of the S2-homogeneity hint at color homogeneous regions on the vortex surface.

]]>Particles doi: 10.3390/particles4010010

Authors: R. Sahu V. K. B. Kota T. S. Kosmas

Detection rates for the elastic and inelastic scattering of weakly interacting massive particles (WIMPs) off 23Na are calculated within the framework of Deformed Shell Model (DSM) based on Hartree-Fock states. At first, the spectroscopic properties of the detector nucleus, like energy spectra and magnetic moments, are evaluated and compared with experimental data. Following the good agreement of these results, DSM wave functions are used for obtaining elastic and inelastic spin structure functions, nuclear structure coefficients and so forth for the WIMP-23Na scattering. Then, the event rates are also computed with a given set of supersymmetric parameters. In the same manner, using DSM wavefunctions, nuclear structure coefficients and event rates for elastic scattering of WIMPs from 40Ar are also obtained. These results for event rates and also for annual modulation will be useful for the ongoing and future WIMP detection experiments involving detector materials with 23Na and 40Ar nuclei.

]]>Particles doi: 10.3390/particles4010009

Authors: Toshitaka Tatsumi Hiroaki Abuki

Transport properties of dense quark matter are discussed in the strong magnetic field, B. B dependence as well as density dependence of the Hall conductivity is discussed, based on the microscopic Kubo formula. We took into account the possibility of the inhomogeneous chiral phase at moderate densities, where anomalous Hall effect is intrinsic and resembles the one in Weyl semimetals in condensed matter physics. Some theoretical aspects inherent in anomalous Hall effect are also discussed.

]]>Particles doi: 10.3390/particles4010008

Authors: Evgeny Kryshen Dmitry Ivanishchev Dmitry Kotov Mikhail Malaev Victor Riabov Yuriy Ryabov

Spectra of thermal photons carry important information on the temperature of the hot and dense medium produced in heavy ion collisions. Photons can be measured via their conversion into electron-positron pairs in the detector material. In this contribution, challenges in the photon reconstruction are discussed and feasibility studies on photon conversion measurements in the future multipurpose detector (MPD) experiment at NICA are presented. The obtained results indicate good prospects for thermal photon measurements.

]]>Particles doi: 10.3390/particles4010007

Authors: Armen Sedrakian

Particles (ISSN 2571-712X), which is a peer-reviewed, open access journal launched in 2018, has now reached a significant milestone—the 100th paper has been published [...]

]]>Particles doi: 10.3390/particles4010006

Authors: Manjunath Omana Kuttan Jan Steinheimer Kai Zhou Andreas Redelbach Horst Stoecker

In this talk we presented a novel technique, based on Deep Learning, to determine the impact parameter of nuclear collisions at the CBM experiment. PointNet based Deep Learning models are trained on UrQMD followed by CBMRoot simulations of Au+Au collisions at 10 AGeV to reconstruct the impact parameter of collisions from raw experimental data such as hits of the particles in the detector planes, tracks reconstructed from the hits or their combinations. The PointNet models can perform fast, accurate, event-by-event impact parameter determination in heavy ion collision experiments. They are shown to outperform a simple model which maps the track multiplicity to the impact parameter. While conventional methods for centrality classification merely provide an expected impact parameter distribution for a given centrality class, the PointNet models predict the impact parameter from 2–14 fm on an event-by-event basis with a mean error of −0.33 to 0.22 fm.

]]>Particles doi: 10.3390/particles4010005

Authors: Particles Editorial Office Particles Editorial Office

Peer review is the driving force of journal development, and reviewers are gatekeepers who ensure that Particles maintains its standards for the high quality of its published papers [...]

]]>Particles doi: 10.3390/particles4010004

Authors: Gevorg Hajyan

The integral parameters (mass, radius) of hot proto-quark stars that are formed in supernova explosion are studied. We use the MIT bag model to determine the pressure of up-down and strage quark matter at finite temperature and in the regime where neutrinos are trapped. It is shown that such stars are heated to temperatures of the order of tens of MeV. The maximum possible values of the central temperatures of these stars are determined. It is shown that the energy of neutrinos that are emitted from proto-quark stars is of the order of 250÷300 MeV. Once formed, the proto-quark stars cool by neutrino emission, which leads to a decrease in the mass of these stars by about 0.16–0.25 M⊙ for stars with the rest masses that are in the range Mb=1.22−1.62&nbsp;M⊙.

]]>Particles doi: 10.3390/particles4010003

Authors: Dmitry Ivanishchev Dmitry Kotov Mikhail Malaev Victor Riabov Yury Ryabov

The study of hadronic resonance production is an essential part of the physical programs of many heavy-ion experiments. Detailed measurement of the resonance properties is also foreseen in the future Multi-Purpose Detector (MPD) experiment at the NICA collider. In this report, we focus on the experimental challenges for the reconstruction of resonances in heavy-ion experiments and examine the MPD capabilities for the reconstruction of &rho;(770)0, K*(892)0,&plusmn;, &phi;(1020), &Lambda;(1520), &Sigma;(1385)&plusmn; and &Xi;(1530)0.

]]>Particles doi: 10.3390/particles4010002

Authors: Lior Shamir

Observations of non-random distribution of galaxies with opposite spin directions have recently attracted considerable attention. Here, a method for identifying cosine-dependence in a dataset of galaxies annotated by their spin directions is described in the light of different aspects that can impact the statistical analysis of the data. These aspects include the presence of duplicate objects in a dataset, errors in the galaxy annotation process, and non-random distribution of the asymmetry that does not necessarily form a dipole or quadrupole axes. The results show that duplicate objects in the dataset can artificially increase the likelihood of cosine dependence detected in the data, but a very high number of duplicate objects is required to lead to a false detection of an axis. Inaccuracy in galaxy annotations has relatively minor impact on the identification of cosine dependence when the error is randomly distributed between clockwise and counterclockwise galaxies. However, when the error is not random, even a small bias of 1% leads to a statistically significant cosine dependence that peaks at the celestial pole. Experiments with artificial datasets in which the distribution was not random showed strong cosine dependence even when the data did not form a full dipole axis alignment. The analysis when using the unmodified data shows asymmetry profile similar to the profile shown in multiple previous studies using several different telescopes.

]]>Particles doi: 10.3390/particles4010001

Authors: Victor Riabov

Hadronic resonances play an important role in the study of the physics of heavy-ion collisions. In these proceedings, we discuss how the resonances can probe the reaction dynamics, the strangeness production and the properties of the hadronic phase in heavy-ion collisions at center-of-mass energies of sNN = 4&ndash;11 GeV. The resonance properties predicted by the general-purpose event generators are found to be very sensitive to the properties and space-time evolution of the medium produced in heavy-ion collisions.

]]>Particles doi: 10.3390/particles3040047

Authors: Dmitri V. Kirpichnikov Valery E. Lyubovitskij Alexey S. Zhevlakov

We discuss constraints on soft CP-violating couplings of axion-like particles with photon and fermions by using data on electric dipole moments of standard model particles. In particular, for the axion-like particle (ALP) leptophilic scenario, we derive bounds on CP-odd ALP-photon-photon coupling from data of the ACME collaboration on electron EDM. We also discuss prospects of the storage ring experiment to constrain the ALP&ndash;photon&ndash;photon coupling from data on proton EDM for the simplified hadrophilic interactions of ALP. The resulting constraints from experimental bounds on the muon and neutron EDMs are weak. We set constraint on the CP-odd ALP coupling with electron and derive bounds on combinations of coupling constants, which involve soft CP-violating terms.

]]>Particles doi: 10.3390/particles3040046

Authors: Luca Riz Francesco Pederiva Diego Lonardoni Stefano Gandolfi

The spin susceptibility in pure neutron matter is computed from auxiliary field diffusion Monte Carlo calculations over a wide range of densities. The calculations are performed for different spin asymmetries, while using twist-averaged boundary conditions to reduce finite-size effects. The employed nuclear interactions include both the phenomenological Argonne AV8&prime; + UIX potential and local interactions that are derived from chiral effective field theory up to next-to-next-to-leading order.

]]>Particles doi: 10.3390/particles3040045

Authors: Stefanos Tsiopelas Violetta Sagun

We study the thermal evolution of neutron stars described within the equation of state with induced surface tension (IST) that reproduces properties of normal nuclear matter, fulfills the proton flow constraint, provides a high-quality description of hadron multiplicities created during the nuclear-nuclear collision experiments, and it is equally compatible with the constraints from astrophysical observations and the GW170817 event. The model features strong direct Urca processes for the stars above 1.91M⊙. The IST equation of state shows very good agreement with the available cooling data, even without introducing nuclear pairing. We also analysed the effect of the singlet proton/neutron and triplet neutron pairing on the cooling of neutron stars of different mass. We show that the description of the compact object in the center of the Cassiopeia A does not necessarily require an inclusion of neutron superfluidity and/or proton superconductivity. Our results indicate that data of Cassiopeia A can be adequately well reproduced by a 1.66M⊙ star with an atmosphere of light elements. Moreover, the IST EoS reproduces each of the observational datasets for the surface temperature of Cassiopeia A either by a rapidly cooling &sim;1.955M⊙ star with paired and unpaired matter or by a 1.91M⊙ star with the inclusion of neutron and proton pairings in the singlet channel.

]]>Particles doi: 10.3390/particles3040044

Authors: Ivan Dadić Dubravko Klabučar Domagoj Kuić

Within the finite-time-path out-of-equilibrium quantum field theory (QFT), we calculate direct photon emission from early stages of heavy ion collisions, from a narrow window, in which uncertainty relations are still important and they provide a new mechanism for production of photons. The basic difference with respect to earlier calculations, leading to diverging results, is that we use renormalized QED of quarks and photons. Our result is a finite contribution that is consistent with uncertainty relations.

]]>Particles doi: 10.3390/particles3040043

Authors: Vivek Baruah Thapa Monika Sinha Jia Jie Li Armen Sedrakian

We construct a new equation of state for the baryonic matter under an intense magnetic field within the framework of covariant density functional theory. The composition of matter includes hyperons as well as &Delta;-resonances. The extension of the nucleonic functional to the hypernuclear sector is constrained by the experimental data on &Lambda; and &Xi;-hypernuclei. We find that the equation of state stiffens with the inclusion of the magnetic field, which increases the maximum mass of neutron star compared to the non-magnetic case. In addition, the strangeness fraction in the matter is enhanced. Several observables, like the Dirac effective mass, particle abundances, etc. show typical oscillatory behavior as a function of the magnetic field and/or density which is traced back to the occupation pattern of Landau levels.

]]>Particles doi: 10.3390/particles3030042

Authors: Brandon Mattingly Abinash Kar Matthew Gorban William Julius Cooper K. Watson M.D. Ali Andrew Baas Caleb Elmore Jeffrey S. Lee Bahram Shakerin Eric W. Davis Gerald B. Cleaver

A process for using curvature invariants is applied to evaluate the accelerating Nat&aacute;rio warp drive. Curvature invariants are independent of coordinate bases and plotting the invariants is free of coordinate mapping distortions. While previous works focus mainly on the mathematical description of the warp bubble, plotting curvature invariants provides a novel pathway to investigate the Nat&aacute;rio spacetime and its characteristics. For warp drive spacetimes, there are four independent curvature invariants the Ricci scalar, r1, r2, and w2. The invariant plots demonstrate how each curvature invariant evolves over the parameters of time, acceleration, skin depth and radius of the warp bubble. They show that the Ricci scalar has the greatest impact of the invariants on the surrounding spacetime. They also reveal key features of the Nat&aacute;rio warp bubble such as a flat harbor in the center of it, a dynamic wake, and the internal structures of the warp bubble.

]]>Particles doi: 10.3390/particles3030041

Authors: Ulrich D. Jentschura

The hypothesis of Lorentz violation in the neutrino sector has intrigued scientists for the last two to three decades. A number of theoretical arguments support the emergence of such violations, first and foremost for neutrinos, which constitute the &ldquo;most elusive&rdquo; and &ldquo;least interacting&rdquo; particles known to mankind. It is of obvious interest to place stringent bounds on the Lorentz-violating parameters in the neutrino sector. In the past, the most stringent bounds have been placed by calculating the probability of neutrino decay into a lepton pair, a process made kinematically feasible by Lorentz violation in the neutrino sector, above a certain threshold. However, even more stringent bounds can be placed on the Lorentz-violating parameters if one takes into account, additionally, the possibility of neutrino splitting, i.e., of neutrino decay into a neutrino of lower energy, accompanied by &ldquo;neutrino-pair Čerenkov radiation.&rdquo; This process has a negligible threshold and can be used to improve the bounds on Lorentz-violating parameters in the neutrino sector. Finally, we take the opportunity to discuss the relation of Lorentz and gauge symmetry breaking, with a special emphasis on the theoretical models employed in our calculations.

]]>Particles doi: 10.3390/particles3030040

Authors: Prasanta Char Silvia Traversi Giuseppe Pagliara

We present a Bayesian analysis on the equation of state of neutron stars based on a class of relativistic mean field models. The priors on the equation of state are related to the properties of nuclear matter at saturation and the posteriors are obtained through the Bayesian procedure by exploiting recent astrophysical constraints on the mass&ndash;radius relations of neutron stars. We find indications of a tension (within the adopted model) between the prior on the nuclear incompressibility and its posterior which in turn seems to suggest a possible phase transition at about twice saturation density to a phase where the nucleon effective mass is strongly reduced. A possible relation with the chiral phase transition in dense matter is also discussed.

]]>Particles doi: 10.3390/particles3030039

Authors: A. S. Gevorkyan

The article formulates the classical three-body problem in conformal-Euclidean space (Riemannian manifold), and its equivalence to the Newton three-body problem is mathematically rigorously proved. It is shown that a curved space with a local coordinate system allows us to detect new hidden symmetries of the internal motion of a dynamical system, which allows us to reduce the three-body problem to the 6th order system. A new approach makes the system of geodesic equations with respect to the evolution parameter of a dynamical system (internal time) fundamentally irreversible. To describe the motion of three-body system in different random environments, the corresponding stochastic differential equations (SDEs) are obtained. Using these SDEs, Fokker-Planck-type equations are obtained that describe the joint probability distributions of geodesic flows in phase and configuration spaces. The paper also formulates the quantum three-body problem in conformal-Euclidean space. In particular, the corresponding wave equations have been obtained for studying the three-body bound states, as well as for investigating multichannel quantum scattering in the framework of the concept of internal time. This allows us to solve the extremely important quantum-classical correspondence problem for dynamical Poincar&eacute; systems.

]]>Particles doi: 10.3390/particles3030038

Authors: Tatiana A. Khantuleva Victor M. Kats

In different areas of mechanics, highly non-equilibrium processes are accompanied by self-organization of various type turbulent structures and localized inhomogeneities at intermediate scale between macro and micro levels. In order to describe the self-organization of the new dynamic structures on the mesoscale, a new problem formulation based on the results of non-equilibrium statistical mechanics, control theory of adaptive systems, and theory of a special type nonlinear operator sets is proposed. Determination of the turbulent structure parameters through constraints imposed on the system in the form of nonlinear functionals is an inverse problem similar to problems on spectra in quantum mechanics. Like in quantum mechanics, the bounded system in response to impact forms a discrete spectrum of the turbulent structure sizes and lifetimes which goes into continuous spectrum close-to-equilibrium. The proposed description of the structure evolution on the intermediate scale level which is valid far from thermodynamic equilibrium bridges the gap between macroscopic theories and quantum mechanics and affirms the unity of the physical laws of nature.

]]>Particles doi: 10.3390/particles3030037

Authors: Priidik Gallagher Stefan Groote Maria Naeem

The propagator of a gauge boson, like the massless photon or the massive vector bosons W&plusmn; and Z of the electroweak theory, can be derived in two different ways, namely via Green&rsquo;s functions (semi-classical approach) or via the vacuum expectation value of the time-ordered product of the field operators (field theoretical approach). Comparing the semi-classical with the field theoretical approach, the central tensorial object can be defined as the gauge boson projector, directly related to the completeness relation for the complete set of polarisation four-vectors. In this paper we explain the relation for this projector to different cases of the R&xi; gauge and explain why the unitary gauge is the default gauge for massive gauge bosons.

]]>Particles doi: 10.3390/particles3030036

Authors: Artyom Astashenok Sergey Odintsov

We present a brief review of general results about non-rotating neutron stars in simple R 2 gravity and its extension with a scalar axion field. Modified Einstein equations are presented for metrics in isotropical coordinates. The mass&ndash;radius relation, mass profile and dependence of mass from central density on various equations of state are given in comparison to general relativity.

]]>Particles doi: 10.3390/particles3030035

Authors: Dragan Lukman Mickael Komendyak Norma Susana Mankoč Borštnik

The internal degrees of freedom of fermions are in the spin-charge-family theory described by the Clifford algebra objects, which are superposition of an odd number of &gamma; a &rsquo;s. Arranged into irreducible representations of &ldquo;eigenvectors&rdquo; of the Cartan subalgebra of the Lorentz algebra S a b ( = i 2 &gamma; a &gamma; b | a &ne; b ) these objects form 2 d 2 &minus; 1 families with 2 d 2 &minus; 1 family members each. Family members of each family offer the description of all the observed quarks and leptons and antiquarks and antileptons, appearing in families. Families are reachable by S &tilde; a b = 1 2 &gamma; &tilde; a &gamma; &tilde; b | a &ne; b . Creation operators, carrying the family member and family quantum numbers form the basis vectors. The action of the operators &gamma; a &rsquo;s, S a b , &gamma; &tilde; a &rsquo;s and S &tilde; a b , applying on the basis vectors, manifests as matrices. In this paper the basis vectors in d = ( 3 + 1 ) Clifford space are discussed, chosen in a way that the matrix representations of &gamma; a and of S a b coincide for each family quantum number, determined by S &tilde; a b , with the Dirac matrices. The appearance of charges in Clifford space is discussed by embedding d = ( 3 + 1 ) space into d = ( 5 + 1 ) -dimensional space. The achievements and predictions of the spin-charge-family theory is also shortly presented.

]]>Particles doi: 10.3390/particles3020034

Authors: Mark Alford Arus Harutyunyan Armen Sedrakian

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 &ldquo;Urca&rdquo; 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 &sim;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.

]]>Particles doi: 10.3390/particles3020033

Authors: David Blaschke Hovik Grigorian Gerd Röpke

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.

]]>Particles doi: 10.3390/particles3020032

Authors: Stanislav A. Smolyansky Anatolii D. Panferov David B. Blaschke Narine T. Gevorgyan

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.

]]>Particles doi: 10.3390/particles3020031

Authors: Rudolf Golubich Manfried Faber

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.

]]>Particles doi: 10.3390/particles3020030

Authors: Anatoly V. Kotikov

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

]]>Particles doi: 10.3390/particles3020029

Authors: David Blaschke Gerd Röpke Dmitry N. Voskresensky Vladimir G. Morozov

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.

]]>Particles doi: 10.3390/particles3020028

Authors: Martin Bures Nugzar Makhaldiani

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.

]]>Particles doi: 10.3390/particles3020027

Authors: Valery V. Nikulin Polina M. Petriakova Sergey G. Rubin

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.

]]>Particles doi: 10.3390/particles3020026

Authors: Anatoly V. Kotikov Sofian Teber

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.

]]>Particles doi: 10.3390/particles3020025

Authors: Konstantin M. Belotsky Airat Kh. Kamaletdinov Ekaterina S. Shlepkina Maxim L. Solovyov

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.

]]>Particles doi: 10.3390/particles3020024

Authors: Peter Senger

The future &ldquo;Facility for Antiproton and Ion Research&rdquo; (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.

]]>Particles doi: 10.3390/particles3020023

Authors: Vitaly Bornyakov Andrey Kotov Aleksandr Nikolaev Roman Rogalyov

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.

]]>Particles doi: 10.3390/particles3020022

Authors: Xiaofeng Luo Shusu Shi Nu Xu Yifei Zhang

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.

]]>Particles doi: 10.3390/particles3020021

Authors: V.N. Kondratyev

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&ndash;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.

]]>Particles doi: 10.3390/particles3020020

Authors: Andrey Grozin

This paper represents a pedagogical introduction to low-energy effective field theories. In some of them, heavy particles are &ldquo;integrated out&rdquo; (a typical example&mdash;the Heisenberg&ndash;Euler EFT); in some, heavy particles remain but some of their degrees of freedom are &ldquo;integrated out&rdquo; (Bloch&ndash;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.

]]>Particles doi: 10.3390/particles3010019

Authors: Rudolf N. Faustov Vladimir O. Galkin

Masses of heavy baryons are calculated in the framework of the relativistic quark-diquark picture and QCD. The obtained results are in good agreement with available experimental data including recent measurements by the LHCb Collaboration. Possible quantum numbers of excited heavy baryon states are discussed.

]]>Particles doi: 10.3390/particles3010018

Authors: Leonhard Klar

Up to date, quantum electrodynamics (QED) is the most precisely tested quantum field theory. Nevertheless, particularly in the high-intensity regime it predicts various phenomena that so far have not directly been accessible in all-optical experiments, such as photon-photon scattering phenomena induced by quantum vacuum fluctuations. Here, we focus on all-optical signatures of quantum vacuum effects accessible in the high-intensity regime of electromagnetic fields. We present an experimental setup giving rise to signal photons distinguishable from the background. This configuration is based on two optical pulsed petawatt lasers: one generates a narrow but high-intensity scattering center to be probed by the other one. We calculate the differential number of signal photons attainable with this field configuration analytically and compare it with the background of the driving laser beams.

]]>Particles doi: 10.3390/particles3010017

Authors: Rudolf N. Faustov Vladimir O. Galkin

Semileptonic and rare semileptonic decays of heavy baryons are studied in the framework of the relativistic quark model based on the quark-diquark picture, quasipotential approach, and quantum chromodynamics (QCD). The form factors parametrizing the matrix elements of the weak transitions are calculated in the whole accessible kinematical range with the comprehensive account of the relativistic effects. The obtained results for the branching ratios and other observables agree well with the available experimental data.

]]>Particles doi: 10.3390/particles3010016

Authors: Mikhail A. Ivanov Jürgen G. Körner Pietro Santorelli Chien-Thang Tran

Measurements of the branching fractions of the semileptonic decays B → D ( * ) τ ν ¯ τ and B c → J / ψ τ ν ¯ τ systematically exceed the Standard Model predictions, pointing to possible signals of new physics that can violate lepton flavor universality. The unknown origin of new physics realized in these channels can be probed using a general effective Hamiltonian constructed from four-fermion operators and the corresponding Wilson coefficients. Previously, constraints on these Wilson coefficients were obtained mainly from the experimental data for the branching fractions. Meanwhile, polarization observables were only theoretically studied. The situation has changed with more experimental data having become available, particularly those regarding the polarization of the tau and the D * meson. In this study, we discuss the implications of the new data on the overall picture. We then include them in an updated fit of the Wilson coefficients using all hadronic form factors from our covariant constituent quark model. The use of our form factors provides an analysis independent of those in the literature. Several new-physics scenarios are studied with the corresponding theoretical predictions provided, which are useful for future experimental studies. In particular, we find that under the one-dominant-operator assumption, no operator survives at 1 σ . Moreover, the scalar operators O S L and O S R are ruled out at 2 σ if one uses the constraint B ( B c → τ ν τ ) ≤ 10 % , while the more relaxed constraint B ( B c → τ ν τ ) ≤ 30 % still allows these operators at 2 σ , but only minimally. The inclusion of the new data for the D * polarization fraction F L D * reduces the likelihood of the right-handed vector operator O V R and significantly constrains the tensor operator O T L . Specifically, the F L D * alone rules out O T L at 1 σ . Finally, we show that the longitudinal polarization P L τ of the tau in the decays B → D * τ ν ¯ τ and B c → J / ψ τ ν ¯ τ is extremely sensitive to the tensor operator. Within the 2 σ allowed region, the best-fit value T L = 0.04 + i 0.17 predicts P L τ ( D * ) = − 0.33 and P L τ ( J / ψ ) = − 0.34 , which are at about 33% larger than the Standard Model (SM) prediction P L τ ( D * ) = − 0.50 and P L τ ( J / ψ ) = − 0.51 .

]]>Particles doi: 10.3390/particles3010015

Authors: O. Soloveva P. Moreau L. Oliva V. Voronyuk V. Kireyeu T. Song E. Bratkovskaya

We study the influence of the baryon chemical potential &mu; B on the properties of the Quark&ndash;Gluon&ndash;Plasma (QGP) in and out-of equilibrium. The description of the QGP in equilibrium is based on the effective propagators and couplings from the Dynamical QuasiParticle Model (DQPM) that is matched to reproduce the equation-of-state of the partonic system above the deconfinement temperature T c from lattice Quantum Chromodynamics (QCD). We study the transport coefficients such as the ratio of shear viscosity &eta; and bulk viscosity &zeta; over entropy density s, i.e., &eta; / s and &zeta; / s in the ( T , &mu; ) plane and compare to other model results available at &mu; B = 0 . The out-of equilibrium study of the QGP is performed within the Parton&ndash;Hadron&ndash;String Dynamics (PHSD) transport approach extended in the partonic sector by explicitly calculating the total and differential partonic scattering cross sections based on the DQPM and the evaluated at actual temperature T and baryon chemical potential &mu; B in each individual space-time cell where partonic scattering takes place. The traces of their &mu; B dependences are investigated in different observables for symmetric Au + Au and asymmetric Cu + Au collisions such as rapidity and m T -distributions and directed and elliptic flow coefficients v 1 , v 2 in the energy range 7.7 GeV &le; s N N &le; 200 GeV.

]]>Particles doi: 10.3390/particles3010014

Authors: David Blaschke Alexandra Friesen Yuri Kalinovsky Andrey Radzhabov

The kaon to pion ratios are discussed in the framework of a 2 + 1 flavor PNJL model. In order to interpret the behavior of bound states in medium, the Beth&ndash;Uhlenbeck approach is used. It is shown that, in terms of phase shifts in the K + channel, an additional low-energy mode could appear as a bound state in medium, since the masses of the quark constituents are different. The comparison with experimental data for the ratios is performed and the influence of the anomalous mode to the &ldquo;horn&rdquo; effect in the K + / &pi; + ratio is discussed.

]]>Particles doi: 10.3390/particles3010013

Authors: Mădălina Mihaela Miloi [DsTau Collaboration] [DsTau Collaboration]

For clarifying the validity of the Lepton Universality hypothesis, one of the fundamental statements of the Standard Model, the interaction cross section for all three flavors of leptons have to be known with high precision. In neutrino sector, for electron and muon neutrinos, the interaction cross section is known fairly well, but for tau neutrino only poor estimations exist. In particular, the most direct measurement by the DONuT experiment was performed with rather poor accuracy due to low statistics and an uncertainty of the tau neutrino flux. The DsTau experiment proposes to study tau-neutrino production process and thus to improve significantly the accuracy of calculations of tau neutrino flux for neutrino accelerator experiments. To study reactions providing most of tau neutrinos, the experiment uses a setup based on high resolution nuclear emulsions, capable to register short lived particle decays created in proton-nucleus interactions. The present report is an overview of the DsTau experiment together with some of the preliminary results from the pilot run.

]]>Particles doi: 10.3390/particles3010012

Authors: Pietro Colangelo Fulvia De Fazio Francesco Loparco

Anomalies recently observed in semileptonic b &rarr; c ℓ &minus; &nu; &macr; ℓ and b &rarr; s ℓ + ℓ &minus; transitions point to violation of Lepton Flavour Universality. Strategies for new analyses of different modes are required, in particular for the modes induced by the b &rarr; u transition. We describe the purely leptonic B decay, the B &macr; &rarr; &pi; ℓ &minus; &nu; &macr; ℓ channel and the B semileptonic modes to &rho; ( 770 ) and a 1 ( 1260 ) in extensions of the Standard Model involving Lepton Flavour Universality violating b &rarr; u operators. In particular, we review the observables in the four-dimensional angular B &macr; &rarr; &rho; ( &pi; &pi; ) ℓ &minus; &nu; &macr; ℓ and B &macr; &rarr; a 1 ( &rho; &pi; ) ℓ &minus; &nu; &macr; ℓ distributions, suitable to pin down deviations from the Standard Model. We discuss the complementarity among the various modes for New Physics searches.

]]>Particles doi: 10.3390/particles3010011

Authors: Mikhail A. Ivanov

In this lecture, we provide a basic introduction into the topic of charmed baryons and their nonleptonic two-body decays. Some features of the baryon weak decays on the quark level are discussed in detail in the framework of effective field theory. The calculation of the matrix elements of the four-quark operators arising in the effective theory proceeds by using the covariant constituent quark model. The model allows one to evaluate not only the factorizing tree-level diagrams but also more complicated diagrams with the internal W&ndash;exchange. The technique required for such calculation is discussed in some detail. Finally, the numerical results are presented, and comparison of the contributions coming from the W&ndash;exchange diagrams with those from the tree-level are carefully performed.

]]>Particles doi: 10.3390/particles3010010

Authors: Yuri Sinyukov Musfer Adzhymambetov Volodymyr Shapoval

The paper is devoted to the theoretical study of particle production in the Large Hadron Collider (LHC) Xe+Xe collisions at the energy s N N = 5 . 44 TeV. The description of common bulk observables, such as mean charged particle multiplicity, particle number ratios, and p T spectra, is obtained within the integrated hydrokinetic model, and the simulation results are compared to the corresponding experimental points. The comparison shows that the model is able to adequately describe the measured data for the considered collision type, similarly as for the cases of Pb+Pb LHC collisions and top Relativistic Heavy Ion Collider (RHIC) energy Au+Au collisions, analyzed in our previous works.

]]>Particles doi: 10.3390/particles3010009

Authors: Dmitri Melikhov

We discuss dispersion representations for the triangle diagram F ( q 2 , p 1 2 , p 2 2 ) , the single dispersion representation in q 2 and the double dispersion representation in p 1 2 and p 2 2 , with special emphasis on the appearance of the anomalous singularities and the anomalous cuts in these representations.

]]>Particles doi: 10.3390/particles3010008

Authors: Christof Gattringer Michael Mandl Pascal Törek

We discuss two new density of states approaches for finite density lattice QCD (Quantum Chromo Dynamics). The paper extends a recent presentation of the new techniques based on Wilson fermions, while here, we now discuss and test the case of finite density QCD with staggered fermions. The first of our two approaches is based on the canonical formulation where observables at a fixed net quark number N are obtained as Fourier moments of the vacuum expectation values at imaginary chemical potential &theta; . We treat the latter as densities that can be computed with the recently developed functional fit approach. The second method is based on a direct grand canonical evaluation after rewriting the QCD partition sum in terms of a suitable pseudo-fermion representation. In this form, the imaginary part of the pseudo-fermion action can be identified and the corresponding density may again be computed with the functional fit approach. We develop the details of the two approaches and discuss some exploratory first tests for the case of free fermions where reference results for assessing the new techniques may be obtained from Fourier transformation.

]]>Particles doi: 10.3390/particles3010007

Authors: Bastian B. Brandt Francesca Cuteri Gergely Endrődi Sebastian Schmalzbauer

For large isospin asymmetries, perturbation theory predicts the quantum chromodynamic (QCD) ground state to be a superfluid phase of u and d &macr; Cooper pairs. This phase, which is denoted as the Bardeen-Cooper-Schrieffer (BCS) phase, is expected to be smoothly connected to the standard phase with Bose-Einstein condensation (BEC) of charged pions at &mu; I &ge; m &pi; / 2 by an analytic crossover. A first hint for the existence of the BCS phase, which is likely characterised by the presence of both deconfinement and charged pion condensation, comes from the lattice observation that the deconfinement crossover smoothly penetrates into the BEC phase. To further scrutinize the existence of the BCS phase, in this article we investigate the complex spectrum of the massive Dirac operator in 2+1-flavor QCD at nonzero temperature and isospin chemical potential. The spectral density near the origin is related to the BCS gap via a generalization of the Banks-Casher relation to the case of complex Dirac eigenvalues (derived for the zero-temperature, high-density limits of QCD at nonzero isospin chemical potential).

]]>Particles doi: 10.3390/particles3010006

Authors: Tamaz G. Khunjua Konstantin G. Klimenko Roman N. Zhokhov

Recently it has been found that quantum chromodynamics (QCD) phase diagram possesses a duality between chiral symmetry breaking and pion condensation. For the first time this was revealed in the QCD motivated toy model. Then it was demonstrated in effective models as well and new additional dualities being found. We briefly recap the main features of this story and then discuss its applications as a tool to explore the QCD phase structure. The most appealing application is the possibility of getting the results on the QCD phase diagram at large baryon density. Taking the idea from large 1 / N c universalities it was argued that the scenario of circumventing the sign problem with the help of dualities seems plausible. It is also discussed that there is a persistent problem about whether there should be catalysis or anti-catalysis of chiral symmetry breaking by chiral imbalance. One can probably say that the issue is settled after lattice results (first principle approach), where the catalysis was observed. But they used an unphysically large pion mass so it is still interesting to get additional indications that this is the case. It is shown just by the duality property that there exists catalysis of chiral symmetry breaking. So, having in mind our results and the earlier lattice simulations, one can probably claim that this issue is settled. It is demonstrated that the duality can be used to obtain new results. As an example, it is showcased how the phase structure of dense quark matter with chiral imbalance (with possibility of inhomogeneous phases) can be obtained from the knowledge of a QCD phase diagram with isopin asymmetry.

]]>Particles doi: 10.3390/particles3010005

Authors: Felix Karbstein

These notes provide a pedagogical introduction to the theoretical study of vacuum polarization effects in strong electromagnetic fields as provided by state-of-the-art high-intensity lasers. Quantum vacuum fluctuations give rise to effective couplings between electromagnetic fields, thereby supplementing Maxwell&rsquo;s linear theory of classical electrodynamics with nonlinearities. Resorting to a simplified laser pulse model, allowing for explicit analytical insights, we demonstrate how to efficiently analyze all-optical signatures of these effective interactions in high-intensity laser experiments. Moreover, we highlight several key features relevant for the accurate planning and quantitative theoretical analysis of quantum vacuum nonlinearities in the collision of high-intensity laser pulses.

]]>Particles doi: 10.3390/particles3010004

Authors: Alexei Larionov Mark Strikman

An incoming or outgoing hadron in a hard collision with large momentum transfer gets squeezed in the transverse direction to its momentum. In the case of nuclear targets, this leads to the reduced interaction of such hadrons with surrounding nucleons which is known as color transparency (CT). The identification of CT in exclusive processes on nuclear targets is of significant interest not only by itself but also due to the fact that CT is a necessary condition for the applicability of factorization for the description of the corresponding elementary process. In this paper we discuss the semiexclusive processes A ( e , e &prime; &pi; + ) , A ( &pi; &minus; , l &minus; l + ) and A ( &gamma; , &pi; &minus; p ) . Since CT is closely related to hadron formation mechanism, the reduced interaction of &rsquo;pre-hadrons&rsquo; with nucleons is a common feature of generic high-energy inclusive processes on nuclear targets, such as hadron attenuation in deep inelastic scattering (DIS). We will discuss the novel way to study hadron formation via slow neutron production induced by a hard photon interaction with a nucleus. Finally, the opportunity to study hadron formation effects in heavy-ion collisions in the NICA regime will be considered.

]]>Particles doi: 10.3390/particles3010003

Authors: Particles Editorial Office Particles Editorial Office

The editorial team greatly appreciates the reviewers who have dedicated their considerable time and expertise to the journal&rsquo;s rigorous editorial process over the past 12 months, regardless of whether the papers are finally published or not [...]

]]>Particles doi: 10.3390/particles3010002

Authors: Alexander Andrianov Vladimir Andrianov Domenec Espriu

We compare the chiral perturbation theory (ChPT) and the linear sigma model (LSM) as realizations of low energy quantum chromodynamics (QCD) for light mesons in a chirally-imbalanced medium. The relations between the low-energy constants of the chiral Lagrangian and the corresponding constants of the linear sigma model are established as well as the expressions for the decay constant of &pi; -meson in the medium and for the mass of the a 0 . In the large N c count taken from QCD the correspondence of ChPT and LSM is remarkably good and provides a solid ground for the search of chiral imbalance manifestations in pion physics. A possible experimental detection of chiral imbalance (and therefore a phase with local parity breaking) is outlined in the charged pion decays inside the fireball.

]]>Particles doi: 10.3390/particles3010001

Authors: Georgy Prokhorov Oleg Teryaev Valentin Zakharov

The relativistic form of the Zubarev density operator can be used to study quantum effects associated with acceleration of the medium. In particular, it was recently shown that the calculation of perturbative corrections in acceleration based on the Zubarev density operator makes it possible to show the existence of the Unruh effect. In this paper, we present the details of the calculation of quantum correlators arising in the fourth order of the perturbation theory needed to demonstrate the Unruh effect. Expressions for the quantum corrections for massive fermions are also obtained.

]]>Particles doi: 10.3390/particles2040032

Authors: Benjamin Rabe Burkhard Kämpfer

We argue for a continuous (dynamical) kinetic freeze-out of K &plusmn; , ϕ observed at midrapidity in collisions of Au(1.23 A GeV) + Au. The simulations, by means of a transport model of Boltzmann-&Uuml;hling-Uhlenbeck (BUU) type, point to time independent transverse momentum slope parameters after 20 fm/c. The complex interplay of expansion dynamics and strangeness production/exchange/absorption as well as elastic scatterings involved in the reaction network does not support the previous interpretation of a late freeze-out of K &minus; due to larger cross sections.

]]>Particles doi: 10.3390/particles2040031

Authors: Peter Senger

The Compressed Baryonic Matter (CBM) experiment is one of four scientific pillars of the future Facility for Antiproton and Ion Research (FAIR) in Darmstadt. In collisions between heavy nuclei at FAIR energies, it is expected that the matter in the reaction zone is compressed to more than five times saturation density, corresponding to the density in the core of a massive neutron star. This offers the unique opportunity to study in the laboratory the high-density equation-of-state (EOS) of nuclear matter, and to search for new phases of Quantum Chromo Dynamics (QCD) matter at large baryon-chemical potentials. Promising experimental observables sensitive to the EOS and to possible phase transitions will be discussed, together with a brief description of the CBM experiment.

]]>Particles doi: 10.3390/particles2040030

Authors: Rudolf Golubich Manfried Faber

The center vortex model of quantum chromodynamic states that vortices, a closed color-magnetic flux, percolate the vacuum. Vortices are seen as the relevant excitations of the vacuum, causing confinement and dynamical chiral symmetry breaking. In an appropriate gauge, as direct maximal center gauge, vortices are detected by projecting onto the center degrees of freedom. Such gauges suffer from Gribov copy problems: different local maxima of the corresponding gauge functional can result in different predictions of the string tension. By using nontrivial center regions&mdash;that is, regions whose boundary evaluates to a nontrivial center element&mdash;a resolution of this issue seems possible. We use such nontrivial center regions to guide simulated annealing procedures, preventing an underestimation of the string tension in order to resolve the Gribov copy problem.

]]>Particles doi: 10.3390/particles2040029

Authors: Peter Senger Dmitrii Dementev Johann Heuser Mikhail Kapishin Evgeny Lavrik Yuri Murin Anna Maksymchuk Hans Rudolf Schmidt Christian Schmidt Anna Senger Alexander Zinchenko

The Nuclotron at the Joint Institute for Nuclear Research in Dubna can deliver gold beams with kinetic energies between 2 and 4.5 A GeV. In heavy-ion collisions at these energies, it is expected that the nuclear fireball will be compressed by up to approximately four times the saturation density. This offers the opportunity to study the high-density equation-of-state (EOS) of nuclear matter in the laboratory, which is needed for our understanding of the structure of neutron stars and the dynamics of neutron star mergers. The Baryonic Matter at the Nuclotron (BM@N) experiment will be upgraded to perform multi-differential measurements of hadrons including (multi-) strange hyperons, which are promising probes of the high-density EOS, and of new phases of quantum chromodynamic (QCD) matter. The layout of the upgraded BM@N experiment and the results of feasibility studies are presented.

]]>Particles doi: 10.3390/particles2040028

Authors: Nils Andersson Andreas Schmitt

Two coupled, interpenetrating fluids suffer instabilities beyond certain critical counterflows. For ideal fluids, an energetic instability occurs at the point where a sound mode inverts its direction due to the counterflow, while dynamical instabilities only occur at larger relative velocities. Here, we discuss two relativistic fluids, one of which is dissipative. Using linearized hydrodynamics, we show that, in this case, the energetic instability turns dynamical, i.e., there is an exponentially growing mode, and this exponential growth only occurs in the presence of dissipation. This result is general and does not rely on an underlying microscopic theory. It can be applied to various two-fluid systems, for instance, in the interior of neutron stars. We also point out that, under certain circumstances, the two-fluid system exhibits a mode analogous to the r-mode in neutron stars that can become unstable for arbitrarily small values of the counterflow.

]]>Particles doi: 10.3390/particles2040027

Authors: Marc Salinas Thomas Klähn Prashanth Jaikumar

The vector interaction enhanced Bag model (vBag) for dense quark matter extends the commonly used thermodynamic Bag model (tdBag) by incorporating effects of dynamical chiral symmetry breaking (D &chi; SB) and vector repulsion. Motivated by the suggestion that the stability of strange matter is in tension with chiral symmetry breaking (D &chi; SB) we examine the parameter space for its stability in the vBag model in this work. Assuming the chiral transition occurs at sufficiently low density, we determine the stability region of strange matter as a function of the effective Bag constant and the vector coupling. As an astrophysical application, we construct contours of maximum mass M max and radius at maximum mass R max in this region of parameter space. We also study the stability of strange stars in the vBag model with maximum mass in the 2 M ⊙ range by computing the spectrum of radial oscillations, and comparing to results from the tdBag model, find some notable differences.

]]>Particles doi: 10.3390/particles2040026

Authors: Armen Sedrakian

This Special Issue arose from the presentations of the authors at the international conference &ldquo;The Modern Physics of Compact Stars and Relativistic Gravity 2017&rdquo; https://indico [...]

]]>Particles doi: 10.3390/particles2030025

Authors: Massimo Mannarelli

We give a pedagogical review of the properties of the various meson condensation phases triggered by a large isospin or strangeness imbalance. We argue that these phases are extremely interesting and powerful playground for exploring the properties of hadronic matter. The reason is that they are realized in a regime in which various theoretical methods overlap with increasingly precise numerical lattice QCD simulations, providing insight on the properties of color confinement and of chiral symmetry breaking.

]]>Particles doi: 10.3390/particles2030024

Authors: Matthew Bernard Vladislav A. Guskov Mikhail G. Ivanov Alexey E. Kalugin Stanislav L. Ogarkov

Nonlocal quantum field theory (QFT) of one-component scalar field &phi; in D-dimensional Euclidean spacetime is considered. The generating functional (GF) of complete Green functions Z as a functional of external source j, coupling constant g and spatial measure d &mu; is studied. An expression for GF Z in terms of the abstract integral over the primary field &phi; is given. An expression for GF Z in terms of integrals over the primary field and separable Hilbert space (HS) is obtained by means of a separable expansion of the free theory inverse propagator L ^ over the separable HS basis. The classification of functional integration measures D &phi; is formulated, according to which trivial and two nontrivial versions of GF Z are obtained. Nontrivial versions of GF Z are expressed in terms of 1-norm and 0-norm, respectively. In the 1-norm case in terms of the original symbol for the product integral, the definition for the functional integration measure D &phi; over the primary field is suggested. In the 0-norm case, the definition and the meaning of 0-norm are given in terms of the replica-functional Taylor series. The definition of the 0-norm generator &Psi; is suggested. Simple cases of sharp and smooth generators are considered. An alternative derivation of GF Z in terms of 0-norm is also given. All these definitions allow to calculate corresponding functional integrals over &phi; in quadratures. Expressions for GF Z in terms of integrals over the separable HS, aka the basis functions representation, with new integrands are obtained. For polynomial theories &phi; 2 n , n = 2 , 3 , 4 , &hellip; , and for the nonpolynomial theory sinh 4 &phi; , integrals over the separable HS in terms of a power series over the inverse coupling constant 1 / g for both norms (1-norm and 0-norm) are calculated. Thus, the strong coupling expansion in all theories considered is given. &ldquo;Phase transitions&rdquo; and critical values of model parameters are found numerically. A generalization of the theory to the case of the uncountable integral over HS is formulated&mdash;GF Z for an arbitrary QFT and the strong coupling expansion for the theory &phi; 4 are derived. Finally a comparison of two GFs Z , one on the continuous lattice of functions and one obtained using the Parseval&ndash;Plancherel identity, is given.

]]>Particles doi: 10.3390/particles2030023

Authors: Henrique Gieg Tim Dietrich Maximiliano Ujevic

The gravitational wave and electromagnetic signatures connected to the merger of two neutron stars allow us to test the nature of matter at supranuclear densities. Since the Equation of State governing the interior of neutron stars is only loosely constrained, there is even the possibility that strange quark matter exists inside the core of neutron stars. We investigate how strange quark matter cores affect the binary neutron star coalescence by performing numerical relativity simulations. Interestingly, the strong phase transition can cause a reduction of the convergence order of the numerical schemes to first order if the numerical resolution is not high enough. Therefore, an additional challenge is added in producing high-quality gravitational wave templates for Equation of States with a strong phase transition. Focusing on one particular configuration of an equal mass configuration consistent with GW170817, we compute and discuss the associated gravitational wave signal and some of the electromagnetic counterparts connected to the merger of the two stars. We find that existing waveform approximants employed for the analysis of GW170817 allow describing this kind of systems within the numerical uncertainties, which, however, are several times larger than for pure hadronic Equation of States, which means that even higher resolutions have been employed for an accurate gravitational wave model comparison. We also show that for the chosen Equation of State, quasi-universal relations describing the gravitational wave emission after the moment of merger seem to hold and that the electromagnetic signatures connected to our chosen setup would not be bright enough to explain the kilonova associated to GW170817.

]]>Particles doi: 10.3390/particles2030022

Authors: Igor V. Anikin

Using the light-cone sum rules at leading order, we present an approach to perform the preliminary upper estimation for the nucleon gravitational form factor D ( t ) (D-term contribution). Comparison with the experimental data and with the results of different models is discussed.

]]>Particles doi: 10.3390/particles2020021

Authors: Thomas Gutsche Mikhail Ivanov Jürgen Körner Valery Lyubovitskij

The recent discovery of double charm baryon states by the LHCb Collaborarion and their high precision mass determination calls for a comprehensive analysis of the nonleptonic decays of double and single heavy baryons. Nonleptonic baryon decays play an important role in particle phenomenology since they allow for studying the interplay of long and short distance dynamics of the Standard Model (SM). Furthermore, they allow one to search for New Physics effects beyond the SM. We review recent progress in experimental and theoretical studies of the nonleptonic decays of heavy baryons with a focus on double charm baryon states and their decays. In particular, we discuss new ideas proposed by the present authors to calculate the W-exchange matrix elements of the nonleptonic decays of double heavy baryons. An important ingredient in our approach is the compositeness condition of Salam and Weinberg, and an effective implementation of infrared confinement both of which allow one to describe the nonperturbative structure of baryons composed of light and heavy quarks. Furthermore, we discuss an ab initio calculational method for the treatment of the so-called W-exchange diagrams generated by W ± boson exchange between quarks. We found that the W ± -exchange contributions are not suppressed in comparison with the tree-level (factorizing) diagrams and must be taken into account in the evaluation of matrix elements. Moreover, there are decay processes such as the doubly Cabibbo-suppressed decay Ξ c + → p ϕ recently observed by the LHCb Collaboration, which is contributed to only by one single W-exchange diagram.

]]>Particles doi: 10.3390/particles2020020

Authors: Gerd Röpke

The method of Zubarev allows one to construct a statistical operator for the nonequilibrium. The von Neumann equation is modified introducing a source term that is considered as an infinitesimal small correction. This approach provides us with a very general and unified treatment of nonequilibrium processes. Considering as an example the electrical conductivity, we discuss the modification of the von Neumann equation to describe a stationary nonequilibrium process. The Zubarev approach has to be generalized to open quantum systems. The interaction of the system with the irrelevant degrees of freedom of the bath is globally described by the von Neumann equation with a finite source term. This is interpreted as a relaxation process to an appropriate relevant statistical operator. As an alternative, a quantum master equation can be worked out where the coupling to the bath is described by a dissipator. The production of entropy is analyzed.

]]>Particles doi: 10.3390/particles2020019

Authors: Ashot Gevorkyan

We consider the formation of structured and massless particles with spin 1, by using the Yang&ndash;Mills-like stochastic equations system for the group symmetry S U ( 2 ) &otimes; U ( 1 ) without taking into account the nonlinear term characterizing self-action. We prove that, in the first phase of relaxation, as a result of multi-scale random fluctuations of quantum fields, massless particles with spin 1, further referred as hions, are generated in the form of statistically stable quantized structures, which are localized on 2D topological manifolds. We also study the wave state and the geometrical structure of the hion when as a free particle and, accordingly, while it interacts with a random environment becoming a quasi-particle with a finite lifetime. In the second phase of relaxation, the vector boson makes spontaneous transitions to other massless and mass states. The problem of entanglement of two hions with opposite projections of the spins + 1 and &minus; 1 and the formation of a scalar zero-spin boson are also thoroughly studied. We analyze the properties of the scalar field and show that it corresponds to the Bose&ndash;Einstein (BE) condensate. The scalar boson decay problems, as well as a number of features characterizing the stability of BE condensate, are also discussed. Then, we report on the structure of empty space&ndash;time in the context of new properties of the quantum vacuum, implying on the existence of a natural quantum computer with complicated logic, which manifests in the form of dark energy. The possibilities of space&ndash;time engineering are also discussed.

]]>Particles doi: 10.3390/particles2020018

Authors: Masaru Hongo Yoshimasa Hidaka

A derivation of anomaly-induced transport phenomena&mdash;the chiral magnetic/vortical effect&mdash;is revisited based on the imaginary-time formalism of quantum field theory. Considering the simplest anomalous system composed of a single Weyl fermion, we provide two derivations: perturbative (one-loop) evaluation of the anomalous transport coefficient, and the anomaly matching for the local thermodynamic functional.

]]>Particles doi: 10.3390/particles2020017

Authors: Mikhail Veysman Gerd Röpke Heidi Reinholz

The fruitfulness of the method of a non-equilibrium statistical operator (NSO) and generalized linear response theory is demonstrated calculating the permittivity, dynamical conductivity, absorption coefficient, and dynamical collision frequency of plasmas in the degenerate, metallic state as well as classical plasmas. A wide range of plasma parameters is considered, and a wide range of frequencies of laser radiation acting on such plasmas is treated. New analytical expressions for the plasma response are obtained by this method, and several limiting cases are discussed.

]]>Particles doi: 10.3390/particles2020016

Authors: Brent Harrison Andre Peshier

We present a novel numerical scheme to solve the QCD Boltzmann equation in the soft scattering approximation, for the quenched limit of QCD. Using this we can readily investigate the evolution of spatially homogeneous systems of gluons distributed isotropically in momentum space. We numerically confirm that for so-called &ldquo;overpopulated&rdquo; initial conditions, a (transient) Bose-Einstein condensate could emerge in a finite time. Going beyond existing results, we analyze the formation dynamics of this condensate. The scheme is extended to systems with cylindrically symmetric momentum distributions, in order to investigate the effects of anisotropy. In particular, we compare the rates at which isotropization and equilibration occur. We also compare our results from the soft scattering scheme to the relaxation time approximation.

]]>Particles doi: 10.3390/particles2020015

Authors: Stanislav A. Smolyansky Anatolii D. Panferov David B. Blaschke Narine T. Gevorgyan

On the basis of the well-known kinetic description of e &minus; e + vacuum pair creation in strong electromagnetic fields in D = 3 + 1 QED we construct a nonperturbative kinetic approach to electron-hole excitations in graphene under the action of strong, time-dependent electric fields. We start from the simplest model of low-energy excitations around the Dirac points in the Brillouin zone. The corresponding kinetic equations are analyzed by nonperturbative analytical and numerical methods that allow to avoid difficulties characteristic for the perturbation theory. We consider different models for external fields acting in both, one and two dimensions. In the latter case we discuss the nonlinear interaction of the orthogonal currents in graphene which plays the role of an active nonlinear medium. In particular, this allows to govern the current in one direction by means of the electric field acting in the orthogonal direction. Investigating the polarization current we detected the existence of high frequency damped oscillations in a constant external electric field. When the electric field is abruptly turned off residual inertial oscillations of the polarization current are obtained. Further nonlinear effects are discussed.

]]>Particles doi: 10.3390/particles2020014

Authors: Francesco Becattini Matteo Buzzegoli Eduardo Grossi

In this work, the nonequilibrium density operator approach introduced by Zubarev more than 50 years ago to describe quantum systems at a local thermodynamic equilibrium is revisited. This method, which was used to obtain the first &ldquo;Kubo&rdquo; formula of shear viscosity, is especially suitable to describe quantum effects in fluids. This feature makes it a viable tool to describe the physics of Quark&ndash;Gluon Plasma in relativistic nuclear collisions.

]]>Particles doi: 10.3390/particles2020013

Authors: Gurjav Ganbold

The phenomena of strong running coupling and hadron mass generating have been studied in the framework of a QCD-inspired relativistic model of quark-gluon interaction with infrared-confined propagators. We derived a meson mass equation and revealed a specific new behavior of the mass-dependent strong coupling &alpha; ^ s ( M ) defined in the time-like region. A new infrared freezing point &alpha; ^ s ( 0 ) = 1.03198 at origin has been found and it did not depend on the confinement scale &Lambda; &gt; 0 . Independent and new estimates on the scalar glueball mass, &lsquo;radius&rsquo; and gluon condensate value have been performed. The spectrum of conventional mesons have been calculated by introducing a minimal set of parameters: the masses of constituent quarks and &Lambda; . The obtained values are in good agreement with the latest experimental data with relative errors less than 1.8 percent. Accurate estimates of the leptonic decay constants of pseudoscalar and vector mesons have been performed.

]]>Particles doi: 10.3390/particles2020012

Authors: David B. Blaschke Lukasz Juchnowski Andreas Otto

The kinetic-equation approach to particle production in strong, time-dependent external fields is revisited and three limiting cases are discussed for different field patterns: the Sauter pulse, a harmonic pulse with a Gaussian envelope, and a Poisson-distributed stochastic field. It is shown that for transient subcritical electric fields E ( t ) a finite residual particle number density n ( &infin; ) would be absent if the field-dependence of the dynamical phase in the Schwinger source term would be neglected. In this case the distribution function of created particles follows the law f ( t ) &sim; E 2 ( t ) . Two lessons for particle production in heavy-ion collisions are derived from this exercise. First: the shorter the (Sauter-type) pulse, the higher the residual density of produced particles. Second: although the Schwinger process in a string-type field produces a non-thermal particle spectrum, a Poissonian distribution of the (fluctuating) strings produces a thermal spectrum with an apparent temperature that coincides with the Hawking&ndash;Unruh temperature for the mean value of the string tension.

]]>Particles doi: 10.3390/particles2010011

Authors: Yuri G. Rudoy Yuri P. Rybakov

The problem of pressure fluctuations in the thermal equilibrium state of some objects is discussed, its solution being suggested via generalizing the Bogoliubov&ndash;Zubarev theorem. This theorem relates the thermodynamic pressure with the Hamilton function and its derivatives describing the object in question. It is shown that unlike to other thermodynamic quantities (e.g., the energy or the volume) the pressure fluctuations are described not only by a purely thermodynamic quantity (namely, the corresponding thermodynamic susceptibility) but also by some non-thermodynamic quantities. The attempt is made to apply these results to the relativistic ideal gases, with some numerical results being valid for the limiting ultra-relativistic or high-temperature case.

]]>Particles doi: 10.3390/particles2010010

Authors: Elizaveta Nazarova Łukasz Juchnowski David Blaschke Tobias Fischer

We study the particle production in the early stage of the ultrarelativistic heavy-ion collisions. To this end the Boltzmann kinetic equations for gluons and pions with elastic rescattering are considered together with a simple model for the parton-hadron conversion process (hadronisation). It is shown that the overpopulation of the gluon phase space in the initial state leads to an intermediate stage of Bose enhancement in the low-momentum gluon sector which due to the gluon-pion conversion process is then reflected in the final distribution function of pions. This pattern is very similar to the experimental finding of a low-momentum pion enhancement in the ALICE experiment at the CERN Large Hadron Collider (LHC). Relations to the thermal statistical model of hadron production and the phenomenon of thermal and chemical freeze-out are discussed in this context.

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