Particles doi: 10.3390/particles7020028

Authors: Pooja Bhattacharjee Francesca Calore

This study explores the potential for dark matter annihilation within brown dwarfs, investigating an unconventional mechanism for neutrino production. Motivated by the efficient accumulation of dark matter particles in brown dwarfs through scattering interactions, we focus on a mass range above 10 GeV, considering dark matter annihilation channels &chi;&chi;&rarr;&nu;&nu;&macr;&nu;&nu;&macr; through long-lived mediators. Using the projected sensitivity of IceCube Generation 2, we assess the detection capability of the local population of brown dwarfs within 20 pc and exclude dark matter-nucleon scattering with cross-sections as low as a few multiples of 10&minus;36cm2.

]]>Particles doi: 10.3390/particles7020027

Authors: Francesco Dimiccoli Francesco Maria Follega

Analyzing the isotopic composition of cosmic rays (CRs) provides valuable insights into the galactic environment and helps refine existing propagation models. A particular interest is devoted to secondary-to-primary ratios of light isotopic components of CRs, the measurement of which can provide complementary information with respect to secondary-to-primary ratios like B/C. Given the complexity of the concurrent measurement of velocity and momentum required to differentiate isotopes of the same Z, a task typically accomplished using magnetic spectrometers, existing measurements of these ratios only effectively characterize the low-energy region (below 1 GeV/nucl). This study introduces a novel technique for isotopic distinction in CRs at high energies up to 100 GeV/nucl based on multiple scattering, which, combined with the proposed measurement of velocity, represent an interesting alternative to magnetic spectrometers. The performance of this technique was assessed through a dedicated simulation using the GEANT4 package, with specific emphasis on Z = 1 isotopes.

]]>Particles doi: 10.3390/particles7020026

Authors: Ken-ji Hamada

The effective action in the renormalizable quantum theory of gravity provides entropy because the total Hamiltonian vanishes. Since it is a renormalization group invariant that is constant in the process of cosmic evolution, we can show conservation of entropy, which is an ansatz in the standard cosmology. Here, we study renormalizable quantum gravity that exhibits conformal dominance at high energy beyond the Planck scale. The current entropy of the universe is derived by calculating the effective action under the scenario of quantum gravity inflation caused by its dynamics. We then argue that ghost modes must be unphysical but are necessary for the Hamiltonian to vanish and for entropy to exist in gravitational systems.

]]>Particles doi: 10.3390/particles7020025

Authors: Davide Fiscaletti Ignazio Licata

A model of a physical vacuum defined by a Gross&ndash;Pitaevskij equation and characterized by dissipative features close to the Planck scale is proposed, which provides an emergent explanation of scales, hierarchies and Higgs mass generation of the Standard Model. A fundamental nonlocal and nonlinear texture of the vacuum is introduced in terms of planckeons, sub-Planckian objects defined by a generalized Compton wavelength, which lead to find Planckian signatures of the Standard Model.

]]>Particles doi: 10.3390/particles7020024

Authors: Marta Borchiellini Leandro Mano Fernando Barão Manuela Vecchi

Isotopic composition measurements of singly charged cosmic rays (CR) provide essential insights into CR transport in the Galaxy. The Alpha Magnetic Spectrometer (AMS-02) can identify singly charged isotopes up to about 10 GeV/n. However, their identification presents challenges due to the small abundance of CR deuterons compared to the proton background. In particular, a high accuracy for the velocity measured by a ring-imaging Cherenkov detector (RICH) is needed to achieve a good isotopic mass separation over a wide range of energies. The velocity measurement with the RICH is particularly challenging for Z=1 isotopes due to the low number of photons produced in the Cherenkov rings. This faint signal is easily disrupted by noisy hits leading to a misreconstruction of the particles&rsquo; ring. Hence, an efficient background reduction process is needed to ensure the quality of the reconstructed Cherenkov rings and provide a correct measurement of the particles&rsquo; velocity. Machine learning methods, particularly boosted decision trees, are well suited for this task, but their performance relies on the choice of the features needed for their training phase. While physics-driven feature selection methods based on the knowledge of the detector are often used, machine learning algorithms for automated feature selection can provide a helpful alternative that optimises the classification method&rsquo;s performance. We compare five algorithms for selecting the feature samples for RICH background reduction, achieving the best results with the Random Forest method. We also test its performance against the physics-driven selection method, obtaining better results.

]]>Particles doi: 10.3390/particles7020023

Authors: Maksym Teslyk Larissa Bravina Evgeny Zabrodin

Olena Teslyk and Lidiia Zadorozhna request the removal of their names from the author list of this publication [...]

]]>Particles doi: 10.3390/particles7020022

Authors: Arpan Chatterjee Marco Frasca Anish Ghoshal Stefan Groote

We derive a Nambu&ndash;Jona-Lasinio (NJL) model from a non-local gauge theory and show that it has confining properties at low energies. In particular, we present an extended approach to non-local QCD and a complete revision of the technique of Bender, Milton and Savage applied to non-local theories, providing a set of Dyson&ndash;Schwinger equations in differential form. In the local case, we obtain closed-form solutions in the simplest case of the scalar field and extend it to the Yang&ndash;Mills field. In general, for non-local theories, we use a perturbative technique and a Fourier series and show how higher-order harmonics are heavily damped due to the presence of the non-local factor. The spectrum of the theory is analysed for the non-local Yang&ndash;Mills sector and found to be in agreement with the local results on the lattice in the limit of the non-locality mass parameter running to infinity. In the non-local case, we confine ourselves to a non-locality mass that is sufficiently large compared to the mass scale arising from the integration of the Dyson&ndash;Schwinger equations. Such a choice results in good agreement, in the proper limit, with the spectrum of the local theory. We derive a gap equation for the fermions in the theory that gives some indication of quark confinement in the non-local NJL case as well. Confinement seems to be a rather ubiquitous effect that removes some degrees of freedom in the original action, favouring the appearance of new observable states, as seen, e.g., for quantum chromodynamics at lower energies.

]]>Particles doi: 10.3390/particles7020021

Authors: Pitchayapak Kitisri Jatuporn Saisut Sakhorn Rimjaem

The establishment of the mid-infrared and terahertz free-electron laser (MIR/THz FEL) facility is ongoing at the PBP-CMU Electron Linac Laboratory (PCELL) in Chiang Mai University. The facility utilizes an S-band radio-frequency (RF) gun and a linear accelerator (linac) to generate and accelerate electron bunches. These electron bunches are accelerated in the RF gun and the linac using RF pulses with a frequency of 2856 MHz. Measuring the RF properties becomes essential, as the RF pulse information can be utilized to estimate the electron beam properties. To achieve the measurement results, we employed an RF measurement system comprising directional couplers, coaxial cables, attenuators, a crystal detector, and an oscilloscope. Prior to conducting measurements, the crystal detector and RF equipment were calibrated and characterized to ensure precise and reliable results. The electron beam energy estimation using the measured RF power was compared with the measured beam energies. The gun and the linac were operated with an absorbed RF power of 1.52 MW and an input power of 1.92 MW, respectively. The estimated electron beam energies were found to be 2.18 MeV and 15.0 MeV, respectively, closely aligning with the measured beam energies of 2.1 MeV and 14.0 MeV after the gun and linac acceleration. These consistent energy values support the reliability of our RF power measurement system and procedure.

]]>Particles doi: 10.3390/particles7020020

Authors: Daniel Melo Edilson Reyes Raffaele Fazio

We review the hadronic light-by-light (HLbL) contribution to the muon anomalous magnetic moment. Upcoming measurements will reduce the experimental uncertainty of this observable by a factor of four; therefore, the theoretical precision must improve accordingly to fully harness such an experimental breakthrough. With regards to the HLbL contribution, this implies a study of the high-energy intermediate states that are neglected in dispersive estimates. We focus on the maximally symmetric high-energy regime and in-quark loop approximation of perturbation theory, following the method of the OPE with background fields proposed by Bijnens et al. in 2019 and 2020. We confirm their results regarding the contributions to the muon g&minus;2. For this, we use an alternative computational method based on a reduction in the full quark loop amplitude, instead of projecting on a supposedly complete system of tensor structures motivated by first principles. Concerning scalar coefficients, mass corrections have been obtained by hypergeometric representations of Mellin&ndash;Barnes integrals. By our technique, the completeness of such kinematic singularity/zero-free tensor decomposition of the HLbL amplitude is explicitly checked.

]]>Particles doi: 10.3390/particles7020019

Authors: Seokcheon Lee

It is known that dimensional constants, such as ℏ, c, G, e, and k, are merely human constructs whose values and units vary depending on the chosen system of measurement. Therefore, the time variations in dimensional constants lack operational significance due to their dependence on these dimensional constants. They are well structured and represent a valid discussion. However, this fact only becomes a meaningful debate within the context of a static or present Universe. As theoretically and observationally well established, the current Universe is undergoing accelerated expansion, wherein dimensional quantities, like the wavelength of light, also experience redshift phenomena elongating over cosmic time. In other words, in an expanding Universe, dimensional quantities of physical parameters vary with cosmic time. From this perspective, there exists the possibility that dimensional constants, such as the speed of light, could vary with the expansion of the Universe. In this review paper, we contemplate under what circumstances the speed of light may change or remain constant over cosmic time and discuss the potential for distinguishing these cases observationally.

]]>Particles doi: 10.3390/particles7020018

Authors: Serge Parnovsky

We consider the hypothesis that the sources of dark energy (DE) could be black holes (BHs) or more exotic objects, such as naked singularities or gravastars. We propose a definition of the presence of DE in the Universe and a criterion for what can be considered the source of this dark energy. It is based on the idea of the accelerated expansion of the Universe, which requires antigravity caused by large negative pressure. A recently proposed hypothesis, that the mass of BHs increases with time according to the same law as the volume of the part of the Universe containing it and the population of BHs can mimic DE, is examined. We demonstrate the reasons why it cannot be accepted, even if all the assumptions on which this hypothesis is based are considered true.

]]>Particles doi: 10.3390/particles7020017

Authors: Lorenzo Gallerani Resca

I consider the electro-weak (EW) masses and interactions generated by photons using vacuum expectation values of Stueckelberg and Higgs fields. I provide a prescription to relate their parametric values to a cosmological range derived from the fundamental Heisenberg uncertainty principle and the Einstein&ndash;de Sitter cosmological constant and horizon. This yields qualitative connections between microscopic ranges acquired by W&plusmn; or Z0 gauge Bosons and the cosmological scale and minimal mass acquired by g-photons. I apply this procedure to an established Stueckelberg&ndash;Higgs mechanism, while I consider a similar procedure for a pair of Higgs fields that may spontaneously break all U(1) &times; SU(2) gauge invariances. My estimates of photon masses and their additional parity-breaking interactions with leptons and neutrinos may be detectable in suitable accelerator experiments. Their effects may also be observable astronomically through massive g-photon condensates that may contribute to dark matter and dark energy.

]]>Particles doi: 10.3390/particles7010016

Authors: Mihaela-Andreea Băloi Cosmin Crucean Diana Dumitrele

The production of Z bosons in emission processes by neutrinos in the expanding de Sitter universe is studied by using perturbative methods. The total probability and transition rate for the spontaneous emission of a Z boson by a neutrino is computed analytically; then, we conduct a graphical analysis in terms of the expansion parameter. Our results prove that this process is possible only for large expansion conditions of the early universe. Finally, the density number of Z bosons is defined, and we obtain a quantitative estimation of this quantity in terms of the density number of neutrinos.

]]>Particles doi: 10.3390/particles7010015

Authors: Alessandro Curcio Alessandro Cianchi Massimo Ferrario

In this article, we highlight that the interaction potential confining Dirac particles in a box must be invariant under the charge conjugation to avoid the Klein paradox, in which an infinite number of negative-energy particles are excited. Furthermore, we derive the quantization rules for a relativistic particle in a cylindrical box, which emulates the volume occupied by a beam of particles with a non-trivial aspect ratio. We apply our results to the evaluation of the quantum limit for emittance in particle accelerators. The developed theory allows the description of quantum beams carrying Orbital Angular Momentum (OAM). We demonstrate how the degeneracy pressure is such to increase the phase&ndash;space area of Dirac particles carrying OAM. The results dramatically differ from the classical evaluation of phase&ndash;space areas, that would foresee no increase in emittance for beams in a coherent state of OAM. We discuss the quantization of the phase&ndash;space cell&rsquo;s area for single Dirac particles carrying OAM, and, finally, provide an interpretation of the beam entropy as the measure of how much the phase&ndash;space area occupied by the beam deviates from its quantum limit.

]]>Particles doi: 10.3390/particles7010014

Authors: Chuan-Xin Cui Jin-Yang Li Shinya Matsuzaki Mamiya Kawaguchi Akio Tomiya

The violation of the U(1) axial symmetry in QCD is stricter than the chiral SU(2) breaking simply because of the presence of the quantum axial anomaly. If the QCD gauge coupling is sent to zero (the asymptotic free limit, where the U(1) axial anomaly does not exist), the strength of the U(1) axial breaking coincides with that of the chiral SU(2) breaking, which we, in short, call an axial&ndash;chiral coincidence. This coincidence is trivial since QCD then becomes a non-interacting theory. Actually, there exists another limit in the QCD parameter space, where an axial&ndash;chiral coincidence occurs even with nonzero QCD gauge coupling, which can be dubbed a nontrivial coincidence: it is the case with the massive light quarks (ml&ne;0) and the massless strange quark (ms=0) due to the flavor-singlet nature of the topological susceptibility. This coincidence is robust and tied to the anomalous chiral Ward&ndash;Takahashi identity, which is operative even at hot QCD. This implies that the chiral SU(2) symmetry is restored simultaneously with the U(1) axial symmetry at high temperatures. This simultaneous restoration is independent of ml(&ne;0) and, hence, is irrespective of the order of the chiral phase transition. In this paper, we discuss how the real-life QCD can be evolved from the nontrivial chiral&ndash;axial coincidence limit by working on a Nambu&ndash;Jona&ndash;Lasinio model with the U(1) axial anomaly contribution properly incorporated. It is shown that, at high temperatures, the large differences between the restorations of the chiral SU(2) symmetry and the U(1) axial symmetry for two light quarks and a sufficiently large current mass for the strange quark are induced by a significant interference of the topological susceptibility. Thus, the deviation from the nontrivial coincidence, which is monitored by the strange quark mass controlling the topological susceptibility, provides a new way of understanding the chiral SU(2) and U(1) axial breaking in QCD.

]]>Particles doi: 10.3390/particles7010013

Authors: Maria Patsyuk Timur Atovullaev Goran Johansson Dmitriy Klimanskiy Vasilisa Lenivenko Sergey Nepochatykh Eli Piasetzky

The fundamental theory of nuclear interactions, Quantum Chromodynamics (QCD), operates in terms of quarks and gluons at higher resolution. At low resolution the relevant degrees of freedom are nucleons. Two-nucleon Short-Range Correlations (SRC) help to interconnect these two descriptions. SRCs are temporary fluctuations of strongly interacting close pairs of nucleons. The distance between the two nucleons is comparable to their radii and their relative momenta are larger than the fermi sea level. According to the electron scattering experiments held in the last decade, SRCs have far-reaching impacts on many-body systems, the nucleon-nucleon interactions, and nuclear substructure. The modern experiments with ion beams and cryogenic liquid hydrogen target make it possible to study properties of the nuclear fragments after quasi-elastic knockout of a single nucleon or an SRC pair. Here we review the status and perspectives of the SRC program in so-called inverse kinematics at JINR (Dubna, Russia). The first SRC experiment at the BM@N spectrometer (2018) with 4 GeV/c/nucleon carbon beam has shown that detection of an intact 11B nucleus after interaction selects out the quasi-elastic knockout reaction with minimal contribution of initial- and final-state interactions. Also, 25 events of SRC-breakups showed agreement in SRC properties as known from electron beam experiments. The analysis of the second measurement of SRC at BM@N held in 2022 with an improved setup is currently ongoing. The SRC project at JINR moved to a new experimental area in 2023, where the next measurement is being planned in terms of experimental setup and physics goals.

]]>Particles doi: 10.3390/particles7010012

Authors: Şerban Mişicu

The shape vibrations of a superheavy nucleus with a complete (bubble) or a partially (semi-bubble) depleted density in its central region and sharp-edge inner and outer surfaces are investigated in the frame of the Liquid-Drop Model. The quadrupole oscillations of the two existing surfaces are coupled in both velocity and coordinate and, upon decoupling, a low-energy and a high-energy component are predicted. The electric transition probabilities are estimated for the decay of the low-lying mode first 2+ state to the ground state for the entire range of the radius and density of the depleted core.

]]>Particles doi: 10.3390/particles7010011

Authors: Davood Rafiei Karkevandi Mahboubeh Shahrbaf Soroush Shakeri Stefan Typel

The presence of dark matter (DM) within neutron stars (NSs) can be introduced by different accumulation scenarios in which DM and baryonic matter (BM) may interact only through the gravitational force. In this work, we consider asymmetric self-interacting bosonic DM, which can reside as a dense core inside the NS or form an extended halo around it. It is seen that depending on the boson mass (m&chi;), self-coupling constant (&lambda;) and DM fraction (F&chi;), the maximum mass, radius and tidal deformability of NSs with DM admixture will be altered significantly. The impact of DM causes some modifications in the observable features induced solely by the BM component. Here, we focus on the widely used nuclear matter equation of state (EoS) called DD2 for describing NS matter. We show that by involving DM in NSs, the corresponding observational parameters will be changed to be consistent with the latest multi-messenger observations of NSs. It is seen that for m&chi;&#8819;200 MeV and &lambda;&#8818;2&pi;, DM-admixed NSs with 4%&#8818;F&chi;&#8818;20% are consistent with the maximum mass and tidal deformability constraints.

]]>Particles doi: 10.3390/particles7010010

Authors: Edoardo Giangrandi Afonso Ávila Violetta Sagun Oleksii Ivanytskyi Constança Providência

We investigate the impact of asymmetric fermionic dark matter (DM) on the thermal evolution of neutron stars (NSs), considering a scenario where DM interacts with baryonic matter (BM) through gravity. Employing the two-fluid formalism, our analysis reveals that DM accrued within the NS core exerts an inward gravitational pull on the outer layers composed of BM. This gravitational interaction results in a noticeable increase in baryonic density within the core of the NS. Consequently, it strongly affects the star&rsquo;s thermal evolution by triggering the early onsets of the direct Urca (DU) processes, causing enhanced neutrino emission and rapid star cooling. Moreover, the photon emission from the star&rsquo;s surface is modified due to a reduction in radius. We demonstrate the effect of DM gravitational pull on nucleonic and hyperonic DU processes that become kinematically allowed even for NSs of low mass. We then discuss the significance of observing NSs at various distances from the Galactic center. Given that the DM distribution peaks toward the Galactic center, NSs within this central region are expected to harbor higher fractions of DM, potentially leading to distinct cooling behaviors.

]]>Particles doi: 10.3390/particles7010009

Authors: Francesco Loparco

Flavour changing neutral current (FCNC) processes are described by loop diagrams in the Standard Model (SM), while in 331 models, based on the gauge group SU(3)C&times;SU(3)L&times;U(1)X, they are dominated by tree-level exchanges of a new heavy neutral gauge boson Z&prime;. By exploiting this feature, observables related to FCNC decays of K, Bd and Bs mesons can be considered in several variants of 331 models. The variants are distinguished by the value of a parameter &beta; that plays a key role in this framework. Imposing constraints on the &Delta;F=2 observables, we select possible ranges for the mass of the Z&prime; boson in correspondence to the values &beta;=&plusmn;k/3, with k=1,2. The results are used to determine the impact of 331 models on b&rarr;s processes and on the correlations among them, in the light of new experimental data recently released.

]]>Particles doi: 10.3390/particles7010008

Authors: Ruth Gregory Shi-Qian Hu

Higher derivative terms in the gravitational action are natural from the perspective of quantum gravity, but are perceived as leading to a lack of well-posedness. The Gauss&ndash;Bonnet term has second-order equations of motion, but does not impact gravitational dynamics in 4D, so one might expect that it is not physically relevant. We discuss how signatures can show up in tunnelling processes and whether these will likely be physically accessible in Higgs vacuum decay.

]]>Particles doi: 10.3390/particles7010007

Authors: Matteo Passet Mario Panelli Francesco Battista

The erosion of the accelerating chamber walls is one of the main factors limiting the operational life of Hall effect thrusters (HETs), and it is mainly related to the sputtering of ceramic walls due to the impacting energetic ion particles. The erosion phenomenon is investigated by means of a numerical model that couples the plasma model HYPICFLU2, used for evaluating the local distributions of ion energies and incidence angles, and a sputtering model specific for the xenon&ndash;Borosil pair, which is the most used in HETs application. The sputtering yield model is based on the measurements by Ranjan et al. that are improved with a linear factor to include wall temperature effect, recently studied by Parida et al. The experimental eroded profiles of SPT100 walls are selected as benchmark. The results show that there is a decrease in erosion speed with time, in accordance with experimental measurements, but the model underestimates, by about 50&ndash;60%, the erosion at the channel exit, which suggests a stronger dependence of sputter yield on surface temperature. Thus, the need for new experimental measurements of sputtering in the range of impact energy, angle, and wall temperature, respectively, of 10&ndash;250 eV, 0&ndash;85&deg;, 30&ndash;600 &deg;C, arises.

]]>Particles doi: 10.3390/particles7010006

Authors: J. D. Vergados S. Cohen F. T. Avignone R. Creswick

Axions can be considered as good dark matter candidates. The detection of such light particles can be achieved by observing axion-induced atomic excitations. The target is in a magnetic field so that the m-degeneracy is removed, and the energy levels can be suitably adjusted. Using an axion-electron coupling indicated by the limit obtained by the Borexino experiment, which is quite stringent, reasonable axion absorption rates have been obtained for various atomic targets The obtained results depend, of course, on the atom considered through the parameters &#1013; (the spin&minus;orbit splitting) as well as &delta; ( the energy splitting due to the magnetic moment interaction). This assumption allows axion masses in the tens of &mu;eV if the transition occurs between members of the same multiplet, i.e., |J1,M1=&minus;J1&#10217;&rarr;|J1,M1=&minus;J+1&#10217;,J1&ne;0, and axion masses in the range 1 meV&ndash;1 eV for transitions of the spin&minus;orbit splitting type |J1,M=&minus;J1&#10217;&rarr;|J2,M2=&minus;J1+q&#10217;,q=&minus;1,0,1, i.e., three types of transition. The axion mass that can be detected is very close to the excitation energy involved, which can vary by adjusting the magnetic field. Furthermore, since the axion is absorbed by the atom, the calculated cross-section exhibits the behavior of a resonance, which can be exploited by experiments to minimize any background events.

]]>Particles doi: 10.3390/particles7010005

Authors: Prashant Thakur Tuhin Malik Tarun Kumar Jha

Over the last few years, researchers have become increasingly interested in understanding how dark matter affects neutron stars, helping them to better understand complex astrophysical phenomena. In this paper, we delve deeper into this problem by using advanced machine learning techniques to find potential connections between dark matter and various neutron star characteristics. We employ Random Forest classifiers to analyze neutron star (NS) properties and investigate whether these stars exhibit characteristics indicative of dark matter admixture. Our dataset includes 32,000 sequences of simulated NS properties, each described by mass, radius, and tidal deformability, inferred using recent observations and theoretical models. We explore a two-fluid model for the NS, incorporating separate equations of state for nucleonic and dark matter, with the latter considering a fermionic dark matter scenario. Our classifiers are trained and validated in a variety of feature sets, including the tidal deformability for various masses. The performance of these classifiers is rigorously assessed using confusion matrices, which reveal that NS with admixed dark matter can be identified with approximately 17% probability of misclassification as nuclear matter NS. In particular, we find that additional tidal deformability data do not significantly improve the precision of our predictions. This article also delves into the potential of specific NS properties as indicators of the presence of dark matter. Radius measurements, especially at extreme mass values, emerge as particularly promising features. The insights gained from our study are pivotal for guiding future observational strategies and enhancing the detection capabilities of dark matter in NS. This study is the first to show that the radii of neutron stars at 1.4 and 2.07 solar masses, measured using NICER data from pulsars PSR J0030+0451 and PSR J0740+6620, strongly suggest that the presence of dark matter in a neutron star is more likely than only hadronic composition.

]]>Particles doi: 10.3390/particles7010004

Authors: Cédric Jockel Laura Sagunski

Dark matter could accumulate around neutron stars in sufficient amounts to affect their global properties. In this work, we study the effect of a specific model for dark matter&mdash;a massive and self-interacting vector (spin-1) field&mdash;on neutron stars. We describe the combined systems of neutron stars and vector dark matter using Einstein&ndash;Proca theory coupled to a nuclear matter term and find scaling relations between the field and metric components in the equations of motion. We construct equilibrium solutions of the combined systems, compute their masses and radii, and also analyze their stability and higher modes. The combined systems admit dark matter (DM) core and cloud solutions. Core solutions compactify the neutron star component and tend to decrease the total mass of the combined system. Cloud solutions have the inverse effect. Electromagnetic observations of certain cloud-like configurations would appear to violate the Buchdahl limit. This could make Buchdahl-limit-violating objects smoking gun signals for dark matter in neutron stars. The self-interaction strength is found to significantly affect both mass and radius. We also compare fermion Proca stars to objects where the dark matter is modeled using a complex scalar field. We find that fermion Proca stars tend to be more massive and geometrically larger than their scalar field counterparts for equal boson masses and self-interaction strengths. Both systems can produce degenerate masses and radii for different amounts of DM and DM particle masses.

]]>Particles doi: 10.3390/particles7010003

Authors: Turlan Sadykov Rauf Mukhamedshin Vladimir Galkin Alia Argynova Aidana Almenova Korlan Argynova Khanshaiym Makhmet Olga Novolodskaya Tunyk Idrissova Valery Zhukov Vyacheslav Piscal Zhakypbek Sadykov

In high-altitude experiments to study the central cores of EAS at E0 &#8819; 1016 eV (&radic;s &#8819; 5 TeV) using X-ray emulsion chambers and ionization calorimeters, phenomena such as the coplanarity of the arrival of the most energetic particles in super families of &gamma;-rays and hadrons and a so-called Tien Shan effect (too slow absorption of cascades initiated by high-energy hadrons in the calorimeter) were observed. These effects could not be reproduced within the framework of theoretical models of the 80s and 90s. The coplanarity is explained via a process of coplanar generation of the most energetic secondary particles in interactions of super high-energy hadrons with nuclei of air atoms. Perhaps the Tien Shan effect could be explained using a high cross section for the generation of fragmentation-region charmed hadrons. To study these phenomena, a new set of detectors has been developed, including the world&rsquo;s highest high-mountain ionization calorimeter, &ldquo;Hadron-55&rdquo;. This paper presents the initial experimental results.

]]>Particles doi: 10.3390/particles7010002

Authors: Manfried Faber

We describe particles in a potential by a special diffusion process, the maximal entropy random walk (MERW) on a lattice. Since MERW originates in a variational problem, it shares the linear algebra of Hilbert spaces with quantum mechanics. The Born rule appears from measurements between equilibrium states in the past and the same equilibrium states in the future. Introducing potentials by the observation that time, in a gravitational field running in different heights with a different speed, MERW respects the rule that all trajectories of the same duration are counted with equal probability. In this way, MERW allows us to derive the Schr&ouml;dinger equation for a particle in a potential and the Darwin term of the nonrelativistic expansion of the Dirac equation. Finally, we discuss why quantum mechanics cannot be simply a result of MERW, but, due to the many analogies, MERW may pave the way for further understanding.

]]>Particles doi: 10.3390/particles7010001

Authors: Gustavo García Marcelo Salgado Philippe Grandclément Eric Gourgoulhon

First, we review the solutions of a complex-valued scalar field, termed scalar clouds, with and without electric charge, when coupled to a rotating Kerr&ndash;Newman (electrically charged) or Kerr (neutral) black hole (BH), respectively. To this aim, we determine the conditions and parameters that characterize the existence of solutions that represent bound states, with an energy-momentum tensor that respect the symmetries of the underlying spacetimes, even if the backreaction of the field is not taken into account at this stage. In particular, we show that in the extremal Kerr scenario the cloud solutions exist only when the mass of the BH satisfies certain bounds, which are obtained by analyzing an effective potential associated with the radial dependency of the scalar clouds that leads to a Schr&ouml;dinger-like equation. Second, when the backreaction of the field in the spacetime is taken into account, we present a family of stationary, axisymmetric and asymptotically flat solutions of the Einstein&ndash;Klein&ndash;Gordon system that represent genuine rotating hairy black holes (RHBHs) and provide different values of some global quantities associated with them, such as the Komar mass and the Komar angular momentum. We also compute RHBH solutions with nodes in the radial part of the scalar field and also for a higher azimuthal number m.

]]>Particles doi: 10.3390/particles6040063

Authors: Igor Kondrashuk Ivan Schmidt

We argue in favor of the independence on any scale, ultraviolet or infrared, in kernels of the effective action expressed in terms of dressed N=1 superfields for the case of N=4 super-Yang&ndash;Mills theory. Under &ldquo;scale independence&rdquo; of the effective action of dressed mean superfields, we mean its &ldquo;finiteness in the off-shell limit of removing all the regularizations&rdquo;. This off-shell limit is scale independent because no scale remains inside these kernels after removing the regularizations. We use two types of regularization: regularization by dimensional reduction and regularization by higher derivatives in its supersymmetric form. Based on the Slavnov&ndash;Taylor identity, we show that dressed fields of matter and of vector multiplets can be introduced to express the effective action in terms of them. Kernels of the effective action expressed in terms of such dressed effective fields do not depend on the ultraviolet scale. In the case of dimensional reduction, by using the developed technique, we show how the problem of inconsistency of the dimensional reduction can be solved. Using Piguet and Sibold formalism, we indicate that the dependence on the infrared scale disappears off shell in both the regularizations.

]]>Particles doi: 10.3390/particles6040062

Authors: Marcos Cardoso Rodriguez Ion Vasile Vancea

In this article, we give a brief review of the origin of the neutrino mass in some interesting non-linear supersymmetric models with R-symmetry. These models are able to address and solve the most important problems of particle physics and provide mechanisms for neutrino mass generation and their mixing parameters in agreement with the current experimental data. Their prediction could be experimentally tested in the near future by collider experiments.

]]>Particles doi: 10.3390/particles6040061

Authors: Adam R. Solomon

We explore the duality invariance of the Maxwell and linearized Einstein&ndash;Hilbert actions on a non-rotating black hole background. On-shell, these symmetries are electric&ndash;magnetic duality and Chandrasekhar duality, respectively. Off-shell, they lead to conserved quantities; we demonstrate that one of the consequences of these conservation laws is that even- and odd-parity metric perturbations have equal Love numbers. Along the way, we derive an action principle for the Fackerell&ndash;Ipser equation and Teukolsky&ndash;Starobinsky identities in electromagnetism.

]]>Particles doi: 10.3390/particles6040060

Authors: Athanasios C. Tzemos George Contopoulos

We study order, chaos and ergodicity in the Bohmian trajectories of a 2D quantum harmonic oscillator. We first present all the possible types (chaotic, ordered) of Bohmian trajectories in wavefunctions made of superpositions of two and three energy eigenstates of the oscillator. There is no chaos in the case of two terms and in some cases of three terms. Then, we show the different geometries of nodal points in bipartite Bohmian systems of entangled qubits. Finally, we study multinodal wavefunctions and find that a large number of nodal points does not always imply the dominance of chaos. We show that, in some cases, the Born distribution is dominated by ordered trajectories, something that has a significant impact on the accessibility of Born&rsquo;s rule P=|&Psi;|2 by initial distributions of Bohmian particles with P0&ne;|&Psi;0|2.

]]>Particles doi: 10.3390/particles6040059

Authors: Alexei A. Deriglazov

We single out a class of Lagrangians on a group manifold, for which one can introduce non-canonical coordinates in the phase space, which simplify the construction of the Poisson structure without explicitly calculating the Dirac bracket. In the case of the SO(3) manifold, the application of this formalism leads to the Poincar&eacute;&ndash;Chetaev equations. The general solution to these equations is written in terms of an exponential of the Hamiltonian vector field.

]]>Particles doi: 10.3390/particles6040058

Authors: Supachai Prawanta Prapaiwan Sunwong Pariwat Singthong Thongchai Leetha Pajeeraphorn Numanoy Warissara Tangyotkhajorn Apichai Kwankasem Visitchai Sooksrimuang Sukho Kongtawong Supat Klinkiew

A prototype of a combined horizontal and vertical correcting magnet was designed and fabricated for the 3 GeV storage ring of Siam Photon Source II, which will be the second synchrotron light source in Thailand. The magnet will be employed for fast-orbit feedback correction, with a required magnetic field integral of approximately 8 Tesla.mm. The magnet pole and yoke were manufactured using laminated silicon steel to minimize hysteresis and eddy current losses during operation. Magnet modeling and magnetic field calculations were performed using Opera-3D. The size of the gap between the magnet poles is limited by the size of the vacuum chamber over which the magnet will be installed; in this case, it was designed to be 65 mm. Mechanical analysis of the structure of the magnet was performed using SOLIDWORKS and ANSYS. Magnetic field measurements were obtained using the Hall probe technique. The entire prototype, from its design to manufacturing and measurement, was completed in-house. This design will be appropriate for application at the Siam Photon Source II storage ring.

]]>Particles doi: 10.3390/particles6040057

Authors: Yernur Kuanyshbaiuly Ardak Junissov Mukhit Muratov

We have studied wake effects on the dissociation of heavy quarkonia states&nbsp;J/&psi;&nbsp;and&nbsp;Y&nbsp;by introducing an in-medium modification to the inter-quark potential. The wakes in the quark&ndash;gluon plasma were modeled using linear response theory using a dynamic dielectric function obtained from kinetic theory (Boltzmann equation) with a Bhatnagar&ndash;Gross&ndash;Krook (BGK) collision term. The in-medium modified potential was used to investigate the dissociation character depending on various parameters such as the velocity of quarkonium moving through the medium and the collision frequency. We have also calculated critical values of the dissociation temperature. Modifications of the dissociation energy due to wake-field effects were found.

]]>Particles doi: 10.3390/particles6040056

Authors: Alexandra Friesen Yuriy Kalinovsky

The applicability of the effective models to the description of baryons and the behaviour of ratios of strange baryons to pions is discussed. In the framework of the EPNJL model, the Bethe&ndash;Salpeter equation is used to find masses of baryons, which are considered to be in a diquark-quark state. Baryon melting is discussed at a finite chemical potential, and a flavor dependence of the hadronic deconfinement temperature is pointed out. It is shown that the description of the diquark-quark state at finite chemical potential is limited due to the occurrence of Bose condensate. This effect is strongly manifested in the description of light diquarks and baryons. Both the &Lambda;0/&pi;+ and &Xi;&minus;/&pi;+ ratios show a sharp behaviour as functions of the T/&mu;B variable, where T and &mu;B are calculated along the melting lines.

]]>Particles doi: 10.3390/particles6030055

Authors: Maksym Teslyk Olena Teslyk Larissa Bravina Evgeny Zabrodin

The entropy produced by Unruh radiation is estimated and compared to the entropy of a Schwarzschild black hole. We simulate a spherical system of mass M by a set of Unruh horizons and estimate the total entropy of the outgoing radiation. Dependence on the mass and spin of the emitted particles is taken into account. The obtained results can be easily extended to any other intrinsic degrees of freedom of outgoing particles. The ratio of Unruh entropy to the Schwarzschild black hole entropy is derived in exact analytical form. For large black holes, this ratio exhibits high susceptibility to quantum numbers, e.g., spin s, of emitted quanta and varies from 0% for s=0 to 19.0% for s=5/2.

]]>Particles doi: 10.3390/particles6030054

Authors: Semyon Mikheev Dmitry Lanskoy Artur Nasakin Tatiana Tretyakova

The matter of neutron stars is characterised by the density of the order of typical nuclear densities; hence, it can be described with methods of nuclear physics. However, at high densities, some effects that are absent in nuclear and hypernuclear physics can appear, and this makes neutron stars a good place for studying the properties of baryonic interactions. In the present work, we consider neutron stars consisting of nucleons, leptons and &Lambda; hyperons with Skyrme baryonic forces. We study the character of the &Lambda;N interactions taking place in neutron stars at high densities. In particular, we show the difference between three-body &Lambda;NN and density-dependent &Lambda;N forces. We also demonstrate that the Skyrme &Lambda;N forces proportional to nuclear density are better suited for the modelling of neutron stars than the forces proportional to fractional powers of density. Finally, we emphasize the importance of the point of appearance of hyperons in a further search for parameterizations which are suitable for describing neutron stars.

]]>Particles doi: 10.3390/particles6030053

Authors: Nikolai Gerasimeniuk Vitaly Bornyakov Vladimir Goy Roman Rogalyov Anatolii Korneev Alexander Molochkov Atsushi Nakamura

We compute the canonical partition functions and the Lee&ndash;Yang zeros in Nf=2 lattice QCD at temperature T=1.20Tc lying above the Roberge&ndash;Weiss phase transition temperature TRW. The phase transition is characterized by the discontinuities in the baryon number density at specific values of imaginary baryon chemical potential. We further develop our method to compute the canonical partition functions using the asymptotic expression for respective integral. Then, we compute the Lee&ndash;Yang zeros and study their behavior in the limit of high baryon density.

]]>Particles doi: 10.3390/particles6030052

Authors: Serge Parnovsky

We investigate possible astronomical manifestations of space-time anisotropy. The homogeneous vacuum Kasner solution was chosen as a reference anisotropic cosmological model because there are no effects caused by inhomogeneity in this simple model with a constant degree of anisotropy. This anisotropy cannot become weak. The study of its geodesic structure made it possible to clarify the properties of this space-time. It showed that the degree of manifestation of anisotropy varies significantly depending on the travel time of the light from the observed object. For nearby objects, for which it does not exceed half the age of the universe, the manifestations of anisotropy are very small. Distant objects show more pronounced manifestations; for example, in the distribution of objects over the sky and over photometric distances. These effects for each of the individual objects decrease with time but, in general, the manifestations of anisotropy in the Kasner space-time remain constant due to the fact that new sources come from beyond the cosmological horizon. We analyze observable signatures of the Kasner-type anisotropy and compare it to observations. These effects were not found in astronomical observations, including the study of the CMB. We can assume that the Universe has always been isotropic or almost isotropic since the recombination era. This does not exclude the possibility of its significant anisotropy at the moment of the Big Bang followed by rapid isotropization during the inflationary epoch.

]]>Particles doi: 10.3390/particles6030051

Authors: Marco Arcani Domenico Liguori Andrea Grana

Cosmic ray air showers are a phenomenon that can be observed on Earth when high-energy particles from outer space collide with the Earth&rsquo;s atmosphere. These energetic particles in space are called primary cosmic rays and consist mainly of protons (about 89%), along with nuclei of helium (10%) and heavier nuclei (1%). Particles resulting from interactions in the atmosphere are called secondary cosmic rays. The composition of air showers in the atmosphere can include several high-energy particles such as mesons, electrons, muons, photons, and others, depending on the energy and type of the primary cosmic ray. Other than air, primary cosmic rays can also produce showers of particles when they interact with any type of matter; for instance, particle showers are also produced within the soil of planets without an atmosphere. In the same way, secondary cosmic particles can start showers of tertiary particles in any substance. In the 1930s, Bruno Rossi conducted an experiment to measure the energy loss of secondary cosmic rays passing through thin metal sheets. Surprisingly, he observed that as the thickness of the metal sheets increased, the number of particles emerging from the metal also increased. However, by adding more metal sheets, the number of particles eventually decreased. This was consistent with the expectation that cosmic rays were interacting with the atoms in the metals and losing energy to produce multiple secondary particles. In this paper, we describe a new&ndash;old approach for measuring particle showers in water using a cosmic ray telescope and Rossi&rsquo;s method. Our instrument consists of four Geiger&ndash;M&uuml;ller tubes (GMT) arranged to detect muons and particle showers. GMT sensors are highly sensitive devices capable of detecting electrons and gamma rays with energies ranging from a few tens of keV up to several tens of MeV. Since Rossi studied the effects caused by cosmic rays as they pass through metals, we wondered if the same process could also happen in water. We present results from a series of experiments conducted with this instrument, demonstrating its ability to detect and measure particle showers produced by the interaction of cosmic rays in water with good confidence. To the best of our knowledge, this experiment has never been conducted before. Our approach offers a low-cost and easy-to-use alternative to more sophisticated cosmic ray detectors, making it accessible to a wider range of researchers and students.

]]>Particles doi: 10.3390/particles6030050

Authors: Andrey Yudin Nikita Kramarev Igor Panov Anton Ignatovskiy

We investigate the impact of forthcoming nuclear data on the predictions of the neutron star (NS) stripping model for short gamma-ray bursts. The main area to which we pay attention is the NS crust. We show that the uncertain properties of the NS equation of state can significantly influence the stripping time tstr, the main dynamical parameter of the model. Based on the known time delay (tstr&asymp;1.7 s) between the peak of the gravitational wave signal GW170817 and the detection of gamma photons from GRB170817A, we obtain new restrictions on the nuclear matter parameters, in particular, the symmetry energy slope parameter: L&lt;114.5MeV. In addition, we study the process of nucleosynthesis in the outer and inner crusts of a low-mass NS. We show that the nucleosynthesis is strongly influenced by both the forthcoming nuclear data and the equation of state of the NS matter.

]]>Particles doi: 10.3390/particles6030049

Authors: Roman Rogalyov Vladimir Goy

We use the results of lattice simulations of the net-baryon number density at imaginary baryon chemical potential in Nf=2 QCD to construct the equation of state of dense and hot strong-interacting matter both above the Roberge&ndash;Weiss temperature T&gt;TRW and below the critical temperature T&lt;Tc. For these cases, we also evaluate probability distributions of the net-baryon number, as well as the respective cumulants and moments. The consequences of the asymptotic behavior of these probability distributions for the problem of reconstruction of the net-baryon probability distributions from cumulants are discussed.

]]>Particles doi: 10.3390/particles6030048

Authors: Antonio Gallerati

We review some recent soliton solutions in a class of four-dimensional supergravity theories. The latter can be obtained from black hole solutions by means of a double Wick rotation. For special values of the parameters, the new configurations can be embedded in the gauged maximal N=8 theory and uplifted in the higher-dimensional D=11 theory. We also consider BPS soliton solutions, preserving a certain fraction of supersymmetry.

]]>Particles doi: 10.3390/particles6030047

Authors: Richard S. Garavuso

In this paper, we discuss various aspects of a class of A-twisted heterotic Landau&ndash;Ginzburg models on a K&auml;hler variety X. We provide a classification of the R-symmetries in these models which allow the A-twist to be implemented, focusing on the case in which the gauge bundle is either a deformation of the tangent bundle of X or a deformation of a sub-bundle of the tangent bundle of X. Some anomaly-free examples are provided. The curvature constraint imposed by supersymmetry in these models when the superpotential is not holomorphic is reviewed. Constraints of this nature have been used to establish properties of analogues of pullbacks of Mathai&ndash;Quillen forms which arise in the correlation functions of the corresponding A-twisted or B-twisted heterotic Landau&ndash;Ginzburg models. The analogue most relevant to this paper is a deformation of the pullback of a Mathai&ndash;Quillen form. We discuss how this deformation may arise in the class of models studied in this paper. We then comment on how analogues of pullbacks of Mathai&ndash;Quillen forms not discussed in previous work may be obtained. Standard Mathai&ndash;Quillen formalism is reviewed in an appendix. We also include an appendix which discusses the deformation of the pullback of a Mathai&ndash;Quillen form.

]]>Particles doi: 10.3390/particles6030046

Authors: Shimon Yamada Shigeru Kashiwagi Ikuro Nagasawa Ken-ichi Nanbu Toshiya Muto Ken Takahashi Ken Kanomata Kotaro Shibata Fujio Hinode Sadao Miura Hiroki Yamada Kohei Kumagai Hiroyuki Hama

A test-Accelerator as Coherent Terahertz Source (t-ACTS) has been under development at Tohoku University, in which an intense coherent terahertz radiation is generated from the short electron bunches. Velocity bunching scheme in a traveling wave accelerating structure is employed to generate the short electron bunches. The in-phase and quadrature (IQ) modulator and demodulator were installed to the low-level RF systems of t-ACTS linac to control and measure the amplitude and phase of RF power. The amplitude and phase of the RF power applied to an RF electron gun cavities and the accelerating structure are controlled to produce the electron bunches with a uniform and small momentum spread suitable for the velocity bunching. By installing the feed-forward control system using IQ modulators for the beam conditioning, we have successfully generated flat RF pulses and improved beam quality, including the energy spectrum of the beam. The details of feed-forward control system of the amplitude and phase using the IQ modulator and the beam experiments are presented in this paper.

]]>Particles doi: 10.3390/particles6030045

Authors: Matteo Breschi Gregorio Carullo Sebastiano Bernuzzi

Gravitational waves from binary neutron star (BNS) mergers can constrain nuclear models, predicting their equation of state (EOS). Matter effects on the inspiral-merger signal are encoded in the multipolar tidal polarizability parameters, whose leading order combination is sufficient to capture, with high accuracy, the key features of the merger waveform. Similar EOS-insensitive relations exist for the post-merger signal and can be used to model the emissions from the remnant. Several works suggested that the appearance of new degrees of freedom in high-density post-merger matter can be inferred by observing a violation of these EOS-insensitive relations. Here, we demonstrate a Bayesian method to test such an EOS-insensitive relation between the tidal polarizability parameters (or any other equivalent parameter) and the dominant post-merger frequency using information from the pre-and-post-merger signal. Technically, the method is similar to the inspiral-merger-ringdown consistency tests of General Relativity with binary black holes. However, differently from the latter, BNS pre/post-merger consistency tests are conceptually less informative and they only address the consistency of the assumed EOS-insensitive relation. Specifically, we discuss how such tests cannot conclusively discriminate between an EOS without respecting such a relation and the appearance of new degrees of freedom (or phase transitions) in high-density matter.

]]>Particles doi: 10.3390/particles6030044

Authors: Armen Sedrakian

This review covers several recent developments in the physics of dense QCD with an emphasis on the impact of multiple phase transitions on astrophysical manifestations of compact stars. To motivate the multi-phase modeling of dense QCD and delineate the perspectives, we start with a discussion of the structure of its phase diagram and the arrangement of possible color-superconducting and other phases. It is conjectured that pair-correlated quark matter in &beta;-equilibrium is within the same universality class as spin-imbalanced cold atoms and the isospin asymmetrical nucleonic matter. This then implies the emergence of phases with broken space symmetries and tri-critical (Lifshitz) points. The beyond-mean-field structure of the quark propagator and its non-trivial implications are discussed in the cases of two- and three-flavor quark matter within the Eliashberg theory, which takes into account the frequency dependence (retardation) of the gap function. We then construct an equation of state (EoS) that extends the two-phase EoS of dense quark matter within the constant speed of sound parameterization by adding a conformal fluid with a speed of sound cconf.=1/3 at densities &ge;10nsat, where nsat is the saturation density. With this input, we construct static, spherically symmetrical compact hybrid stars in the mass&ndash;radius diagram, recover such features as the twins and triplets, and show that the transition to conformal fluid leads to the spiraling-in of the tracks in this diagram. Stars on the spirals are classically unstable with respect to the radial oscillations but can be stabilized if the conversion timescale between quark and nucleonic phases at their interface is larger than the oscillation period. Finally, we review the impact of a transition from high-temperature gapped to low-temperature gapless two-flavor phase on the thermal evolution of hybrid stars.

]]>Particles doi: 10.3390/particles6030043

Authors: Kittipong Techakaew Kanlayaporn Kongmali Sakhorn Rimjaem

The linear accelerator system of the PBP-CMU Electron Linac Laboratory has been designed with the aim of generating free-electron lasers (FELs) in the mid-infrared (MIR) and terahertz (THz) regions. The quality of the radiation is strongly dependent on the properties of the electron beam. Among the important beam parameters, the electron beam energy and energy spread are particularly important. To accurately measure the electron beam energy, the first dipole magnet in the bunch compressor system and the downstream screen station are employed as an energy spectrometer. The A Space Charge Tracking Algorithm (ASTRA) software is used for the design and optimization of this system. Simulation results demonstrate that the developed spectrometer is capable of accurately measuring the energy within the 5&ndash;25 MeV range. The screen station system is designed and constructed to have the ability to capture a beam size with a resolution of 0.1 mm per pixel. This resolution is achieved with a screen-to-camera distance of 1.2 m, which proves sufficient for precise energy measurement. The systematic error in energy measurement is found to be less than 10%, with a minimum energy spread of 0.4% achievable when the horizontal beam size remains below 3 mm.

]]>Particles doi: 10.3390/particles6030042

Authors: Hiroki Yamada Toshiya Muto Fujio Hinode Shigeru Kashiwagi Ken-ichi Nanbu Ken Kanomata Ikuro Nagasawa Ken Takahashi Koutaro Shibata Hiroyuki Hama

Smith&ndash;Purcell radiation (SPR) can be generated nondestructively, providing valuable applications in light sources and beam monitors. Coherent SPR is expected to enable single-shot measurements of very short bunch lengths on the fs scale. Since the reconstruction of the longitudinal bunch shape from the coherent SPR is based on the reliable SPR spectrum, a more detailed understanding of the properties of the radiation is important in this context. Employing a 100 fs ultrashort electron bunch at the t-ACTS test accelerator, the spectrum, angular distribution, and polarization of the produced coherent SPR were measured in the terahertz frequency region and compared with a model calculation. In addition to the widely known surface current model evaluation, the effect of the geometrical shading effect on induced currents on metal surfaces was evaluated using 3D numerical calculations. The obtained SPR characteristics are also presented. In the evaluation of the grating with a shallow blaze angle, it was found that the shading effect has a non-negligible effect on the generated SPR intensity; the measured angular distribution and polarization results were in good agreement with this result.

]]>Particles doi: 10.3390/particles6030041

Authors: A. A. Dzhioev A. V. Yudin N. V. Dunina-Barkovskaya A. I. Vdovin

Applying TQRPA calculations of Gamow&ndash;Teller strength functions in hot nuclei, we compute the (anti)neutrino spectra and energy loss rates arising from weak processes on hot 56Fe under pre-supernova conditions. We use a realistic pre-supernova model calculated by the stellar evolution code MESA. Taking into account both charged and neutral current processes, we demonstrate that weak reactions with hot nuclei can produce high-energy (anti)neutrinos. We also show that, for hot nuclei, the energy loss via (anti)neutrino emission is significantly larger than that for nuclei in their ground state. It is found that the neutral current de-excitation via the &nu;&nu;&macr;-pair emission is presumably a dominant source of antineutrinos. In accordance with other studies, we confirm that the so-called single-state approximation for neutrino spectra might fail under certain pre-supernova conditions.

]]>Particles doi: 10.3390/particles6020040

Authors: Siriwan Jummunt Wanisa Promdee Thakonwat Chanwattana Nawin Junthong Somjai Chunjarean Supat Klinkhieo

An intense narrow-band terahertz (THz) radiation source has been designed to generate a broad tuning range of radiation frequencies between 0.5 THz and 5.0 THz. The THz radiation is produced when a short-bunch electron beam propagates through an undulator. To achieve high-power peak radiation, the source requires high-brightness electron beams with low beam emittance and short bunch length. A proposed design for the photocathode RF gun used as the electron source is presented. The gun with high mode separation and high Q-factor can be achieved for producing a good beam quality. The beam dynamics of the injector have been preliminarily optimized using the software ASTRA and Elegant, investigating the impact of laser pulse shape on electron beam quality. The results of the beam dynamics studies are comprehensively discussed in this paper.

]]>Particles doi: 10.3390/particles6020039

Authors: Supachai Prawanta Thongchai Leetha Pariwat Singthong Pajeeraphorn Numanoy Apichai Kwankasem Visitchai Sooksrimuang Chaiyut Preecha Supat Klinkiew Prapaiwan Sunwong

A prototype of a type A quadrupole magnet has been designed and manufactured for the 3 GeV storage ring of Siam Photon Source II, the second synchrotron light source in Thailand. The required quadrupole gradient is 51 T/m with the magnet effective length being 162 mm. Magnet modeling and magnetic field calculation were performed using Radia and Opera-3D. The bore radius of the magnet is 16 mm. The magnet will be operated at the excitation of 5544 A-turns. A mechanical analysis of the magnet structure was performed in SOLIDWORKS and ANSYS, where the maximum deformation of 0.003 mm was found at the magnet poles, and the first-mode natural frequency was higher than 100 Hz. The magnet yoke is made of AISI 1006 low-carbon steel with a fabrication tolerance of &plusmn;0.020 mm. Magnet coils are water-cooled and made of high-purity copper. The temperature rise of the coils was below 3.0 &deg;C at the maximum excitation of 6664 A-turns, which is 20% above the operating point. Magnetic field measurement was carried out using the Hall probe technique. The measured magnetic field and coil temperature of the prototype show good agreement with the calculations.

]]>Particles doi: 10.3390/particles6020038

Authors: Irina Dymnikova

We address the question of the electromagneticdensity and the mass function for regular rotating electrically charged compact objects as determined by dynamical equations of nonlinear electrodynamics minimally coupled to gravity. The rotating electrically charged compact objects are described by axially symmetric geometry, in which their electromagnetic fields are governed by four source-free equations for two independent field components of the electromagnetic tensor F&mu;&nu;, with two constraints on the integration functions. An additional condition of compatibility of four dynamical equations for two independent field functions imposes the constraint on the Lagrange derivative LF=dL/dF, directly related to the electromagnetic density. As a result, the compatibility condition determines uniquely the generic form of the electromagnetic density and the mass function for regular rotating electrically charged compact objects.

]]>Particles doi: 10.3390/particles6020037

Authors: Yuhao Zhao Heishun Zen Hideaki Ohgaki

A project is underway that aims to generate attosecond pulses via high-harmonic generation in rare gases, driven by extremely short and highly intense pulses from free-electron-laser oscillators. For this purpose, it has been planned that a new photocathode RF gun, dedicated to high-bunch-charge operation, will be installed at the KU-FEL (Kyoto University Free Electron Laser) oscillator facility. In this study, RF guns with two different structures (1.6-cell and 1.4-cell) were compared, from the perspective of exploring the possibility of introducing bunch-interval modulation, which is important for achieving high extraction efficiency in the FEL oscillator. As a result, it was confirmed that the introduction of bunch-phase modulation would be possible only in the case of the 1.6-cell RF gun. After the structure of the RF gun was decided on, particle-tracking simulations were performed, to study the electron-beam parameters using the 1.6-cell RF gun and 1 nC bunch charge. The results showed that we could obtain the peak current of 1 kA without a large degradation of the other parameters.

]]>Particles doi: 10.3390/particles6020036

Authors: Mikhail Mamaev Arkadiy Taranenko

The study of the high-density equation of state (EOS) and the search for a possible phase transition in dense baryonic matter is the main goal of beam energy scan programs with relativistic heavy ions at energies sNN= 2&ndash;5 GeV. The most stringent constraints currently available on the high-density EOS of symmetric nuclear matter come from the present measurements of directed (v1) and elliptic flow (v2) signals of protons in Au + Au collisions. In this energy range, the anisotropic flow is strongly affected by the presence of cold spectators due to the sizable passage time. The system size dependence of anisotropic flow may help to study the participant&ndash;spectator contribution and improve our knowledge of the EOS of symmetric nuclear matter. In this work, we discuss the layout of the upgraded BM@N experiment and the anticipated performance for differential anisotropic flow measurements of identified hadrons at Nuclotron energies: sNN= 2.3&ndash;3.5 GeV.

]]>Particles doi: 10.3390/particles6020035

Authors: Omar Benhar

Nuclear many-body theory is based on the tenet that nuclear systems can be accurately described as collections of point-like particles. This picture, while providing a remarkably accurate explanation of a wealth of measured properties of atomic nuclei, is bound to break down in the high-density regime, in which degrees of freedom other than protons and neutrons are expected to come into play. Valuable information on the validity of the description of dense nuclear matter in terms of nucleons, needed to firmly establish its limit of applicability, can be obtained from electron&ndash;nucleus scattering data at large momentum transfer and low energy transfer. The emergence of y-scaling in this kinematic region, unambiguously showing that the beam particles couple to high-momentum nucleons belonging to strongly correlated pairs, indicates that at densities as large as five times nuclear density&mdash;typical of the neutron star interior&mdash;nuclear matter largely behaves as a collection of nucleons.

]]>Particles doi: 10.3390/particles6020034

Authors: Sergei V. Sinitsyn

The analysis of fifty empirical period-radius relations and forty-three empirical period-luminosity relations is performed for the Cepheids. It is found that most of these relations have significant systematic errors. A new metrological method is suggested to exclude these systematic errors using the new empirical metrological relations and the empirical temperature scale of the various samples of the Cepheids. In this regard, the reliable relations between the mass, radius, effective surface temperature, luminosity, absolute magnitude on the one hand, and the pulsation period on the other hand, as well as the reliable dependence of the radius on the mass are determined for the Cepheids of types &delta; Cephei and &delta; Scuti from the Galaxy. These reliable relations permit us to accurately determine the empirical value of the pulsation constant for the Cepheids of both types for the first time. It is found that the pulsation constant very weakly depends on the pulsation period of the Cepheid, contrary to the known theoretical calculation. Hence, the Cepheids pulsate almost as a unified whole and homogeneous spherical body in wide ranges of a star&rsquo;s mass and evolutionary state with an extremely inhomogeneous distribution of stellar substance over its volume. Therefore, it is first suggested that the pulsation of the Cepheid is, first of all, the pulsation of the almost unified whole and homogenous shell of its gravitational mass. This pulsation is triggered by well-known effects; for example, the local optical opacity of the stellar substance and overshooting, using the usual pulsation of the stellar substance.

]]>Particles doi: 10.3390/particles6020033

Authors: Maxim A. Krasnov Valery V. Nikulin

Primordial black holes have become a highly intriguing and captivating field of study in cosmology due to their potential theoretical and observational significance. This review delves into a variety of mechanisms that could give rise to PBHs and explores various methods for examining their evolution through mass accretion.

]]>Particles doi: 10.3390/particles6020032

Authors: Ilya Segal

The size and evolution of the matter created in a relativistic heavy-ion collision strongly depend on collision geometry, defined by centrality. Experimentally the centrality of collisions can be characterized by the measured multiplicities of the produced particles at midrapidity or by the energy measured in the forward rapidity region, which is sensitive to the spectator fragments. This serves as a proxy for the true collision centrality, as defined by the impact parameter in the models of collisions. In this work, the procedure for centrality determination based on Monte-Carlo sampling of spectator fragments has been proposed. The validity of the procedure has been checked using the fully reconstructed DCM-QGSM-SMM model events and published data from the NA61/SHINE experiment.

]]>Particles doi: 10.3390/particles6020031

Authors: Keith Andrew Eric V. Steinfelds Kristopher A. Andrew

We explore the chemical potential of a QCD-motivated van der Waals (VDW) phase change model for the six-quark color-singlet, strangeness S = &minus;2 particle known as the hexaquark with quark content (uuddss). The hexaquark may have internal structure, indicated by short range correlations that allow for non-color-singlet diquark and triquark configurations whose interactions will change the magnitude of the chemical potential. In the multicomponent VDW Equation of State (EoS), the quark-quark particle interaction terms are sensitive to the QCD color factor, causing the pairing of these terms to give different interaction strengths for their respective contributions to the chemical potential. This results in a critical temperature near 163 MeV for the color-singlet states and tens of MeV below this for various mixed diquark and triquark states. The VDW chemical potential is also sensitive to the number density, leading to chemical potential isotherms that exhibit spinodal extrema, which also depend upon the internal hexaquark configurations. These extrema determine regions of metastability for the mixed states near the critical point. We use this chemical potential with the chemical potential-modified TOV equations to investigate the properties of hexaquark formation in cold compact stellar cores in beta equilibrium. We find thresholds for hexaquark layers and changes in maximum mass values that are consistent with observations from high mass compact stellar objects such as PSR 09043 + 10 and GW 190814. In general, we find that the VDW-TOV model has an upper stability mass and radius bound for a chemical potential of 1340 MeV with a compactness of C~0.2.

]]>Particles doi: 10.3390/particles6020030

Authors: Yuri Kharlov Yeghishe Hambardzumyan Antony Varlamov

Quarkonia represent one of the most valuable probes of the deconfined quark&ndash;gluon hot medium since the very first experimental studies with ultrarelativistic heavy-ion collisions. A significant step forward in characterizing the QCD matter via systematic studies of quarkonia production will be performed by the next-generation heavy-ion experiment ALICE 3, a successor of the ongoing ALICE experiment at the Large Hadron Collider. The new advanced detector of ALICE 3 will allow for exploring the production of S- and P-state quarkonia at high statistics, at low and moderate transverse momenta ranges. The performance of ALICE 3 for quarkonia measurements and the requirements for the detectors are discussed.

]]>Particles doi: 10.3390/particles6020029

Authors: Kai-Bao Chen Tianbo Liu Yu-Kun Song Shu-Yi Wei

The hadronization of a high-energy parton is described by fragmentation functions which are introduced through QCD factorizations. While the hadronization mechanism per se remains uknown, fragmentation functions can still be investigated qualitatively and quantitatively. The qualitative study mainly concentrates on extracting genuine features based on the operator definition in quantum field theory. The quantitative research focuses on describing a variety of experimental data employing the fragmentation function given by the parameterizations or model calculations. With the foundation of the transverse-momentum-dependent factorization, the QCD evolution of leading twist transverse-momentum-dependent fragmentation functions has also been established. In addition, the universality of fragmentation functions has been proven, albeit model-dependently, so that it is possible to perform a global analysis of experimental data in different high-energy reactions. The collective efforts may eventually reveal important information hidden in the shadow of nonperturbative physics. This review covers the following topics: transverse-momentum-dependent factorization and the corresponding QCD evolution, spin-dependent fragmentation functions at leading and higher twists, several experimental measurements and corresponding phenomenological studies, and some model calculations.

]]>Particles doi: 10.3390/particles6020028

Authors: Dim Idrisov Petr Parfenov Arkadiy Taranenko

The elliptic flow (v2) of produced particles is one of the important observables sensitive to the transport properties of the strongly interacting matter created in relativistic heavy-ion collisions. Detailed differential measurements of v2 are also foreseen in the future Multi-Purpose Detector (MPD) experiment at the Nuclotron based Ion Collider fAcility (NICA) at collision energies sNN = 4&ndash;11 GeV. Elliptic flow strongly depends on collision geometry, defined by the impact parameter b. Usually b is an input to theoretical calculations and can be deduced from experimental observables in the final state using the centrality procedure. In this work, we investigate the influence of the choice of centrality procedure on the elliptic flow measurements at NICA energies.

]]>Particles doi: 10.3390/particles6020027

Authors: Alexander Zinchenko Mikhail Kapishin Viktar Kireyeu Vadim Kolesnikov Alexander Mudrokh Dilyana Suvarieva Veronika Vasendina Dmitry Zinchenko

Study of the strangeness production in heavy-ion collisions is one of the most important parts of the physics program of the BM@N and MPD experiments at the NICA accelerator complex. With collision energies sNN of 2.3&ndash;3.3 GeV in the fixed target mode at BM@N and 4&ndash;11 GeV in the collider mode at MPD, the experiments will cover the region of the maximum net baryon density and provide high-statistics complementary data on different physics probes. In this paper, some results of Monte Carlo studies of hyperon production with the BM@N and MPD experiments are presented, demonstrating their performance for investigation of the objects with strangeness.

]]>Particles doi: 10.3390/particles6020026

Authors: Thomas Klähn Lee C. Loveridge Mateusz Cierniak

In this study, we discuss how iterative solutions of QCD-inspired gap-equations at the finite chemical potential demonstrate domains of chaotic behavior as well as non-chaotic domains, which represent one or the other of the only two&mdash;usually distinct&mdash;positive mass gap solutions with broken or restored chiral symmetry, respectively. In the iterative approach, gap solutions exist which exhibit restored chiral symmetry beyond a certain dynamical cut-off energy. A chirally broken, non-chaotic domain with no emergent mass poles and hence with no quasi-particle excitations exists below this energy cut-off. The transition domain between these two energy-separated domains is chaotic. As a result, the dispersion relation is that of quarks with restored chiral symmetry, cut at a dynamical energy scale, and determined by fractal structures. We argue that the chaotic origin of the infrared cut-off could hint at a chaotic nature of confinement and the deconfinement phase transition.

]]>Particles doi: 10.3390/particles6010025

Authors: Sergei B. Popov Maxim S. Pshirkov

Fast radio bursts (FRBs) were discovered only in 2007. However, the number of known events and sources of repeating bursts grows very rapidly. In the near future, the number of events will be &#8819;104 and the number of repeaters &#8819;100. Presently, there is a consensus that most of the sources of FRBs might be neutron stars (NSs) with large magnetic fields. These objects might have different origin as suggested by studies of their host galaxies which represent a very diverse sample: from regions of very active star formation to old globular clusters. Thus, in the following decade we expect to have a very large sample of events directly related to extragalactic magnetars of different origin. This might open new possibilities to probe various aspects of NS physics. In the review we briefly discuss the main directions of such future studies and summarize our present knowledge about FRBs and their sources.

]]>Particles doi: 10.3390/particles6010024

Authors: Marina Kozhevnikova Yuri B. Ivanov

Light-nuclei production in relativistic heavy-ion collisions is simulated within an updated Three-fluid Hydrodynamics-based Event Simulator Extended by UrQMD (Ultra-relativistic Quantum Molecular Dynamics) final State interactions (THESEUS). The simulations are performed in the collision energy range of sNN= 6.4&ndash;19.6 GeV. The light-nuclei are produced within the thermodynamical approach on an equal basis with hadrons. Since the light nuclei do not participate in the UrQMD evolution, the only additional parameter related to the light nuclei, i.e., the energy density of late freeze-out, is used for the imitation of the afterburner stage of the collision. The updated THESEUS provides a reasonable reproduction of data on bulk observables of the light nuclei, especially their functional dependence on the collision energy and light-nucleus mass. Various ratios, d/p, t/p, t/d, and N(t)&times;N(p)/N2(d), are also considered. Imperfect reproduction of the light-nuclei data leaves room for medium effects in produced light nuclei.

]]>Particles doi: 10.3390/particles6010023

Authors: Daniel S. Carman Ralf W. Gothe Victor I. Mokeev Craig D. Roberts

Understanding the strong interaction dynamics that govern the emergence of hadron mass (EHM) represents a challenging open problem in the Standard Model. In this paper we describe new opportunities for gaining insight into EHM from results on nucleon resonance (N*) electroexcitation amplitudes (i.e., &gamma;vpN* electrocouplings) in the mass range up to 1.8 GeV for virtual photon four-momentum squared (i.e., photon virtualities Q2) up to 7.5 GeV2 available from exclusive meson electroproduction data acquired during the 6-GeV era of experiments at Jefferson Laboratory (JLab). These results, combined with achievements in the use of continuum Schwinger function methods (CSMs), offer new opportunities for charting the momentum dependence of the dressed quark mass from results on the Q2-evolution of the &gamma;vpN* electrocouplings. This mass function is one of the three pillars of EHM and its behavior expresses influences of the other two, viz. the running gluon mass and momentum-dependent effective charge. A successful description of the &Delta;(1232)3/2+ and N(1440)1/2+ electrocouplings has been achieved using CSMs with, in both cases, common momentum-dependent mass functions for the dressed quarks, for the gluons, and the same momentum-dependent strong coupling. The properties of these functions have been inferred from nonperturbative studies of QCD and confirmed, e.g., in the description of nucleon and pion elastic electromagnetic form factors. Parameter-free CSM predictions for the electrocouplings of the &Delta;(1600)3/2+ became available in 2019. The experimental results obtained in the first half of 2022 have confirmed the CSM predictions. We also discuss prospects for these studies during the 12-GeV era at JLab using the CLAS12 detector, with experiments that are currently in progress, and canvass the physics motivation for continued studies in this area with a possible increase of the JLab electron beam energy up to 22 GeV. Such an upgrade would finally enable mapping of the dressed quark mass over the full range of distances (i.e., quark momenta) where the dominant part of hadron mass and N* structure emerge in the transition from the strongly coupled to perturbative QCD regimes.

]]>Particles doi: 10.3390/particles6010022

Authors: Alejandro Ayala Isabel Dominguez Ivonne Maldonado Maria Elena Tejeda-Yeomans

Due to its sensitivity to the dynamics of strongly interacting matter subject to extreme conditions, hyperon global polarization has become an important observable to study the system created in relativistic heavy-ion collisions. Recently, the STAR and HADES collaborations have measured the global polarization of both &Lambda; and &Lambda;&macr; produced in semi-central collisions in a wide range of collision energies. The polarization excitation functions show an increasing trend as the collision energy decreases, with the increase being more pronounced for the &Lambda;&macr;. In this work, we make a summary of a core-corona model that we have developed to quantify the global polarization contributions from &Lambda; and &Lambda;&macr; created in different regions of the fireball. The core-corona model assumes that &Lambda;s and &Lambda;&macr;s are produced in both regions, the high-density core and the lower density corona, with different relative abundances which modulate the polarization excitation function. We have shown that the model works well for the description of experimental results. The global polarization excitation functions computed with the model show a peak at different collision energies in the region sNN&le;10 GeV. Finally, we discuss and report on the model global polarization predictions for BES-II, NICA and CBM at FAIR and HADES energies.

]]>Particles doi: 10.3390/particles6010021

Authors: Viktar Kireyeu Vadim Kolesnikov Alexander Zinchenko Veronika Vasendina Alexander Mudrokh

The production of nuclei and hypernuclei is of interest for experimental and theoretical studies: it is a big question how such weakly bound objects survive in a hot, dense environment and which new insights on the heavy-ion collisions dynamics they can bring us. We present the results on the hypernuclei feasibility study for the flagship Nuclotron-based Ion Collider fAcility (NICA)/Multi-Purpose Detector (MPD) experiment at the Joint Institute for Nuclear Research (JINR) in Dubna using the Parton-Hadron-Quantum-Molecular Dynamics (PHQMD) transport approach and a realistic reconstruction chain.

]]>Particles doi: 10.3390/particles6010020

Authors: Hans Ströher Sebastian M. Schmidt Paolo Lenisa Jörg Pretz

Electric Dipole Moments (EDM) of particles (leptons, nucleons, and light nuclei) are currently deemed one of the best indicators for new physics, i.e., phenomena which lie outside the Standard Model (SM) of elementary particle physics&mdash;so-called physics &ldquo;Beyond-the-Standard-Model&rdquo; (BSM). Since EDMs of the SM are vanishingly small, a finite permanent EDM would indicate charge-parity (CP) symmetry violation in addition to the well-known sources of the SM, and could explain the baryon asymmetry of the Universe, while an oscillating EDM would hint at a possible Dark Matter (DM) field comprising axions or axion-like particles (ALPs). A new approach exploiting polarized charged particles (proton, deuteron, 3He) in precision storage rings offers the prospect to push current experimental EDM upper limits significantly further, including the possibility of an EDM discovery. In this paper, we describe the scientific background and the steps towards the realization of a precision storage ring, which will make such measurements possible.

]]>Particles doi: 10.3390/particles6010019

Authors: Nikita Tsegelnik Evgeni Kolomeitsev Vadym Voronyuk

The gold&ndash;gold collisions at sNN=7.7 and 11.5 GeV are simulated within the PHSD transport model. In each collision event, the spectator nucleons are separated and the fluidization procedure for the participants is performed. The local velocities are determined in the Landau frame and the kinematic and thermal vorticity fields are evaluated. We analyze the thermodynamic properties of the cells where &Lambda;s and &Lambda;&macr;s were born or had their last interaction. Such cells contribute to the formation of the observed global polarization of hyperons induced by the thermal vorticity of the medium. The &Lambda;&macr; polarization signal is found to be mainly determined by hot, dense, and highly vortical cells at the earlier stage of the collision, whereas the &Lambda; polarization signal is accumulated over the longer time and includes cells with lower vorticity. The calculated global polarizations for both &Lambda;s and &Lambda;&macr;s agree well with the experimental finding by the STAR collaboration at energy sNN=11.5&nbsp;GeV. For collisions at sNN=7.7&nbsp;GeV, we can reproduce the STAR data for &Lambda; hyperons, but significantly underpredict the observed global polarization of &Lambda;&macr;. Furthermore, we consider the centrality dependence of the hyperon polarization in collisions at 7.7 GeV. It increases with an increase of centrality, reaches a maximum at 65&ndash;75% and then starts decreasing rapidly for peripheral collisions.

]]>Particles doi: 10.3390/particles6010018

Authors: Mikhail Malaev Victor Riabov

ALICE-3 is being designed as a next-generation heavy-ion experiment to be operated at the high-luminosity Large Hadron Collider. With luminosities higher by a factor of fifty, ALICE-3 will be able to study5 properties of quark&ndash;gluon matter with probes and precision which were previously unavailable due to small cross sections, high background levels, and insufficient detector sensitivity. In particular, the properties of hot and dense QCD matter will be studied by measuring production cross sections, flow coefficients, azimuthal angular correlations and nuclear modification factors for open-charm hadrons. In this contribution, we present the results of feasibility studies for the measurement of ground and excited states of open-charm mesons in decay channels D0 &rarr; K&minus; + &pi;+ + &pi;0, D*(2007)0 &rarr; D0 + &gamma; and D*(2010)&plusmn; &rarr; D0 + &pi;&plusmn; in pp, p-Pb and Pb-Pb collisions at LHC energies using the ALICE-3 experimental setup. We formulate the main requirements for the selection of particles and their combinations to ensure reliable signal extraction in a wide transverse momentum range and estimate the minimum size of the required data samples. The results obtained are also compared to previous findings for the open-charm measurements in different decay channels.

]]>Particles doi: 10.3390/particles6010017

Authors: Mauricio Narciso Ferreira Joannis Papavassiliou

The dynamics of the QCD gauge sector give rise to non-perturbative phenomena that are crucial for the internal consistency of the theory; most notably, they account for the generation of a gluon mass through the action of the Schwinger mechanism, the taming of the Landau pole, the ensuing stabilization of the gauge coupling, and the infrared suppression of the three-gluon vertex. In the present work, we review some key advances in the ongoing investigation of this sector within the framework of the continuum Schwinger function methods, supplemented by results obtained from lattice simulations.

]]>Particles doi: 10.3390/particles6010016

Authors: Simone Bordoni Denis Stanev Tommaso Santantonio Stefano Giagu

We investigate the possibility to apply quantum machine learning techniques for data analysis, with particular regard to an interesting use-case in high-energy physics. We propose an anomaly detection algorithm based on a parametrized quantum circuit. This algorithm was trained on a classical computer and tested with simulations as well as on real quantum hardware. Tests on NISQ devices were performed with IBM quantum computers. For the execution on quantum hardware, specific hardware-driven adaptations were devised and implemented. The quantum anomaly detection algorithm was able to detect simple anomalies such as different characters in handwritten digits as well as more complex structures such as anomalous patterns in the particle detectors produced by the decay products of long-lived particles produced at a collider experiment. For the high-energy physics application, the performance was estimated in simulation only, as the quantum circuit was not simple enough to be executed on the available quantum hardware platform. This work demonstrates that it is possible to perform anomaly detection with quantum algorithms; however, as an amplitude encoding of classical data is required for the task, due to the noise level in the available quantum hardware platform, the current implementation cannot outperform classic anomaly detection algorithms based on deep neural networks.

]]>Particles doi: 10.3390/particles6010015

Authors: Cédric Mezrag

This paper review the modelling efforts regarding Generalised Parton Distributions (GPDs) using continuum techniques relying on Dyson&ndash;Schwinger and Bethe&ndash;Salpeter equations. The definition and main properties of the GPDs are first recalled. Then, we detail the strategies developed in the last decade in the meson sector, highlighting that observables connected to the pion GPDs may be measured at future colliders. We also highlight the challenges one will face when targeting baryons in the future.

]]>Particles doi: 10.3390/particles6010014

Authors: Yuri B. Ivanov Alexei A. Soldatov

We review recent studies of vortical motion and the resulting polarization of &Lambda; hyperons in heavy-ion collisions at NICA energies, in particular, within the model of three-fluid dynamics (3FD). This includes predictions of the global &Lambda; polarization and ring structures that appear in Au+Au collisions. The global &Lambda; polarization in Au+Au collisions is calculated, including its rapidity and centrality dependence. The contributions of the thermal vorticity and meson-field term (proposed by Csernai, Kapusta, and Welle) to the global polarization are considered. The results are compared with data from recent STAR and HADES experiments. It is predicted that the polarization maximum is reached at sNN&asymp; 3 GeV if the measurements are performed with the same acceptance. It is demonstrated that a pair of vortex rings are formed, one at forward rapidities and another at backward rapidities, in ultra-central Au+Au collisions at sNN&gt; 4 GeV. The vortex rings carry information about the early stage of the collision, in particular, the stopping of baryons. It is shown that these rings can be detected by measuring the ring observable R&Lambda;, even in the midrapidity region at sNN= 5&ndash;20 GeV. At forward/backward rapidities, the R&Lambda; signal is expected to be stronger. The possibility of observing the vortex-ring signal against the background of non-collective transverse polarization is discussed.

]]>Particles doi: 10.3390/particles6010013

Authors: Sergey Mikhailovich Troshin Nikolai Evgenjevich Tyurin

In this study, we consider the symmetry property of the inelastic overlap function and its relation to the reflective scattering mode appearance. This symmetry property disfavors an exclusion of one of the scattering modes&mdash;the reflective mode&mdash;when approaching the asymptotic limit. Predominance of the particular mode correlates with the energy and impact parameters ranges.

]]>Particles doi: 10.3390/particles6010012

Authors: Rico Zöllner Minghui Ding Burkhard Kämpfer

In this paper, the impact of core mass on the compact/neutron-star mass-radius relation is studied. Besides the mass, the core is parameterized by its radius and surface pressure, which supports the outside one-component Standard Model (SM) matter. The core may accommodate SM matter with unspecified (or poorly known) equation-of-state or several components, e.g., consisting of admixtures of Dark Matter and/or Mirror World matter etc. beyond the SM. Thus, the admissible range of masses and radii of compact stars can be considerably extended.

]]>Particles doi: 10.3390/particles6010011

Authors: Emanuel V. Chimanski Ronaldo V. Lobato Andre R. Goncalves Carlos A. Bertulani

The description of the stellar interior of compact stars remains as a big challenge for the nuclear astrophysics community. The consolidated knowledge is restricted to density regions around the saturation of hadronic matter &rho;0=2.8&times;1014gcm&minus;3, regimes where our nuclear models are successfully applied. As one moves towards higher densities and extreme conditions up to the quark/gluons deconfinement, little can be said about the microphysics of the equation of state (EoS). Here, we employ a Markov Chain Monte Carlo (MCMC) strategy to access the variability at high density regions of polytropic piecewise models for neutron star (NS) EoS or possible hybrid stars, i.e., a NS with a small quark-matter core. With a fixed description of the hadronic matter for low density, below the nuclear saturation density, we explore a variety of models for the high density regimes leading to stellar masses near to 2.5M&#8857;, in accordance with the observations of massive pulsars. The models are constrained, including the observation of the merger of neutrons stars from VIRGO-LIGO and with the pulsar observed by NICER. In addition, we also discuss the possibility of the use of a Bayesian power regression model with heteroscedastic error. The set of EoS from the Laser Interferometer Gravitational-Wave Observatory (LIGO) was used as input and treated as the data set for the testing case.

]]>Particles doi: 10.3390/particles6010010

Authors: Leif Holmlid

Laser-induced nuclear reactions in ultra-dense hydrogen H(0) (review in Physica Scripta 2019) create mesons (kaons and pions). These mesons decay mainly to muons. The muons created are useful (patented source) for the muon-induced fusion process. The sign of the muons from the source depends on the initial baryons used. With D(0) (ultra-dense deuterium) the source produces mainly positive muons and with p(0) (ultra-dense protium) the source produces mainly negative muons. Negative muons are required for muon-induced fusion. This charge asymmetry was reported earlier, and has now been confirmed by experiments with a coil current transformer as the beam detector. The current coil detector would give no signal from the muons if charge symmetry existed. The charge asymmetry could indicate unknown processes, for example, caused by the different annihilation processes in D(0) and p(0). The conclusions of a new analysis of the results are presented here. Using D(0) in the muon source, the asymmetry is likely due to the capture of &micro;- in D atoms and D2 molecules. This leads to emission of excess &micro;+ from D(0). With p(0) in the muon source, the capture rate of &micro;- is lower than in D(0). The emitted number of &micro;+ will be decreased by the reaction between &micro;+ and the surrounding abundant electrons, forming neutral muonium particles. This effect decreases the amount of emitted &micro;+ for both p(0) and D(0), and it is proposed to be the main reason for a larger fraction of emitted &micro;- in the case of p(0). Thus, there is no dominant emission of negative muons which would violate charge conservation.

]]>Particles doi: 10.3390/particles6010009

Authors: Dmitry Blau Dmitri Peresunko

Direct photons provide a possibility to test properties of hot matter created in proton&ndash;proton (pp), proton&ndash;nucleus (p&ndash;A) or nucleus&ndash;nucleus (A&ndash;A) collisions. As they are created in charged particles&rsquo; scatterings and freely escape the hot region, they provide a tool to test all stages of the collision: the scattering of the partons of incoming nucleons, pre-equilibrium evolution and collective expansion of hot quark&ndash;gluon matter created in nucleus&ndash;nucleus collisions. Comparing direct photon production in pp, p&ndash;A and A&ndash;A collisions, one can check the scaling with the number of binary collisions expected at a high transverse momentum range and obtain insight into the hot and cold hadronic matter properties with soft photons. The collective elliptic flow of direct photons is a unique possibility to trace the collective flow formation and space&ndash;time evolution of the fireball. We review the experimental results on direct photon production in pp, p&ndash;A and A&ndash;A collisions at the Super Proton Synchroton (SPS), the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC) energies and discuss an agreement of theoretical predictions with measurements. Finally, we present predictions of direct photon spectra and collective flow for lower energy collisions expected at the Nuclotron-based Ion Collider fAcility (NICA) and the Facility for Antiproton and Ion Research (FAIR).

]]>Particles doi: 10.3390/particles6010008

Authors: David Chester Alessio Marrani Michael Rios

Six-dimensional spinors with Spin(3,3) symmetry are utilized to efficiently encode three generations of matter. E8(&minus;24) is shown to contain physically relevant subgroups with representations for GUT groups, spacetime symmetries, three generations of the standard model fermions, and Higgs bosons. Pati&ndash;Salam, SU(5), and Spin(10) grand unified theories are found when a single generation is isolated. For spacetime symmetries, Spin(4,2) may be used for conformal symmetry, AdS5&rarr;dS4, or simply broken to Spin(3,1) of a Minkowski space. Another class of representations finds Spin(2,2) and can give AdS3 with various GUTs. An action for three generations of fermions in the Majorana&ndash;Weyl spinor 128 of Spin(4,12) is found with Spin(3) flavor symmetry inside E8(&minus;24). The 128 of Spin(12,4) can be regarded as the tangent space to a particular pseudo-Riemannian form of the octo-octonionic Rosenfeld projective plane E8(&minus;24)/Spin(12,4)=(OsxO)P2.

]]>Particles doi: 10.3390/particles6010007

Authors: Igor É. Bulyzhenkov

Maxwell&rsquo;s electrodynamics admits radial charge densities of the elementary organization with one vertex of the spherical symmetry. A multi-vertex distribution of sharply inhomogeneous charge densities can also be described by monistic field solutions to Maxwell&rsquo;s equations&ndash;equalities. Coulomb&ndash;Lorentz forces are exerted locally to correlated electric densities in their volume organization with the fixed self-energy integral. The long-range Coulomb interaction between the dense peaks of the charged space continuum can be described quantitatively through bulk integrals of local tensions within observable bodies in favor of the monistic all-unity in the material space physics of Descartes and Russian cosmists.

]]>Particles doi: 10.3390/particles6010006

Authors: Particles Editorial Office Particles Editorial Office

High-quality academic publishing is built on rigorous peer review [...]

]]>Particles doi: 10.3390/particles6010005

Authors: Ioannis Contopoulos Athanasios C. Tzemos Foivos Zanias George Contopoulos

This paper demonstrates how a classical detector that collects non-interacting individual classical massive free particles can generate a quantum interference pattern. The proposed classical picture requires that particles carry the information of a phase equal to an action integral along their trajectory. At the point of their detection, a special type of detector collects the phases from all individual particles reaching it, adds them up over time as complex numbers, and divides them by the square root of their number. The detector announces a number of detections equal to the square of the amplitude of the resulting complex number. An interference pattern is gradually built from the collection of particle phases in the detection bins of the detector after several repetitions of the experiment. We obtain perfect agreement with three solutions of the Schr&ouml;dinger equation for free particles: a Gaussian wavepacket, two Gaussian wavepackets approaching each other, and a Gaussian wavepacket reflecting off a wall. The main conclusion of the present work is that the interference of quantum mechanics is basically due to the detectors that collect the particles when there are macroscopic detectors operating as proposed. Finally, a simple physical experiment with a single-photon detector is proposed that will be able to test our theory.

]]>Particles doi: 10.3390/particles6010004

Authors: Minghui Ding Craig Roberts Sebastian Schmidt

Visible matter is characterised by a single mass scale; namely, the proton mass. The proton’s existence and structure are supposed to be described by quantum chromodynamics (QCD); yet, absent Higgs boson couplings, chromodynamics is scale-invariant. Thus, if the Standard Model is truly a part of the theory of Nature, then the proton mass is an emergent feature of QCD; and emergent hadron mass (EHM) must provide the basic link between theory and observation. Nonperturbative tools are necessary if such connections are to be made; and in this context, we sketch recent progress in the application of continuum Schwinger function methods to an array of related problems in hadron and particle physics. Special emphasis is given to the three pillars of EHM—namely, the running gluon mass, process-independent effective charge, and running quark mass; their role in stabilising QCD; and their measurable expressions in a diverse array of observables.

]]>Particles doi: 10.3390/particles6010003

Authors: James M. Lattimer

A review is made of constraints on the nuclear symmetry energy parameters arising from nuclear binding energy measurements, theoretical chiral effective field predictions of neutron matter properties, the unitary gas conjecture, and measurements of neutron skin thicknesses and dipole polarizabilities. While most studies have been confined to the parameters SV and L, the important roles played by, and constraints on Ksym, or, equivalently, the neutron matter incompressibility KN, are discussed. Strong correlations among SV,L, and KN are found from both nuclear binding energies and neutron matter theory. However, these correlations somewhat differ in the two cases, and those from neutron matter theory have smaller uncertainties. To 68% confidence, it is found from neutron matter theory that SV=32.0&plusmn;1.1 MeV, L=51.9&plusmn;7.9 MeV and KN=152.2&plusmn;38.1 MeV. Theoretical predictions for neutron skin thickness and dipole polarizability measurements of the neutron-rich nuclei 48Ca, 120Sn, and 208Pb are compared to recent experimental measurements, most notably the CREX and PREX neutron skin experiments from Jefferson Laboratory. By themselves, PREX I+II measurements of 208Pb and CREX measurement of 48Ca suggest L=121&plusmn;47 MeV and L=&minus;5&plusmn;40 MeV, respectively, to 68% confidence. However, we show that nuclear interactions optimally satisfying both measurements imply L=53&plusmn;13 MeV, nearly the range suggested by either nuclear mass measurements or neutron matter theory, and is also consistent with nuclear dipole polarizability measurements. This small parameter range implies R1.4=11.6&plusmn;1.0 km and &Lambda;1.4=228&minus;90+148, which are consistent with NICER X-ray and LIGO/Virgo gravitational wave observations of neutron stars.

]]>Particles doi: 10.3390/particles6010002

Authors: Vinh Ba Luong Dim Idrisov Petr Parfenov Arkadiy Taranenko

The elliptic flow v2 is one of the key observables sensitive to the transport properties of the strongly interacting matter formed in relativistic heavy-ion collisions. In this work, we report on the calculations of v2 and its fluctuations of charged hadrons produced in Au+Au collisions at center-of-mass energy per nucleon pair sNN = 7.7 and 11.5 GeV from several transport models and provide a direct comparison with published results from the STAR experiment. This study motivates further experimental investigations of v2 and its fluctuations with the Multi-Purpose Detector (MPD) at the NICA Collider.

]]>Particles doi: 10.3390/particles6010001

Authors: Giuseppe Nisticò

Dirac&rsquo;s theory is not the unique theory consistent with the physical principles specific of a free spin-one-half particle. In fact, we derive classes of theories of an elementary free particle from the principle of Poincar&eacute;&rsquo;s invariance and from the principle of the covariance of the position. The theory of Dirac is just one of these theories, characterized by singular predictions, namely, the zitterbewegung. Yet, the class here derived contains families of consistent theories without singular predictions. For the time being, the experimental verifiability of these alternative theories is restricted to the predictions of free-particle theories for ideal experiments.

]]>Particles doi: 10.3390/particles5040041

Authors: Thomas Settlemyre Hua Zheng Aldo Bonasera

In the collision of two heavy ions, the strong repulsion coming from the Coulomb field is enough to produce e+e&minus; pair(s) from vacuum fluctuations. The energy is provided by the kinetic energy of the ions and the Coulomb interaction at the production point. If, for instance, the electron is located at the center of mass (C.M.) of the two ions moving along the z-axis, and the positron is at a distance x from the electron, the ions can be accelerated towards each other since the Coulomb barrier is lowered by the presence of the electron. This screening results in an increase in the kinetic energy of the colliding ions and may result in an increase in the fusion probability of light ions above the adiabatic limit.

]]>Particles doi: 10.3390/particles5040040

Authors: Petr Parfenov

The anisotropic flow is one of the important observables sensitive to the equation of state (EOS) and transport properties of the strongly interacting matter created in relativistic heavy-ion collisions. In this work, we report a detailed multi-differential study of the directed (v1), elliptic (v2), triangular (v3), and quadrangular (v4) flow coefficients of protons in relativistic heavy-ion collisions at sNN = 2.2&ndash;4.5 GeV using several hadronic transport models. Recent published results for Au + Au collisions at sNN = 2.4 GeV from HADES experiment and at sNN = 3.0 GeV from the STAR experiment have been used for comparison. The study motivates further experimental investigations of the anisotropic collective flow of protons and neutrons in a high baryon density region.

]]>Particles doi: 10.3390/particles5040039

Authors: Nizami A. Abdulov Anatoly V. Kotikov Artem Lipatov

A new type of parametrization for parton distribution functions in the proton, based on their Q2-evolution at large and small x values, is constructed. In our analysis, the valence and nonsinglet parts obey the Gross&ndash;Llewellyn&ndash;Smith and Gottfried sum rules, respectively. For the singlet quark and gluon densities, momentum conservation is taken into account. Then, using the Kimber&ndash;Martin&ndash;Ryskin prescription, we extend the consideration to Transverse Momentum Dependent (TMD, or unintegrated) gluon and quark distributions in the proton, which currently plays an important role in a the number of phenomenological applications. The analytical expressions for the latter, valid for both low and large x, are derived for the first time.

]]>Particles doi: 10.3390/particles5040038

Authors: Oleksii Ivanytskyi David B. Blaschke

We generalize a recently proposed confining relativistic density-functional approach to the case of density-dependent vector and diquark couplings. The particular behavior of these couplings is motivated by the non-perturbative gluon exchange in dense quark matter and provides the conformal limit at asymptotically high densities. We demonstrate that this feature of the quark matter EoS is consistent with a significant stiffness in the density range typical for the interiors of neutron stars. In order to model these astrophysical objects, we construct a family of hybrid quark-hadron EoSs of cold stellar matter. We also confront our approach with the observational constraints on the mass&ndash;radius relation of neutron stars and their tidal deformabilities and argue in favor of a quark matter onset at masses below 1.0M&#8857;.

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Authors: Banibrata Mukhopadhyay Mukul Bhattacharya

Over the past several years, there has been enormous interest in massive neutron stars and white dwarfs due to either their direct or indirect evidence. The recent detection of gravitational wave event GW190814 has confirmed the existence of compact stars with masses as high as &sim;2.5&ndash;2.67 M&#8857; within the so-called mass gap, indicating the existence of highly massive neutron stars. One of the primary goals to invoke massive compact objects was to explain the recent detections of over a dozen Type Ia supernovae, whose peculiarity lies with their unusual light curve, in particular the high luminosity and low ejecta velocity. In a series of recent papers, our group has proposed that highly magnetised white dwarfs with super-Chandrasekhar masses can be promising candidates for the progenitors of these peculiar supernovae. The mass-radius relations of these magnetised stars are significantly different from those of their non-magnetised counterparts, which leads to a revised super-Chandrasekhar mass-limit. These compact stars have wider ranging implications, including those for soft gamma-ray repeaters, anomalous X-ray pulsars, white dwarf pulsars and gravitational radiation. Here we review the development of the subject over the last decade or so, describing the overall state of the art of the subject as it stands now. We mainly touch upon the possible formation channels of these intriguing stars as well as the effectiveness of direct detection methods. These magnetised stars can have many interesting consequences, including reconsideration of them as possible standard candles.

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Authors: Liberato De Caro

Electric charges and masses of elementary fermions of the Standard Model and fundamental physical constants (speed of light in vacuum, Planck constant, gravitational constant, vacuum permittivity, electron charge) are related through a simple equation. This new relation links 10 of the free parameters of the Standard Model&mdash;the masses of the three charged leptons and six quarks, and the electromagnetic coupling&mdash;in a compact formula, leaving strong constraints for allowing further elementary charged fermions beyond the Standard Model&rsquo;s physics. The formula is not derived by theoretical calculations, but it is based on the empirically measured values of the electric charges and proper masses of the known elementary fermions.

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Authors: Victor Henner Tatyana Belozerova

We compare two methods for obtaining the parameters of overlapping resonances. The convenience of the Breit&ndash;Wigner (BW) approach is based on the fact that it operates with the masses and widths of the states. For several resonances with the same quantum numbers, a sum of BW functions violates the unitarity of the S-matrix. However, unitarity can be maintained by introducing interference phases to a BW implementation of scattering matrix formalism. A background can be added to the BW amplitudes in the standard way by using background phases. The K-matrix method is often used to analyze data related to several resonances with the same quantum numbers. It guarantees the unitarity of the S-matrix, but its parameters can be considered as resonance masses and widths only for well-spaced states. It also does not allow the separation of the resonant and background contributions in scattering amplitudes, which is critically important for determining parameters of wide resonances. To demonstrate the features of these methods, we consider several examples using simulated data.

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Authors: Igor A. Shovkovy

The validity of conventional Ohm&rsquo;s law is tested in the context of a rapidly evolving quark&ndash;gluon plasma produced in heavy-ion collisions. Here, we discuss the electromagnetic response using an analytical solution in kinetic theory. As conjectured previously, after switching on an electric field in a nonexpanding plasma, the time-dependent current is given by J(t)=(1&minus;e&minus;t/&tau;0)&sigma;0E, where &tau;0 is the transport relaxation time and &sigma;0 is the steady-state electrical conductivity. Such an incomplete electromagnetic response reduces the efficiency of the magnetic flux trapping in the quark&ndash;gluon plasma, and may prevent the observation of the chiral magnetic effect. Here, we extend the study to the case of a rapidly expanding plasma. We find that the decreasing temperature and the increasing transport relaxation time have opposite effects on the electromagnetic response. While the former suppresses the time-dependent conductivity, the latter enhances it.

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Authors: Alessandro Pesci

Starting from some results regarding the form of the Ricci scalar at a point P in a (particle-like) spacetime endowed with a minimum distance, we investigate how they might be accommodated, specifically for the case of null separations, in a as-simple-as-possible quantum structure for spacetime at P, and we try to accomplish this in terms of potentially operationally defined concepts. In so doing, we provide a possible explicit form for the operator expressing the Ricci scalar as a quantum observable, and give quantum-informational support, thus regardless of or before field equations, to associating with a patch of horizon an entropy proportional to its area.

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