*Particles*

**2024**,

*7*(2), 489-501; https://0-doi-org.brum.beds.ac.uk/10.3390/particles7020028 - 13 Jun 2024

**Abstract**

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Open AccessArticle

Probing the Dark Matter Capture Rate in a Local Population of Brown Dwarfs with IceCube Gen 2
by
**Pooja Bhattacharjee** and **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,
[...] Read more.

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 $\chi \chi \to \nu \overline{\nu}\nu \overline{\nu}$ 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 ${10}^{-36}\phantom{\rule{3.33333pt}{0ex}}{\mathrm{cm}}^{2}$ .
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(This article belongs to the Special Issue Selected Papers from “Dark Matter and Stars: Multi-Messenger Probes of Dark Matter and Modified Gravity”)

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Open AccessArticle

A Multiple Scattering-Based Technique for Isotopic Identification in Cosmic Rays
by
**Francesco Dimiccoli** and **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
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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.
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(This article belongs to the Special Issue Innovative Techniques for Particle Physics in Space)

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Open AccessArticle

Quantum Gravity Effective Action Provides Entropy of the Universe
by
**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
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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.
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(This article belongs to the Special Issue Feature Papers for *Particles* 2023)

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Open AccessArticle

Scales and Hierarchies: Planckian Signature in Standard Model
by
**Davide Fiscaletti** and **Ignazio Licata**

A model of a physical vacuum defined by a Gross–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
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A model of a physical vacuum defined by a Gross–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.
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(This article belongs to the Special Issue Feature Papers for *Particles* 2023)

Open AccessReview

Feature Selection Techniques for CR Isotope Identification with the AMS-02 Experiment in Space
by
**Marta Borchiellini**, **Leandro Mano**, **Fernando Barão** and **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
[...] Read more.

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’ 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’ 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’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.
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(This article belongs to the Special Issue Feature Papers for *Particles* 2023)

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Open AccessCorrection

Correction: Teslyk et al. Unruh Effect and Information Entropy Approach.
by
**Maksym Teslyk**, **Larissa Bravina** and **Evgeny Zabrodin**

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

Renormalisable Non-Local Quark–Gluon Interaction: Mass Gap, Chiral Symmetry Breaking and Scale Invariance
by
**Arpan Chatterjee**, **Marco Frasca**, **Anish Ghoshal** and **Stefan Groote**

We derive a Nambu–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
[...] Read more.

We derive a Nambu–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–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–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–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–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.
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Open AccessArticle

Characterization of RF System for MIR/THz Free Electron Lasers at Chiang Mai University
by
**Pitchayapak Kitisri**, **Jatuporn Saisut** and **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
[...] Read more.

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.
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(This article belongs to the Special Issue Generation and Application of High-Power Radiation Sources)

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Open AccessReview

Hadronic Light-by-Light Corrections to the Muon Anomalous Magnetic Moment
by
**Daniel Melo**, **Edilson Reyes** and **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
[...] Read more.

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 $g-2$ . 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–Barnes integrals. By our technique, the completeness of such kinematic singularity/zero-free tensor decomposition of the HLbL amplitude is explicitly checked.
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(This article belongs to the Special Issue Feature Papers for *Particles* 2023)

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Open AccessReview

Review on Minimally Extended Varying Speed of Light Model
by
**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
[...] Read more.

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.
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(This article belongs to the Special Issue Feature Papers for *Particles* 2023)

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Open AccessArticle

Can Black Holes or Other Relativistic Space Objects Be a Source of Dark Energy?
by
**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
[...] Read more.

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.
Full article

(This article belongs to the Special Issue Feature Papers for *Particles* 2023)

Open AccessArticle

Cosmological Mass of the Photon Related to Stueckelberg and Higgs Mechanisms
by
**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–de
[...] Read more.

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–de Sitter cosmological constant and horizon. This yields qualitative connections between microscopic ranges acquired by ${W}^{\pm}$ or ${Z}^{0}$ gauge Bosons and the cosmological scale and minimal mass acquired by *g*-photons. I apply this procedure to an established Stueckelberg–Higgs mechanism, while I consider a similar procedure for a pair of Higgs fields that may spontaneously break all U(1) × 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.
Full article

(This article belongs to the Special Issue Feature Papers for *Particles* 2023)

Open AccessArticle

Z Boson Emission by a Neutrino in de Sitter Expanding Universe
by
**Mihaela-Andreea Băloi**, **Cosmin Crucean** and **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,
[...] Read more.

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.
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(This article belongs to the Special Issue Feature Papers for *Particles* 2023)

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Open AccessArticle

Quantum Limit for the Emittance of Dirac Particles Carrying Orbital Angular Momentum
by
**Alessandro Curcio**, **Alessandro Cianchi** and **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
[...] Read more.

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–space area of Dirac particles carrying OAM. The results dramatically differ from the classical evaluation of phase–space areas, that would foresee no increase in emittance for beams in a coherent state of OAM. We discuss the quantization of the phase–space cell’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–space area occupied by the beam deviates from its quantum limit.
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(This article belongs to the Special Issue Feature Papers for *Particles* 2023)

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Open AccessArticle

New Aspect of Chiral
by
**Chuan-Xin Cui**, **Jin-Yang Li**, **Shinya Matsuzaki**, **Mamiya Kawaguchi** and **Akio Tomiya**

The violation of the $U\left(1\right)$ axial symmetry in QCD is stricter than the chiral $SU\left(2\right)$ breaking simply because of the presence of the quantum axial anomaly. If the QCD gauge coupling is sent to zero (the
[...] Read more.

The violation of the $U\left(1\right)$ axial symmetry in QCD is stricter than the chiral $SU\left(2\right)$ 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 $U\left(1\right)$ axial anomaly does not exist), the strength of the $U\left(1\right)$ axial breaking coincides with that of the chiral $SU\left(2\right)$ breaking, which we, in short, call an axial–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–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 $({m}_{l}\ne 0)$ and the massless strange quark (${m}_{s}=0$ ) due to the flavor-singlet nature of the topological susceptibility. This coincidence is robust and tied to the anomalous chiral Ward–Takahashi identity, which is operative even at hot QCD. This implies that the chiral $SU\left(2\right)$ symmetry is restored simultaneously with the $U\left(1\right)$ axial symmetry at high temperatures. This simultaneous restoration is independent of ${m}_{l}(\ne 0)$ 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–axial coincidence limit by working on a Nambu–Jona–Lasinio model with the $U\left(1\right)$ axial anomaly contribution properly incorporated. It is shown that, at high temperatures, the large differences between the restorations of the chiral $SU\left(2\right)$ symmetry and the $U\left(1\right)$ 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 $SU\left(2\right)$ and $U\left(1\right)$ axial breaking in QCD.
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(This article belongs to the Collection High Energy Physics)

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Open AccessCommunication

Experimental Study of Cold Dense Nuclear Matter
by
**Maria Patsyuk**, **Timur Atovullaev**, **Goran Johansson**, **Dmitriy Klimanskiy**, **Vasilisa Lenivenko**, **Sergey Nepochatykh** and **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
[...] Read more.

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.
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(This article belongs to the Special Issue Infinite and Finite Nuclear Matter (INFINUM))

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Open AccessArticle

Surface Vibrations of Bubble-like Superheavy Nuclei
by
**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
[...] Read more.

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.
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(This article belongs to the Special Issue Feature Papers for *Particles* 2023)

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Open AccessArticle

Exploring the Distribution and Impact of Bosonic Dark Matter in Neutron Stars
by
**Davood Rafiei Karkevandi**, **Mahboubeh Shahrbaf**, **Soroush Shakeri** and **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
[...] Read more.

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 ${m}_{\chi}\gtrsim 200$ MeV and $\lambda \lesssim 2\pi $ , DM-admixed NSs with $4\%\lesssim {F}_{\chi}\lesssim 20\%$ are consistent with the maximum mass and tidal deformability constraints.
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(This article belongs to the Special Issue Selected Papers from “Dark Matter and Stars: Multi-Messenger Probes of Dark Matter and Modified Gravity”)

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The Impact of Asymmetric Dark Matter on the Thermal Evolution of Nucleonic and Hyperonic Compact Stars
by
**Edoardo Giangrandi**, **Afonso Ávila**, **Violetta Sagun**, **Oleksii Ivanytskyi** and **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
[...] Read more.

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’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’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.
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Open AccessArticle

A New Look at
by
**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 $\mathrm{SU}{\left(3\right)}_{C}\times \mathrm{SU}{\left(3\right)}_{L}\times \mathrm{U}{\left(1\right)}_{X}$ ,
[...] Read more.

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 $\mathrm{SU}{\left(3\right)}_{C}\times \mathrm{SU}{\left(3\right)}_{L}\times \mathrm{U}{\left(1\right)}_{X}$ , 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*, ${B}_{d}$ and ${B}_{s}$ 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 $\beta =\pm k/\sqrt{3}$ , with $k=1,2$ . The results are used to determine the impact of 331 models on $b\to s$ processes and on the correlations among them, in the light of new experimental data recently released.
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(This article belongs to the Special Issue Feature Papers for *Particles* 2023)

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Special Issue in
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Feature Papers for Deadline: 20 June 2024

Special Issue in
Particles

Selected Papers from “Physics beyond the Standard Model in Leptonic & Hadronic Processes and Relevant Computing Tools”
Guest Editors: Alessandro Spatafora, Theocharis Kosmas, Mario E. Gómez, Odysseas KosmasDeadline: 30 June 2024

Special Issue in
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Testing Fundamental QED and BSM Physics Theories in Leptonic and Hadronic Processes
Guest Editors: Theocharis Kosmas, Hiroyasu Ejiri, John VergadosDeadline: 31 July 2024

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Collection Editor: Alexandru Jipa
Topical Collection in
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Collection Editors: Valery E. Lyubovitskij, Dmitry V. Kirpichnikov, Alexey S. Zhevlakov
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