Particles

13 pages, 755 KiB

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

Particles 2024, 7(2), 489-501; https://doi.org/10.3390/particles7020028 - 13 Jun 2024

Cited by 3 | Viewed by 621

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

χ χ \to ν \bar{ν} ν \bar{ν}

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} {cm}^{2}

. Full article

(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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12 pages, 885 KiB

Open AccessArticle

A Multiple Scattering-Based Technique for Isotopic Identification in Cosmic Rays

by Francesco Dimiccoli and Francesco Maria Follega

Particles 2024, 7(2), 477-488; https://doi.org/10.3390/particles7020027 - 2 May 2024

Viewed by 1392

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Innovative Techniques for Particle Physics in Space)

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12 pages, 504 KiB

Open AccessArticle

Quantum Gravity Effective Action Provides Entropy of the Universe

by Ken-ji Hamada

Particles 2024, 7(2), 465-476; https://doi.org/10.3390/particles7020026 - 2 May 2024

Viewed by 1453

Abstract

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 [...] Read more.

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. Full article

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

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30 pages, 400 KiB

Open AccessArticle

Scales and Hierarchies: Planckian Signature in Standard Model

by Davide Fiscaletti and Ignazio Licata

Particles 2024, 7(2), 435-464; https://doi.org/10.3390/particles7020025 - 22 Apr 2024

Viewed by 1369

Abstract

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 [...] Read more.

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. Full article

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

18 pages, 1376 KiB

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

Particles 2024, 7(2), 417-434; https://doi.org/10.3390/particles7020024 - 20 Apr 2024

Viewed by 1092

Abstract

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. Full article

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

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1 pages, 134 KiB

Open AccessCorrection

Correction: Teslyk et al. Unruh Effect and Information Entropy Approach. Particles 2022, 5, 157–170

by Maksym Teslyk, Larissa Bravina and Evgeny Zabrodin

Particles 2024, 7(2), 416; https://doi.org/10.3390/particles7020023 - 18 Apr 2024

Viewed by 696

Abstract

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

24 pages, 446 KiB

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

Particles 2024, 7(2), 392-415; https://doi.org/10.3390/particles7020022 - 12 Apr 2024

Cited by 3 | Viewed by 1549

Abstract

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. Full article

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10 pages, 897 KiB

Open AccessArticle

Characterization of RF System for MIR/THz Free Electron Lasers at Chiang Mai University

by Pitchayapak Kitisri, Jatuporn Saisut and Sakhorn Rimjaem

Particles 2024, 7(2), 382-391; https://doi.org/10.3390/particles7020021 - 11 Apr 2024

Viewed by 1380

Abstract

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. Full article

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

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55 pages, 652 KiB

Open AccessReview

Hadronic Light-by-Light Corrections to the Muon Anomalous Magnetic Moment

by Daniel Melo, Edilson Reyes and Raffaele Fazio

Particles 2024, 7(2), 327-381; https://doi.org/10.3390/particles7020020 - 10 Apr 2024

Cited by 1 | Viewed by 1310

Abstract

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. Full article

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

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18 pages, 348 KiB

Open AccessReview

Review on Minimally Extended Varying Speed of Light Model

by Seokcheon Lee

Particles 2024, 7(2), 309-326; https://doi.org/10.3390/particles7020019 - 9 Apr 2024

Cited by 4 | Viewed by 1837

Abstract

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. Full article

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

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12 pages, 264 KiB

Open AccessArticle

Can Black Holes or Other Relativistic Space Objects Be a Source of Dark Energy?

by Serge Parnovsky

Particles 2024, 7(2), 297-308; https://doi.org/10.3390/particles7020018 - 29 Mar 2024

Viewed by 1070

Abstract

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)

8 pages, 241 KiB

Open AccessArticle

Cosmological Mass of the Photon Related to Stueckelberg and Higgs Mechanisms

by Lorenzo Gallerani Resca

Particles 2024, 7(2), 289-296; https://doi.org/10.3390/particles7020017 - 29 Mar 2024

Viewed by 1433

Abstract

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)

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