Particles

14 pages, 543 KB

Open AccessArticle

Clusters of PBHs in a Framework of Multidimensional f(R)-Gravity

by Maxim Krasnov and Valery Nikulin

Particles 2026, 9(1), 12; https://doi.org/10.3390/particles9010012 - 3 Feb 2026

We investigate primordial black hole (PBH) production via the collapse of supercritical domain walls in a quadratic

f (R)

-gravity model with tensor extensions. The effective field theory for an extra space’s scalar curvature provides a foundation for the formation of [...] Read more.

We investigate primordial black hole (PBH) production via the collapse of supercritical domain walls in a quadratic

f (R)

-gravity model with tensor extensions. The effective field theory for an extra space’s scalar curvature provides a foundation for the formation of these dense walls. In our work, domain walls are found to be supercritical. Their properties were extensively studied in the literature, where it was demonstrated that they create wormholes and escape into baby universes through them. Closure of the wormhole leads to black hole creation, providing a mechanism for the production of primordial black holes in our model. We calculate the mass spectrum of such black holes and mass distribution within clusters of them. When accretion is accounted for, the black holes produced under this mechanism present viable dark matter candidates. Full article

(This article belongs to the Special Issue Selected Papers from XXVIII Workshop “What Comes Beyond the Standard Models?”: New Trends in Particle Cosmology)

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28 pages, 438 KB

Open AccessArticle

H

olographic

N

aturalness and Information See-Saw Mechanism for Neutrinos

by Andrea Addazi and Giuseppe Meluccio

Particles 2026, 9(1), 11; https://doi.org/10.3390/particles9010011 - 2 Feb 2026

Abstract

The microscopic origin of the de Sitter entropy remains a central puzzle in quantum gravity that is related to the cosmological constant problem. Within the paradigm of

H

olographic

N

aturalness, we propose that this entropy is carried by a vast number of [...] Read more.

The microscopic origin of the de Sitter entropy remains a central puzzle in quantum gravity that is related to the cosmological constant problem. Within the paradigm of

H

olographic

N

aturalness, we propose that this entropy is carried by a vast number of light, coherent degrees of freedom—called “hairons”—which emerge as the moduli of gravitational instantons on orbifolds. Starting from the Euclidean de Sitter instanton (

S^{4}

), we construct a new class of orbifold gravitational instantons,

S^{4} / Z_{N}

, where N corresponds to the de Sitter entropy. We demonstrate that the dimension of the moduli space of these instantons scales linearly with N, and we identify these moduli with the hairon fields. A

Z_{N}

symmetry, derived from Wilson loops in the instanton background, ensures the distinguishability of these modes, leading to the correct entropy count. The hairons acquire a mass of the order of the Hubble scale and exhibit negligible mutual interactions, suggesting that the de Sitter vacuum is a coherent state, or Bose–Einstein condensate, of these fundamental excitations. Then, we present a novel framework which unifies neutrino mass generation with the cosmological constant through gravitational topology and holography. The small neutrino mass scale emerges naturally from first principles, without requiring new physics beyond the Standard Model and Gravity. The gravitational Chern–Simons structure and its anomaly with neutrinos force a topological Higgs mechanism, leading to neutrino condensation via

S^{4} / Z_{N}

gravitational instantons. The number of topological degrees of freedom

N \sim M_{P}^{2} / Λ \sim 10^{120}

provides both the holographic counting of the de Sitter entropy and a

1 / N

information see-saw mechanism for neutrino masses. Our framework makes the following predictions: (i) a neutrino superfluid condensation forming Cooper pairs below meV energies, as a viable candidate for cold dark matter; (ii) a possible resolution of the strong CP problem through a QCD composite axion state; (iii) time-varying neutrino masses which track the evolution of dark energy; and (iv) several distinctive signatures in astroparticle physics, ultra-high-energy cosmic rays and high magnetic field experiments. Full article

(This article belongs to the Special Issue Selected Papers from XXVIII Workshop “What Comes Beyond the Standard Models?”: New Trends in Particle Cosmology)

8 pages, 1153 KB

Open AccessArticle

Evaluation of a Timepix3 Telescope for Applications as a Compton Scatter Polarimeter for Hard X- and Soft γ-Rays

by Jindrich Jelinek, Benedikt Bergmann and Petr Smolyanskiy

Particles 2026, 9(1), 10; https://doi.org/10.3390/particles9010010 - 2 Feb 2026

Abstract

This work presents a simulation study of a Timepix3 telescope composed of nine detectors for use as a Compton scatter polarimeter in the energy range of 35–100 keV. Four detectors carry 1 mm thick silicon (Si) sensors and five detectors carry 1 mm [...] Read more.

This work presents a simulation study of a Timepix3 telescope composed of nine detectors for use as a Compton scatter polarimeter in the energy range of 35–100 keV. Four detectors carry 1 mm thick silicon (Si) sensors and five detectors carry 1 mm thick cadmium telluride (CdTe) sensors. The modulation factor for 100% linearly polarized X-ray beams was found to be

μ_{100} > 70 %

in the energy range of 55–80 keV. The quality factor of the polarimeter has its maximum 12.8% at the energy 75 keV. The comparison of quality factors and the calculations of a hypothetical observation of the Crab nebula show that this multilayer Timepix3 approach is competitive with contemporary X-ray polarimeters. Full article

(This article belongs to the Special Issue Advances in Space AstroParticle Physics: Frontier Technologies for Particle Measurements in Space, 2025 Edition)

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14 pages, 4073 KB

Open AccessConference Report

High-Precision Cross-Sections for Galactic Cosmic Rays: Highlights from XSCRC2024 and Follow-Up Actions

by David Maurin, Fiorenza Donato and Saverio Mariani

Particles 2026, 9(1), 9; https://doi.org/10.3390/particles9010009 - 26 Jan 2026

Abstract

The interpretation of high-precision Galactic cosmic-ray data from AMS-02, CALET, DAMPE, etc., is fundamentally limited by nuclear cross-sections uncertainties. This proceeding highlights the results presented at the XSCRC2024 workshop, which aims at bringing together the cosmic-ray, nuclear, and particle physics communities, with the [...] Read more.

The interpretation of high-precision Galactic cosmic-ray data from AMS-02, CALET, DAMPE, etc., is fundamentally limited by nuclear cross-sections uncertainties. This proceeding highlights the results presented at the XSCRC2024 workshop, which aims at bringing together the cosmic-ray, nuclear, and particle physics communities, with the goal of improving cross-section measurements across various domains, from nuclei production for constraining cosmic-ray transport parameters, to antiproton and anti-deuteron production for dark matter searches. This workshop lead to a comprehensive roadmap for new cross-section measurements in the next decade, as well as other outcomes. Full article

(This article belongs to the Special Issue Advances in Space AstroParticle Physics: Frontier Technologies for Particle Measurements in Space, 2025 Edition)

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16 pages, 685 KB

Open AccessArticle

Identified-Hadron Spectra in π⁺ + Be at 60 GeV/c with Channel-Wise Subcollision Acceptance in PYTHIA 8 Angantyr

by Nuha Felemban

Particles 2026, 9(1), 8; https://doi.org/10.3390/particles9010008 - 19 Jan 2026

Abstract

Identified-hadron production (p,

π^{\pm}

,

K^{\pm}

) in

π^{+} + Be

at

p_{lab} = 60 GeV / c

(

\sqrt{s} ≃ 10.6 GeV

) is investigated using Pythia 8.315 (Monash tune) with the Angantyr extension. Differential multiplicities [...] Read more.

Identified-hadron production (p,

π^{\pm}

,

K^{\pm}

) in

π^{+} + Be

at

p_{lab} = 60 GeV / c

(

\sqrt{s} ≃ 10.6 GeV

) is investigated using Pythia 8.315 (Monash tune) with the Angantyr extension. Differential multiplicities

d^{2} n / (d p d θ)

are confronted with NA61/SHINE measurements across standard

θ

bins. Within the fluctuating-radii Double-Strikman (DS) scheme, two unsuppressed opacity mappings are compared to quantify systematics. In addition, a minimal extension is introduced: a flat, post-classification, channel-wise acceptance applied after ND/SD/DD/EL tagging. It acts on primary and secondary

π N

pairs, keeps hadronization fixed (Lund string), and leaves the internal event generation of each admitted subcollision unchanged. Opacity-mapping variations alone induce only percent-level differences and do not resolve the soft/forward tensions. By contrast, the flat acceptance—interpretable as a reduced effective ND weight—improves agreement across species and angles. It hardens the forward

π^{+}

spectra and lowers large-

θ

yields, produces milder charge-asymmetric changes for

π^{-}

consistent with the weaker leading feed, suppresses proton yields at all angles (with a residual

\sim 30 %

forward high-p deficit), and improves

K^{\pm}

, with a stronger effect for

K^{+}

than

K^{-}

. These results show that a geometry-blind reweighting of the subcollision mixture suffices to capture the main NA61/SHINE trends for

π^{+} + Be

at SPS energies without modifying hadronization. The approach provides a controlled baseline for subsequent, channel-balanced refinements and broader

π^{+} A

tuning. Full article

(This article belongs to the Section Nuclear and Hadronic Theory)

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11 pages, 4363 KB

Open AccessArticle

Testing and Characterization of Detection Plane Elements of the XGIS Instrument on Board the THESEUS Mission

by Smiriti Srivastava, Evgeny Demenev, Claudio Labanti, Lorenzo Amati, Riccardo Campana, Giuseppe Baldazzi, Edoardo Borciani, Paolo Calabretto, Francesco Ficorella, Ezequiel J. Marchesini, Giulia Mattioli, Ajay Sharma, David Novel, Giancarlo Pepponi and Enrico Virgilli

Particles 2026, 9(1), 7; https://doi.org/10.3390/particles9010007 - 18 Jan 2026

Abstract

This paper presents the procedures employed for experimental functional and performance characterization of a 2 × 2 pixel prototype detection system tailored specifically for the X and Gamma-ray Imaging Spectrometer (XGIS) instrument onboard the THESEUS mission. The XGIS system comprises of two coded [...] Read more.

This paper presents the procedures employed for experimental functional and performance characterization of a 2 × 2 pixel prototype detection system tailored specifically for the X and Gamma-ray Imaging Spectrometer (XGIS) instrument onboard the THESEUS mission. The XGIS system comprises of two coded masked wide field cameras integrated with monolithic SDDs (Silicon Drift Detectors) and CsI:Tl (Thallium doped-Cesium Iodide) scintillators, contributing to its broad X and

γ

-ray detection range. Given the space instrumentation complexity, thorough requirement qualification and testing procedures are essential. This work focuses on working principle, the testing setup utilized, and observed performance for the small scale four-pixel XGIS prototype. Furthermore, the alignment of light output performance of the four-pixel SDD and scintillator prototype detection system with the XGIS instrument requirements is emphasized. Full article

(This article belongs to the Special Issue Advances in Space AstroParticle Physics: Frontier Technologies for Particle Measurements in Space, 2025 Edition)

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22 pages, 26643 KB

Open AccessArticle

Critical Aspects in the Modeling of Sub-GeV Calorimetric Particle Detectors: The Case Study of the High-Energy Particle Detector (HEPD-02) on Board the CSES-02 Satellite

by Simona Bartocci, Roberto Battiston, Stefania Beolè, Franco Benotto, Piero Cipollone, Silvia Coli, Andrea Contin, Marco Cristoforetti, Cinzia De Donato, Cristian De Santis, Andrea Di Luca, Floarea Dumitrache, Francesco Maria Follega, Simone Garrafa Botta, Giuseppe Gebbia, Roberto Iuppa, Alessandro Lega, Mauro Lolli, Giuseppe Masciantonio, Matteo Mergè, Marco Mese, Riccardo Nicolaidis, Francesco Nozzoli, Alberto Oliva, Giuseppe Osteria, Francesco Palma, Federico Palmonari, Beatrice Panico, Stefania Perciballi, Francesco Perfetto, Piergiorgio Picozza, Michele Pozzato, Marco Ricci, Ester Ricci, Sergio Bruno Ricciarini, Zouleikha Sahnoun, Umberto Savino, Valentina Scotti, Enrico Serra, Alessandro Sotgiu, Roberta Sparvoli, Pietro Ubertini, Veronica Vilona, Simona Zoffoli and Paolo Zuccon Show full author list Hide full author list

Particles 2026, 9(1), 6; https://doi.org/10.3390/particles9010006 - 15 Jan 2026

Abstract

The accurate simulation of sub-GeV particle detectors is essential for interpreting experimental data and optimizing detector design. This work identifies and addresses several critical aspects in modeling such detectors, taking as a case study the High-Energy Particle Detector (HEPD-02), a space-borne instrument developed [...] Read more.

The accurate simulation of sub-GeV particle detectors is essential for interpreting experimental data and optimizing detector design. This work identifies and addresses several critical aspects in modeling such detectors, taking as a case study the High-Energy Particle Detector (HEPD-02), a space-borne instrument developed within the CSES-02 mission to measure electrons in the ∼3–100 MeV range, protons and light nuclei in the ∼30–200 MeV/n. The HEPD-02 instrument consists of a silicon tracker, plastic and LYSO scintillator calorimeters, and anticoincidence systems, making it a representative example of a complex low-energy particle detector operating in Low Earth Orbit. Key challenges arise from replicating intricate detector geometries derived from CAD models, selecting appropriate hadronic physics lists for low-energy interactions, and accurately describing the detector response—particularly quenching effects in scintillators and digitization in solid-state tracking planes. Particular attention is given to three critical aspects: the precise CAD-level geometry implementation, the impact of hadronic physics models on the detector response, and the parameterization of scintillation quenching. In this study, we present original solutions to these challenges and provide data–MC comparisons using data from HEPD-02 beam tests. Full article

(This article belongs to the Section Experimental Physics and Instrumentation)

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14 pages, 423 KB

Open AccessArticle

Coherent State Description of Astrophysical Gamma-Ray Amplification from a Para-Positronium Condensate

by Diego Julio Cirilo-Lombardo

Particles 2026, 9(1), 5; https://doi.org/10.3390/particles9010005 - 14 Jan 2026

Abstract

The para-positronium system

({}^{1}S_{0} P s)

is described by means of specially constructed coherent states (CSs) in the Klauder–Perelomov sense. It is analyzed from the physical point of view and from the geometry underlying the relevant symmetry group establishing the dynamics [...] Read more.

The para-positronium system

({}^{1}S_{0} P s)

is described by means of specially constructed coherent states (CSs) in the Klauder–Perelomov sense. It is analyzed from the physical point of view and from the geometry underlying the relevant symmetry group establishing the dynamics of the processes. In this new theoretical context, the possibility of a gamma-ray laser emission is investigated within a QFT context, showing explicitly that, in addition to the oscillator solution based only on a Bogoliubov approximation for the condensate, there is a second phase or “squeezed” stage by which physical features beyond the classical ones appear. Explicitly, while the generated photons are in the active medium (e.g., Ps-BEC), the evolution is described by a Heisenberg–Weyl coherent state with displacement operators dependent on the interaction time, which is related to the condensate shape. After the interaction time has elapsed, we explicitly demonstrate that the displacement operator of the

{}^{1}S_{0} P s

is transformed into a squeezed operator of the photonic fields modulated by the matrix element of the Positronium decay

M_{{}^{1}S_{0} P s} \to 2 γ

. We also show that this squeezed operator (belonging to the Metaplectic group) generates a non-classical radiation state spanning only even (s = 1/4) levels in the number of photons. The implications in astrophysical systems of interest, considering gamma-ray coherent emission and the possibility of an

{}^{1}S_{0} P s - B E C

in the context of pulsars, blazars, and quasars, are briefly discussed. Full article

(This article belongs to the Section Astroparticle Physics and Cosmology)

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17 pages, 3794 KB

Open AccessArticle

Spectral Performance of Single-Channel Plastic and GAGG Scintillator Bars of the CUbesat Solar Polarimeter (CUSP)

by Nicolas De Angelis, Abhay Kumar, Sergio Fabiani, Ettore Del Monte, Enrico Costa, Giovanni Lombardi, Alda Rubini, Paolo Soffitta, Andrea Alimenti, Riccardo Campana, Mauro Centrone, Giovanni De Cesare, Sergio Di Cosimo, Giuseppe Di Persio, Alessandro Lacerenza, Pasqualino Loffredo, Gabriele Minervini, Fabio Muleri, Paolo Romano, Emanuele Scalise, Enrico Silva, Davide Albanesi, Ilaria Baffo, Daniele Brienza, Valerio Campomaggiore, Giovanni Cucinella, Andrea Curatolo, Giulia de Iulis, Andrea Del Re, Vito Di Bari, Simone Di Filippo, Immacolata Donnarumma, Pierluigi Fanelli, Nicolas Gagliardi, Paolo Leonetti, Matteo Mergè, Dario Modenini, Andrea Negri, Daniele Pecorella, Massimo Perelli, Alice Ponti, Francesca Sbop, Paolo Tortora, Alessandro Turchi, Valerio Vagelli, Emanuele Zaccagnino, Alessandro Zambardi and Costantino Zazza Show full author list Hide full author list

Particles 2026, 9(1), 4; https://doi.org/10.3390/particles9010004 - 13 Jan 2026

Abstract

Our Sun is the closest X-ray astrophysical source to Earth. As such, it makes for a strong case study to better understand astrophysical processes. Solar flares are particularly interesting as they are linked to coronal mass ejections as well as magnetic field reconnection [...] Read more.

Our Sun is the closest X-ray astrophysical source to Earth. As such, it makes for a strong case study to better understand astrophysical processes. Solar flares are particularly interesting as they are linked to coronal mass ejections as well as magnetic field reconnection sites in the solar atmosphere. Flares can therefore provide insightful information on the physical processes at play on their production sites but also on the emission and acceleration of energetic charged particles towards our planet, making it an excellent forecasting tool for space weather. While solar flares are critical to understanding magnetic reconnection and particle acceleration, their hard X-ray polarization—key to distinguishing between competing theoretical models—remains poorly constrained by existing observations. To address this, we present the CUbesat Solar Polarimeter (CUSP), a mission under development to perform solar flare polarimetry in the 25–100 keV energy range. CUSP consists of a 6U-XL platform hosting a dual-phase Compton polarimeter. The polarimeter is made of a central assembly of four 4 × 4 arrays of plastic scintillators, each coupled to multi-anode photomultiplier tubes, surrounded by four strips of eight elongated GAGG scintillator bars coupled to avalanche photodiodes. Both types of sensors from Hamamatsu are, respectively, read out by the MAROC-3A and SKIROC-2A ASICs from Weeroc. In this manuscript, we present the preliminary spectral performances of single plastic and GAGG channels measured in a laboratory using development boards of the ASICs foreseen for the flight model. Full article

(This article belongs to the Special Issue Advances in Space AstroParticle Physics: Frontier Technologies for Particle Measurements in Space, 2025 Edition)

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10 pages, 5795 KB

Open AccessTechnical Note

The X and Gamma-Ray Imager and Spectrometer Onboard THESEUS—Status and Technological Progresses

by Giulia Mattioli, Claudio Labanti, Enrico Virgilli, Lorenzo Amati, Riccardo Campana, Giuseppe Baldazzi, Smiriti Srivastava, Edoardo Borciani, Paolo Calabretto, Ezequiel J. Marchesini, Ajay Sharma, Evgeny Demenev, Francesco Ficorella, David Novel, Giancarlo Pepponi, Giovanni La Rosa, Paolo Nogara and Giuseppe Sottile

Particles 2026, 9(1), 3; https://doi.org/10.3390/particles9010003 - 8 Jan 2026

Abstract

Gamma-Ray Bursts (GRBs) are intense bursts of high-energy photons which, in just a few seconds, outshine all other

γ

-ray emitters in the sky. Due to their extreme luminosity, GRBs are not only important as high-energy astrophysical phenomena but also serve as valuable [...] Read more.

Gamma-Ray Bursts (GRBs) are intense bursts of high-energy photons which, in just a few seconds, outshine all other

γ

-ray emitters in the sky. Due to their extreme luminosity, GRBs are not only important as high-energy astrophysical phenomena but also serve as valuable probe models of the far, high-redshift Universe. The importance of these events has pushed the High-Energy Astrophysics community to propose new mission concepts over the past decade, prompting dedicated research and development efforts to achieve the required technological readiness levels. The X and Gamma-Ray Imager and Spectrometer (XGIS) is one of the two GRB monitors onboard the proposed, upcoming THESEUS space mission. Building on strong heritage from previous studies, ongoing developments and optimizations are focused on enhancing the instrument’s capabilities and increasing its technological maturity. This work presents the current status of the XGIS instrument and the latest technological advancements achieved in preparation for its deployment on THESEUS. Full article

(This article belongs to the Special Issue Advances in Space AstroParticle Physics: Frontier Technologies for Particle Measurements in Space, 2025 Edition)

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17 pages, 9090 KB

Open AccessArticle

Unlocking the Future of X-Ray Polarimetry with IXPE: Lessons Learned and Next Steps

by Paolo Soffitta, Enrico Costa, Ettore Del Monte, Alessandro Di Marco, Sergio Fabiani, Riccardo Ferrazzoli, Fabio La Monaca, Fabio Muleri, Alda Rubini and Alessio Trois

Particles 2026, 9(1), 2; https://doi.org/10.3390/particles9010002 - 6 Jan 2026

Abstract

This paper discusses issues encountered during the early development of the instrument on the Imaging X-ray Polarimetry Explorer (IXPE), a NASA–ASI Small Explorer mission launched on 9 December 2021. IXPE has observed about 100 sources, yielding meaningful polarimetry for most of them. An [...] Read more.

This paper discusses issues encountered during the early development of the instrument on the Imaging X-ray Polarimetry Explorer (IXPE), a NASA–ASI Small Explorer mission launched on 9 December 2021. IXPE has observed about 100 sources, yielding meaningful polarimetry for most of them. An on-board calibration system mitigated most non-ideal detector behaviors during operations. Data from the on-board polarized and unpolarized X-ray sources are routinely ingested by the flight pipeline to correct the instrument response in a manner transparent to users. Based on its scientific return and payload health, the IXPE mission has been extended through 2028. The lessons learned are informing the design of next-generation X-ray polarimetry missions, as discussed elsewhere in these conferences. Full article

(This article belongs to the Special Issue Advances in Space AstroParticle Physics: Frontier Technologies for Particle Measurements in Space, 2025 Edition)

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11 pages, 2599 KB

Open AccessReview

Review of the Performance of the CMS Hadron Calorimeter

by Yide Wei and Hui Wang

Particles 2026, 9(1), 1; https://doi.org/10.3390/particles9010001 - 2 Jan 2026

Abstract

The hadron calorimeter is a central component of the CMS detector, vital for measuring hadron energies and reconstructing missing transverse momentum. This paper reviews its performance before and after the Phase 1 upgrade (completed in 2019), which upgraded both back-end and front-end electronics, [...] Read more.

The hadron calorimeter is a central component of the CMS detector, vital for measuring hadron energies and reconstructing missing transverse momentum. This paper reviews its performance before and after the Phase 1 upgrade (completed in 2019), which upgraded both back-end and front-end electronics, including photodetectors and charge-integrating ADC with precise-timing TDC, as well as its depth segmentation in the barrel and endcaps. This paper describes energy reconstruction algorithms that suppress out-of-time signals, along with high-precision timing alignment and multi-step energy calibration procedures to mitigate radiation damage and improve energy resolution Performance evaluations using proton–proton collision data demonstrate that the upgraded detector and reconstruction techniques achieve good resolution and robust operation under high-luminosity conditions. Full article

(This article belongs to the Special Issue Selected Papers from the 14th International Conference on New Frontiers in Physics (ICNFP 2025))

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12 pages, 2330 KB

Open AccessArticle

Enhanced Energy Transfer in Resonating Gold Doped Matter Irradiated by Infrared Laser

by Konstantin Zsukovszki and Istvan Papp

Particles 2025, 8(4), 104; https://doi.org/10.3390/particles8040104 - 18 Dec 2025

Abstract

Laser-driven ion acceleration in dense, hydrogen-rich media can be significantly enhanced by embedding metallic nanoantennas that support localized surface plasmon (LSP) resonances. Using large-scale particle-in-cell (PIC) simulations with the EPOCH code, we investigate how nanoantenna geometry and laser pulse parameters influence proton acceleration [...] Read more.

Laser-driven ion acceleration in dense, hydrogen-rich media can be significantly enhanced by embedding metallic nanoantennas that support localized surface plasmon (LSP) resonances. Using large-scale particle-in-cell (PIC) simulations with the EPOCH code, we investigate how nanoantenna geometry and laser pulse parameters influence proton acceleration in gold-doped polymer targets. The study covers dipole, crossed, and advanced 3D-cross antenna configurations under laser intensities of 10¹⁷–10¹⁹ W/cm² and pulse durations from 2.5 to 500 fs, corresponding to experimental conditions at the ELI laser facility. Results show that the dipole antennas exhibit resonance-limited proton energies of ~0.12 MeV, with optimal acceleration at the intensities 4 × 10¹⁷–1 × 10¹⁸ W/cm² and pulse durations around 100–150 fs. This energy is higher by roughly three orders of magnitude than the proton energy for the same field and same polymer without dopes: ~1–2 × 10⁻⁴ MeV. Crossed antennas achieve higher energies (~0.2 MeV) due to dual-mode plasmonic coupling that sustains local fields longer. Advanced 3D and Yagi-like geometries further enhance field localization, yielding proton energies up to 0.4 MeV and larger high-energy proton populations. For dipole antennas, experimental data from ELI exists and our results agree with it. We find that moderate pulses preserve plasmonic resonance for longer and improve energy transfer efficiency, while overly intense pulses disrupt the resonance early. These findings reveal that plasmonic field enhancement and its lifetime govern energy transfer efficiency in laser–matter interaction. Crossed and 3D geometries with optimized spacing enable multimode resonance and sequential proton acceleration, overcoming the saturation limitations of simple dipoles. The results establish clear design principles for tailoring nanoantenna geometry and pulse characteristics to optimize compact, high-energy proton sources for inertial confinement fusion and high-energy-density applications. Full article

(This article belongs to the Special Issue Selected Papers from the 14th International Conference on New Frontiers in Physics (ICNFP 2025))

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12 pages, 610 KB

Open AccessArticle

Insights into the Temperature Parameters from K*⁰ Spectrum in Nuclear Particle Collisions at the Relativistic High-Energy Collider Beam Energies

by Pei-Pin Yang and Abd Haj Ismail

Particles 2025, 8(4), 103; https://doi.org/10.3390/particles8040103 - 15 Dec 2025

Abstract

The blast-wave model with Boltzmann–Gibbs statistics is used to examine the transverse momentum spectra of

{K *}^{0}

mesons generated at the Relativistic High-Energy Collider (RHIC) Beam Energies with mid-rapidity (

| y | < 1

) in symmetric [...] Read more.

The blast-wave model with Boltzmann–Gibbs statistics is used to examine the transverse momentum spectra of

{K *}^{0}

mesons generated at the Relativistic High-Energy Collider (RHIC) Beam Energies with mid-rapidity (

| y | < 1

) in symmetric

A u - A u

collisions. There is a clear correlation between the extracted kinetic freeze-out temperature (

T_{0}

) and transverse flow velocity (

β_{T}

) in various collision centralities and center-of-mass energies (

\sqrt{s_{N N}}

). Since a larger initial energy density delays freeze-out and a shorter system lifetime limits cooling,

T_{0}

is directly proportional to both

\sqrt{s_{N N}}

and peripheral collisions. On the other hand,

β_{T}

drops in peripheral symmetric collisions due to weaker collective expansion, while it rises with

\sqrt{s_{N N}}

because of larger pressure gradients. The concurrence between the thermal and collective energy components in the expanding fireball is reflected in the obvious anti-correlation between

T_{0}

and

β_{T}

. These findings support hydrodynamic predictions and offer important new information about QGP’s freeze-out behavior. Full article

(This article belongs to the Special Issue Advances in QCD: Bridging Heavy-Ion Collisions and Electron Scattering at the Electron-Ion Collider)

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8 pages, 472 KB

Open AccessPerspective

Onboard Machine Learning for High-Energy Observatories for Spacecraft Autonomy and Ground Segment Operations

by Andrea Bulgarelli, Luca Castaldini, Nicolò Parmiggiani, Ambra Di Piano, Riccardo Falco, Alessio Aboudan, Lorenzo Amati, Andrea Argan, Paolo Calabretto, Mauro Dadina, Adriano De Rosa, Valentina Fioretti, Claudio Labanti, Giulia Mattioli, Gabriele Panebianco, Carlotta Pittori, Alessandro Rizzo, Smiriti Srivastava and Enrico Virgilli

Particles 2025, 8(4), 102; https://doi.org/10.3390/particles8040102 - 12 Dec 2025

Abstract

Next-generation space observatories for high-energy gamma-ray astrophysics will increase scientific return using onboard machine learning (ML). This is now possible thanks to today’s low-power, radiation-tolerant processors and artificial intelligence accelerators. This paper provides an overview of current and future ML applications in gamma-ray [...] Read more.

Next-generation space observatories for high-energy gamma-ray astrophysics will increase scientific return using onboard machine learning (ML). This is now possible thanks to today’s low-power, radiation-tolerant processors and artificial intelligence accelerators. This paper provides an overview of current and future ML applications in gamma-ray space missions focused on high-energy transient phenomena. We discuss onboard ML use cases that will be implemented in the future, including real-time event detection and classification (e.g., gamma-ray bursts), and autonomous decision-making, such as rapid repointing to transient events or optimising instrument configuration based on the scientific target or environmental conditions. Full article

(This article belongs to the Special Issue Advances in Space AstroParticle Physics: Frontier Technologies for Particle Measurements in Space, 2025 Edition)

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21 pages, 668 KB

Open AccessArticle

The EPSI R&D: Development of an Innovative Electron–Positron Discrimination Technique for Space Applications

by Oscar Adriani, Lucia Baldesi, Eugenio Berti, Pietro Betti, Massimo Bongi, Alberto Camaiani, Massimo Chiari, Raffaello D’Alessandro, Giacomo De Giorgi, Noemi Finetti, Leonardo Forcieri, Elena Gensini, Andrea Paccagnella, Lorenzo Pacini, Paolo Papini, Oleksandr Starodubtsev, Anna Vinattieri and Chiara Volpato

Particles 2025, 8(4), 101; https://doi.org/10.3390/particles8040101 - 12 Dec 2025

Abstract

The study of the antimatter component in cosmic rays is essential for the understanding of their acceleration and propagation mechanisms, and is one of the most powerful tools for the indirect search of dark matter. Current methods rely on magnetic spectrometers for charge-sign [...] Read more.

The study of the antimatter component in cosmic rays is essential for the understanding of their acceleration and propagation mechanisms, and is one of the most powerful tools for the indirect search of dark matter. Current methods rely on magnetic spectrometers for charge-sign discrimination, but these are not suitable for extending measurements to the TeV region within a short timeframe of a few decades. Since most of present and upcoming high-energy space experiments use large calorimeters, it is crucial to develop an alternative charge-sign discrimination technique that can be integrated with them. The Electron/Positron Space Instrument (EPSI) project, a two-year R&D initiative launched in 2023 with EU recovery funds, aims to address this challenge. The basic idea is to exploit the synchrotron radiation emitted by charged particles moving through Earth’s magnetic field. The simultaneous detection of an electron/positron with an electromagnetic calorimeter and synchrotron photons with an X-ray detector is enough to discriminate between the two particles at the event level. The main challenge is to develop an X-ray detector with a very large active area, high X-ray detection efficiency, and a low-energy detection threshold, compliant with space applications. In this paper, we give an overview of the EPSI project, with a focus on the general idea of the detection principle, the concept of the space instrument, and the design of the X-ray detector. Full article

(This article belongs to the Special Issue Advances in Space AstroParticle Physics: Frontier Technologies for Particle Measurements in Space, 2025 Edition)

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27 pages, 640 KB

Open AccessArticle

Neutrino-Pair Bremsstrahlung Due to Electromagnetic Collisions in Neutron Star Cores Revisited

by Peter S. Shternin

Particles 2025, 8(4), 100; https://doi.org/10.3390/particles8040100 - 11 Dec 2025

Abstract

We reconsider the problem of neutrino-pair bremsstrahlung emission originating from the electromagnetic collisions of charged particles in nucleonic (

n p e μ

) neutron star cores. Two limiting cases are considered: (i) protons in the normal state and (ii) protons in the [...] Read more.

We reconsider the problem of neutrino-pair bremsstrahlung emission originating from the electromagnetic collisions of charged particles in nucleonic (

n p e μ

) neutron star cores. Two limiting cases are considered: (i) protons in the normal state and (ii) protons in the superconducting state. In both cases, the dominant contribution to the bremsstrahlung emissivity

Q_{Br}^{em}

comes from the transverse part of in-medium electromagnetic interactions. For non-superconducting matter, we obtain an unusual

Q_{Br}^{em} \propto T^{23 / 3}

temperature dependence due to the dynamical character of plasma screening in the transverse channel, but these are considerably smaller values of

Q_{Br}^{em}

than in previous studies, rendering the considered process unimportant in practice. In contrast, for superconducting and superfluid matter, the neutrino emission processes involving nucleons are suppressed and

Q_{Br}^{em}

due to lepton collisions provides the residual contribution to the neutrino emissivity of neutron star core matter. In the superconducting case, the plasma screening becomes static and the standard

Q_{Br}^{em} \propto T^{8}

temperature scaling is restored. Simple analytical expressions for

Q_{Br}^{em}

in both limiting cases are provided. Full article

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

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13 pages, 1899 KB

Open AccessArticle

Pattern Recognition with Artificial Intelligence in Space Experiments

by Federica Cuna, Maria Bossa, Fabio Gargano and Mario Nicola Mazziotta

Particles 2025, 8(4), 99; https://doi.org/10.3390/particles8040099 - 10 Dec 2025

Abstract

The application of advanced Artificial Intelligence (AI) techniques in astroparticle experiments represents a major advancement in both data analysis and experimental design. As space missions become increasingly complex, integrating AI tools is essential for optimizing system performance and maximizing scientific return. This study [...] Read more.

The application of advanced Artificial Intelligence (AI) techniques in astroparticle experiments represents a major advancement in both data analysis and experimental design. As space missions become increasingly complex, integrating AI tools is essential for optimizing system performance and maximizing scientific return. This study explores the use of Graph Neural Networks (GNNs) within the tracking systems of space-based experiments. A key challenge in track reconstruction is the high level of noise, primarily due to backscattering tracks, which can obscure the identification of primary particle trajectories. We propose a novel GNN-based approach for node-level classification tasks, specifically designed to distinguish primary tracks from backscattered ones within the tracker. In this framework, AI is employed as a powerful tool for pattern recognition, enabling the system to identify meaningful structures within complex tracking data and to discriminate signal from backscattering with higher precision. By addressing these challenges, our work aims to enhance the accuracy and reliability of data interpretation in astroparticle physics through the advanced deep learning techniques. Full article

(This article belongs to the Special Issue Advances in Space AstroParticle Physics: Frontier Technologies for Particle Measurements in Space, 2025 Edition)

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18 pages, 2016 KB

Open AccessArticle

Magnetic Field Amplification and Reconstruction in Rotating Astrophysical Plasmas: Verifying the Roles of α and β in Dynamo Action

by Kiwan Park

Particles 2025, 8(4), 98; https://doi.org/10.3390/particles8040098 - 4 Dec 2025

Abstract

We investigate the

α

and

β

effects in a rotating spherical plasma system relevant to astrophysical contexts. In particular, we focus on how kinetic and magnetic (current) helicities influence the magnetic diffusivity

β

. These coefficients were modeled using three complementary theoretical approaches. [...] Read more.

We investigate the

α

and

β

effects in a rotating spherical plasma system relevant to astrophysical contexts. In particular, we focus on how kinetic and magnetic (current) helicities influence the magnetic diffusivity

β

. These coefficients were modeled using three complementary theoretical approaches. Direct numerical simulation (DNS) data (large-scale magnetic field

\bar{B}

, turbulent velocity

u

, and turbulent magnetic field

b

) were then used to obtain the actual values of

α_{EM - HM}

,

β_{EM - HM}

,

β_{vv - vw}

, and

β_{bb + jb}

. Using these coefficients, we reconstructed

\bar{B}

and compared it with the DNS results. In the kinematic regime, where

\bar{B}

remains weak, all models agree well with DNS. In the nonlinear regime, however, the field reconstructed with

β_{vv - vw}

alone deviates from DNS and grows without bound. Incorporating the turbulent magnetic diffusion term

β_{bb + jb}

suppresses this unphysical growth and restores consistency. Specifically,

{\bar{B}}_{D N S}

saturates at approximately 0.23 in the nonlinear regime. The reconstructed

\bar{B}

using

β_{E M - H M}

saturates at

\bar{B}

∼0.3. When

β_{v v - v w + b b + j b}

(= β_{v v - v w} + β_{b b + j b})

is used,

\bar{B}

varies from about 0.3 to 0.23. These results indicate that kinetic helicity reduces

β

(or provides a negative contribution), thereby amplifying

\bar{B}

, whereas turbulent current helicity, together with turbulent magnetic and kinetic energies, enhances

β

, thus suppressing

\bar{B}

in the nonlinear regime. In this respect, the new form of

β

differs from the conventional one, which acts solely to diffuse the magnetic field. Full article

(This article belongs to the Special Issue Particles and Plasmas in Strong Fields)

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