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30 pages, 25151 KiB

Open AccessArticle

Prospects for Multimessenger Observations of the Shapley Supercluster

by Valentyna Babur, Olexandr Gugnin and Bohdan Hnatyk

Universe 2025, 11(7), 239; https://doi.org/10.3390/universe11070239 - 21 Jul 2025

Viewed by 254

The Shapley Supercluster, one of the largest and most massive structures in the nearby (redshift

z \leq 0.1

) Universe, located approximately 200 Mpc away, is a unique laboratory for high-energy astrophysics. Galaxy clusters that comprise it are promising targets for multimessenger study [...] Read more.

The Shapley Supercluster, one of the largest and most massive structures in the nearby (redshift

z \leq 0.1

) Universe, located approximately 200 Mpc away, is a unique laboratory for high-energy astrophysics. Galaxy clusters that comprise it are promising targets for multimessenger study due to the presence in the intracluster medium of the necessary conditions for the acceleration of cosmic rays up to ultra-high energies and the generation by them of non-thermal electromagnetic and neutrino emission. Using the Shapley Supercluster’s observational data from the recent eROSITA-DE Data Release, we recover the physical parameters of 45 X-ray luminous galaxy clusters and calculate the expected multiwavelength—from radio to very-high-energy γ-ray as well as neutrino emission, with a particular focus on hadronic interactions of accelerated cosmic ray nuclei with the nuclei of the intracluster medium. The results obtained allow verification of cluster models based on multimessenger observations of clusters, especially in

γ

-ray (Fermi-LAT, H.E.S.S., CTAO-South for the Shapley Supercluster case), and neutrino (Ice Cube, KM3NeT). We also estimate the ability of the Shapley Supercluster to manifest as cosmic Zevatrons and show that it can contribute to the PAO Hot Spot in the Cen A region at UHECR energies over 50 EeV. Full article

(This article belongs to the Special Issue Ultra-High-Energy Cosmic Rays)

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22 pages, 1173 KiB

Open AccessArticle

Galactic Cosmic Ray Interaction with the Perseus Giant Molecular Cloud Using Geant4 Monte Carlo Simulation

by Luan Torres and Luiz Augusto Stuani Pereira

Universe 2025, 11(7), 218; https://doi.org/10.3390/universe11070218 - 2 Jul 2025

Viewed by 383

Abstract

Galactic cosmic rays (GCRs), composed of protons and atomic nuclei, are accelerated in sources such as supernova remnants and pulsar wind nebulae, reaching energies up to the PeV range. As they propagate through the interstellar medium, their interactions with dense regions like molecular [...] Read more.

Galactic cosmic rays (GCRs), composed of protons and atomic nuclei, are accelerated in sources such as supernova remnants and pulsar wind nebulae, reaching energies up to the PeV range. As they propagate through the interstellar medium, their interactions with dense regions like molecular clouds produce secondary particles, including gamma-rays and neutrinos. In this study, we use the Geant4 Monte Carlo toolkit to simulate secondary particle production from GCR interactions within the Perseus molecular cloud, a nearby star-forming region. Our model incorporates realistic cloud composition, a wide range of incidence angles, and both hadronic and electromagnetic processes across a broad energy spectrum. The results highlight molecular clouds as significant sites of multi-messenger emissions and contribute to understanding the propagation of GCRs and the origin of diffuse gamma-ray and neutrino backgrounds in the Galaxy. Full article

(This article belongs to the Special Issue Ultra-High Energy Cosmic Rays: Past, Present and Future)

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19 pages, 2592 KiB

Open AccessArticle

Investigating the Variation and Periodicity of TXS 0506+056

by Xianglin Miao and Yunguo Jiang

Universe 2025, 11(7), 204; https://doi.org/10.3390/universe11070204 - 23 Jun 2025

Viewed by 276

Abstract

TXS 0506+056 is a blazar associated with neutrino events. The study on its variation mechanics and periodicity analysis is meaningful to understand other BL Lac objects. The local cross-correlation function (LCCF) analysis presents a 3

σ

correlation in both the

γ

-ray versus [...] Read more.

TXS 0506+056 is a blazar associated with neutrino events. The study on its variation mechanics and periodicity analysis is meaningful to understand other BL Lac objects. The local cross-correlation function (LCCF) analysis presents a 3

σ

correlation in both the

γ

-ray versus optical and optical versus radio light curves. The time lag analysis suggests that the optical and

γ

-ray band share the same emission region, located upstream of the radio band in the jet. We use both the weighted wavelet Z-transform and generalized Lomb–Scargle methods to analyze the periodicity. We find two plausible quasi-periodic oscillations (QPOs) at

506_{- 56}^{+ 133}

days and

175_{- 7}^{+ 15}

days for the light curve of the optical band. For the

γ

-ray band, we find that the spectrum varies with the softer when brighter (SWB) trend, which could be explained naturally if a stable very high energy component exists. For the optical band, TXS 0506+056 exhibits a harder when brighter (HWB) trend. We discover a trend transition from HWB to SWB in the X-ray band, which could be modeled by the shift in peak frequency assuming that the X-ray emission is composed of the synchrotron and the inverse Compton (IC) components. The flux correlations of

γ

-ray and optical bands behave anomalously during the period of neutrino events, indicating that there are possible other hadronic components associated with neutrino. Full article

(This article belongs to the Special Issue Blazar Bursts: Theory and Observation)

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24 pages, 576 KiB

Open AccessArticle

Asymmetry in the Mean Free Path of Neutrinos in Hot Neutron Matter Under Strong Magnetic Fields

by Eduardo Bauer and Vanesa D. Olivera

Symmetry 2025, 17(6), 896; https://doi.org/10.3390/sym17060896 - 6 Jun 2025

Viewed by 306

Abstract

We investigate the asymmetry in the mean free path of massive neutrinos propagating through hot neutron matter under strong magnetic fields. The system is studied at temperatures up to 30 MeV and baryon densities up to ρ/ρ₀ = 2.5, where [...] Read more.

We investigate the asymmetry in the mean free path of massive neutrinos propagating through hot neutron matter under strong magnetic fields. The system is studied at temperatures up to 30 MeV and baryon densities up to ρ/ρ₀ = 2.5, where ρ₀ is the nuclear saturation density. Magnetic field strengths up to B = 10¹⁸ G are considered. We analyze three different equations of state: one corresponding to a non-interacting Fermi gas and two derived from Skyrme-type interactions. The impact of a finite neutrino mass is assessed and found to be negligible within the energy range considered. The neutrino mean free path is computed for various angles of incidence with respect to the magnetic field direction, revealing a clear angular asymmetry. We show that quantum interference terms contribute significantly to this asymmetry, enhancing neutrino emission in directions perpendicular to the magnetic field at high densities. This result contrasts with previous expectations and suggests a revised interpretation of neutrino transport in magnetized nuclear matter. Full article

(This article belongs to the Special Issue Neutrino Physics and Symmetries)

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12 pages, 4926 KiB

Open AccessArticle

Radio Detection of UHE Cosmic Rays and Neutrinos off the Moon with Two 30 m Telescopes

by Linjie Chen, Jianli Zhang, Lihong Geng and Lingmei Cheng

Universe 2025, 11(1), 7; https://doi.org/10.3390/universe11010007 - 28 Dec 2024

Viewed by 721

Abstract

Due to the Askaryan effect, radio emissions will be produced when ultra-high-energy (UHE) cosmic rays and neutrinos impact the lunar regolith. Many experiments have been proposed and performed to detect such radio emissions from the lunar regolith. However, none of the Cherenkov radio [...] Read more.

Due to the Askaryan effect, radio emissions will be produced when ultra-high-energy (UHE) cosmic rays and neutrinos impact the lunar regolith. Many experiments have been proposed and performed to detect such radio emissions from the lunar regolith. However, none of the Cherenkov radio signals has been detected in these experiments up to now. In order to improve the detectability of the UHE particles, we proposed an experiment to carry out the radio observations of the UHE cosmic rays and neutrinos with two 30 m telescopes for a far longer time than the present experiments. The expected sensitivity for the detection of such UHE particles has been calculated, both for cosmic rays and neutrinos. The results show that a few UHE particle events above 10²⁰ eV could be detected with the expected observation time of several thousand hours. Full article

(This article belongs to the Special Issue Ultra-High-Energy Cosmic Rays)

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19 pages, 490 KiB

Open AccessReview

Pulsar Kick: Status and Perspective

by Gaetano Lambiase and Tanmay Kumar Poddar

Symmetry 2024, 16(12), 1649; https://doi.org/10.3390/sym16121649 - 13 Dec 2024

Cited by 2 | Viewed by 841

Abstract

The high speeds seen in rapidly rotating pulsars after supernova explosions present a longstanding puzzle in astrophysics. Numerous theories have been suggested over the years to explain this sudden “kick” imparted to the neutron star, yet each comes with its own set of [...] Read more.

The high speeds seen in rapidly rotating pulsars after supernova explosions present a longstanding puzzle in astrophysics. Numerous theories have been suggested over the years to explain this sudden “kick” imparted to the neutron star, yet each comes with its own set of challenges and limitations. Key explanations for pulsar kicks include hydrodynamic instabilities in supernovae, anisotropic neutrino emission, asymmetries in the magnetic field, binary system disruption, and physics beyond the Standard Model. Unraveling the origins of pulsar kicks not only enhances our understanding of supernova mechanisms but also opens up possibilities for exploring new physics. In this brief review, we will introduce pulsar kicks, examine the leading hypotheses, and explore future directions for this intriguing phenomenon. Full article

(This article belongs to the Section Physics)

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13 pages, 690 KiB

Open AccessArticle

The Impact of Electron Phase Shifts on ββ-Decay Kinematics

by Ovidiu Niţescu, Stefan Ghinescu and Fedor Šimkovic

Universe 2024, 10(12), 442; https://doi.org/10.3390/universe10120442 - 30 Nov 2024

Viewed by 854

Abstract

We reexamine the angular correlation between the emitted electrons in the double beta decay (DBD) of ¹⁰⁰Mo, with particular attention to the impact of electronic wave function phase shifts. In the two-neutrino mode, the angular correlation factor increases modestly compared to calculations [...] Read more.

We reexamine the angular correlation between the emitted electrons in the double beta decay (DBD) of ¹⁰⁰Mo, with particular attention to the impact of electronic wave function phase shifts. In the two-neutrino mode, the angular correlation factor increases modestly compared to calculations without phase shifts. However, a more detailed analysis of the angular correlation energy distributions uncovered a striking feature: electrons are most likely emitted in the same direction when one of them is below a certain energy threshold. We show that this feature is absent in previous Standard Model (SM) predictions and that phase shifts could also influence the angular correlations predicted by new physics models in two-neutrino DBD. For the neutrinoless mode, the direction flip is also present when phase shifts are included in the calculation. However, the angular correlation factor does not change much when phase shifts are taken into account, though our analysis is limited to the light neutrino exchange as the dominant mechanism. These findings highlight the subtle yet significant role that phase shifts can play in shaping electron emission patterns, influencing both SM and new physics predictions in DBD. Full article

(This article belongs to the Special Issue Exploring Double Beta Decay: Probing Fundamental Properties of Neutrinos and Beyond)

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19 pages, 3178 KiB

Open AccessReview

Exploring the Components of Cosmogenic UHECR, Neutrino, and Diffuse Gamma Ray from High-Energy Astrophysical Objects

by Fangsheng Min, Hong Lu and Yiqing Guo

Galaxies 2024, 12(6), 77; https://doi.org/10.3390/galaxies12060077 - 18 Nov 2024

Viewed by 1062

Abstract

The development of multimessenger astrophysics allows us to probe various background particles from the distant early universe. Up to now, much effort has been made researching the emission and radiation of diverse steady or transient astrophysical sources. We review the potential accelerating, escaping, [...] Read more.

The development of multimessenger astrophysics allows us to probe various background particles from the distant early universe. Up to now, much effort has been made researching the emission and radiation of diverse steady or transient astrophysical sources. We review the potential accelerating, escaping, propagating, and radiation process of high-energy particles under specific circumstances for regular astrophysical sources and briefly discuss the underlying contribution from their emissions to the intensity of ultrahigh-energy cosmic ray, TeV-PeV cosmic neutrino, and the diffuse gamma-ray background, aiming to find a possible common origin. Full article

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35 pages, 7319 KiB

Open AccessArticle

Searching for Hadronic Signatures in the Time Domain of Blazar Emission: The Case of Mrk 501

by Margaritis Chatzis, Stamatios I. Stathopoulos, Maria Petropoulou and Georgios Vasilopoulos

Universe 2024, 10(10), 392; https://doi.org/10.3390/universe10100392 - 10 Oct 2024

Cited by 1 | Viewed by 1030

Abstract

Blazars—a subclass of active galaxies—are intrinsically time-variable broadband sources of electromagnetic radiation. In this contribution, we explored relativistic proton (hadronic) signatures in the time domain blazar emission and searched for those parameter combinations that unveil their presence during flaring epochs. We generated time [...] Read more.

Blazars—a subclass of active galaxies—are intrinsically time-variable broadband sources of electromagnetic radiation. In this contribution, we explored relativistic proton (hadronic) signatures in the time domain blazar emission and searched for those parameter combinations that unveil their presence during flaring epochs. We generated time series for key model parameters, like magnetic field strength and the power-law index of radiating particles, which were motivated from a simulated time series with statistical properties describing the observed GeV gamma-ray flux. We chose the TeV blazar Mrk 501 as our test case, as it had been the study ground for extensive investigations during individual flaring events. Using the code LeHaMoC, we computed the electromagnetic and neutrino emissions for a period of several years that contained several flares of interest. We show that for both of those particle distributions the power-law index variations that were tied to moderate changes in the magnetic field strength of the emitting region might naturally lead to hard X-ray flares with very-high-energy

γ

-ray counterparts. We found spectral differences measurable by the Cherenkov Telescope Array Observatory at sub-TeV energies, and we computed the neutrino fluence over 14.5 years. The latter predicted ∼0.2 muon and anti-muon neutrinos, consistent with the non-detection of high-energy neutrinos from Mrk 501. Full article

(This article belongs to the Special Issue Blazar Bursts: Theory and Observation)

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16 pages, 900 KiB

Open AccessArticle

Black Hole’s Spin-Dependence of γ-Ray and Neutrino Emissions from MAXI J1820+070, XTE J1550-564, and XTE J1859+226

by Dimitrios Rarras, Odysseas Kosmas, Theodora Papavasileiou and Theocharis Kosmas

Particles 2024, 7(3), 818-833; https://doi.org/10.3390/particles7030049 - 12 Sep 2024

Cited by 2 | Viewed by 1394

Abstract

A black hole’s spin effects on the jet emissions of high-energy neutrinos and

γ

-rays from black hole X-ray binary systems (BHXRBs) are investigated. The BHXRBs consist of a stellar black hole, a companion (donor) star, a BH accretion disk, a BH corona, [...] Read more.

A black hole’s spin effects on the jet emissions of high-energy neutrinos and

γ

-rays from black hole X-ray binary systems (BHXRBs) are investigated. The BHXRBs consist of a stellar black hole, a companion (donor) star, a BH accretion disk, a BH corona, and two jets emitted from the black hole perpendicular to the accretion disk. For their description, properties of the accretion disk, specifically the accretion disk’s inner radius

R_{i n}

and the accretion disk’s temperature profile

T (R)

, play key roles since they depend on the black hole’s dimensionless spin parameter

α_{*}

. In this work, we focus on the main reaction mechanisms taking place inside jets from which high-energy

γ

-rays and neutrinos are created. The intensities and integral fluxes of neutrinos and

γ

-rays are obtained by integrating the respective source functions. Lastly, the

γ

-ray absorption due to

e^{-}

-

e^{+}

pair production is considered, particularly absorption from the accretion disk. For concrete applications, we have chosen the BHXRB systems MAXI J1820+070, XTE J1550-564, and XTE J1859+226. Full article

(This article belongs to the Special Issue Testing Fundamental QED and BSM Physics Theories in Leptonic and Hadronic Processes)

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13 pages, 324 KiB

Open AccessArticle

Galactic Stellar Black Hole Binaries: Spin Effects on Jet Emissions of High-Energy Gamma-Rays

by Dimitrios Rarras, Theocharis Kosmas, Theodora Papavasileiou and Odysseas Kosmas

Particles 2024, 7(3), 792-804; https://doi.org/10.3390/particles7030046 - 3 Sep 2024

Cited by 2 | Viewed by 1765

Abstract

In the last few decades, galactic stellar black hole X-ray binary systems (BHXRBs) have aroused intense observational and theoretical research efforts specifically focusing on their multi-messenger emissions (radio waves, X-rays,

γ

-rays, neutrinos, etc.). In this work, we investigate jet emissions of high-energy [...] Read more.

In the last few decades, galactic stellar black hole X-ray binary systems (BHXRBs) have aroused intense observational and theoretical research efforts specifically focusing on their multi-messenger emissions (radio waves, X-rays,

γ

-rays, neutrinos, etc.). In this work, we investigate jet emissions of high-energy neutrinos and gamma-rays created through several hadronic and leptonic processes taking place within the jets. We pay special attention to the effect of the black hole’s spin (Kerr black holes) on the differential fluxes of photons originating from synchrotron emission and inverse Compton scattering and specifically on their absorption due to the accretion disk’s black-body radiation. The black hole’s spin (dimensionless spin parameter

a_{*}

) enters into the calculations through the radius of the innermost circular orbit around the black hole, the

R_{I S C O}

parameter, assumed to be the inner radius of the accretion disk, which determines its optical depth

τ_{d i s k}

. In our results, the differential photon fluxes after the absorption effect are depicted as a function of the photon energy in the range

1

GeV

\leq E \leq 10^{3}

GeV. It is worth noting that when the black holes’ spin (

α_{*}

) increases, the differential photon flux becomes significantly lower. Full article

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33 pages, 7875 KiB

Open AccessReview

A Very-High-Energy Gamma-Ray View of the Transient Sky

by Alessandro Carosi and Alicia López-Oramas

Universe 2024, 10(4), 163; https://doi.org/10.3390/universe10040163 - 29 Mar 2024

Cited by 1 | Viewed by 2287

Abstract

The development of the latest generation of Imaging Atmospheric Cherenkov Telescopes (IACTs) over recent decades has led to the discovery of new extreme astrophysical phenomena in the very-high-energy (VHE, E > 100 GeV) gamma-ray regime. Time-domain and multi-messenger astronomy are inevitably connected to [...] Read more.

The development of the latest generation of Imaging Atmospheric Cherenkov Telescopes (IACTs) over recent decades has led to the discovery of new extreme astrophysical phenomena in the very-high-energy (VHE, E > 100 GeV) gamma-ray regime. Time-domain and multi-messenger astronomy are inevitably connected to the physics of transient VHE emitters, which show unexpected (and mostly unpredictable) flaring or exploding episodes at different timescales. These transients often share the physical processes responsible for the production of the gamma-ray emission, through cosmic-ray acceleration, magnetic reconnection, jet production and/or outflows, and shocks interactions. In this review, we present an up-to-date overview of the VHE transients field, spanning from novae to supernovae, neutrino counterparts or fast radio bursts, among others, and we outline the expectations for future facilities. Full article

(This article belongs to the Special Issue Recent Advances in Gamma Ray Astrophysics and Future Perspectives)

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29 pages, 3630 KiB

Open AccessReview

Scientific Highlights of the AGILE Gamma-ray Mission

by Stefano Vercellone, Carlotta Pittori and Marco Tavani

Universe 2024, 10(4), 153; https://doi.org/10.3390/universe10040153 - 25 Mar 2024

Cited by 1 | Viewed by 1582

Abstract

The

γ

-ray sky above a few tens of megaelectronvolts (MeV) reveals some of the most powerful and energetic phenomena of our Universe. The Astrorivelatore Gamma ad Immagini LEggero (AGILE) Gamma-ray Mission was launched in 2007 with the aim of observing celestial sources [...] Read more.

The

γ

-ray sky above a few tens of megaelectronvolts (MeV) reveals some of the most powerful and energetic phenomena of our Universe. The Astrorivelatore Gamma ad Immagini LEggero (AGILE) Gamma-ray Mission was launched in 2007 with the aim of observing celestial sources by means of three instruments covering a wide range of energies, from hard X-rays up to 30 GeV. Thanks to its wide field of view, AGILE set to observe and detect emission from pulsars, pulsar wind nebulae, gamma-ray bursts, active galactic nuclei, fast radio bursts, terrestrial gamma-ray flashes, and the electromagnetic counterparts of neutrinos and gravitational waves. In particular, the fast on-ground processing and analysis chain allowed the AGILE team to promptly respond to transient events, and activate or participate in multiwavelength observing campaigns. Eventually, after 17 years of operations, the AGILE Italian scientific satellite re-entered the atmosphere on 14 February 2024, ending its intense activity as a hunter of some of the most energetic cosmic sources in the Universe that emit X and

γ

-rays. We will review the most relevant AGILE results to date and their impact on the advancements of theoretical models. Full article

(This article belongs to the Special Issue Recent Advances in Gamma Ray Astrophysics and Future Perspectives)

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32 pages, 733 KiB

Open AccessReview

High-Energy and Ultra-High-Energy Neutrino Astrophysics

by Damiano F. G. Fiorillo

Universe 2024, 10(3), 149; https://doi.org/10.3390/universe10030149 - 20 Mar 2024

Cited by 2 | Viewed by 2225

Abstract

The origin of high-energy cosmic rays, and their behavior in astrophysical sources, remains an open question. Recently, new ways to address this question have been made possible by the observation of a new astrophysical messenger, namely neutrinos. The IceCube telescope has detected a [...] Read more.

The origin of high-energy cosmic rays, and their behavior in astrophysical sources, remains an open question. Recently, new ways to address this question have been made possible by the observation of a new astrophysical messenger, namely neutrinos. The IceCube telescope has detected a diffuse flux of astrophysical neutrinos in the TeV-PeV energy range, likely produced in astrophysical sources accelerating cosmic rays, and more recently it has reported on a few candidate individual neutrino sources. Future experiments will be able to improve on these measurements quantitatively, by the detection of more events, and qualitatively, by extending the measurement into the EeV energy range. In this paper, we review the main features of the neutrino emission and sources observed by IceCube, as well as the main candidate sources that could contribute to the diffuse neutrino flux. As a parallel question, we review the status of high-energy neutrinos as a probe of Beyond the Standard Model physics coupling to the neutrino sector. Full article

(This article belongs to the Special Issue Neutrinos across Different Energy Scales)

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14 pages, 338 KiB

Open AccessArticle

Z Boson Emission by a Neutrino in de Sitter Expanding Universe

by Mihaela-Andreea Băloi, Cosmin Crucean and Diana Dumitrele

Particles 2024, 7(1), 275-288; https://doi.org/10.3390/particles7010016 - 19 Mar 2024

Cited by 2 | Viewed by 1481

Abstract

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. Full article

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

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