Abstracts of Interest
Selected by:
Robert Christian Koenig
Abstract: 2502.04508
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Title:Clash of the Titans: ultra-high energy KM3NeT event versus IceCube data
View PDF HTML (experimental)Abstract:KM3NET has reported the detection of a remarkably high-energy through-going muon. Lighting up about a third of the detector, this muon could originate from a neutrino exceeding 10 PeV energy. The crucial question we need to answer is where this event comes from and what its source is. Intriguingly, IceCube has been running with a much larger effective area for a much longer time, and yet it has not reported neutrinos above 10 PeV. We quantify the tension between the KM3NeT event with the absence of similar high-energy events in IceCube. Through a detailed analysis, we determine the most likely neutrino energy to be in the range 23-2400 PeV. We find a $3.8\sigma$ tension between the two experiments assuming the neutrino to be from the diffuse isotropic neutrino background. Alternatively, assuming the event is of cosmogenic origin and considering three representative models, this tension still falls within 3.2-3.9$\sigma$. The least disfavored scenario is a steady or transient point source, though still leading to $2.9\sigma$ and $2.1\sigma$ tensions, respectively. The lack of observation of high-energy events in IceCube seriously challenges the explanation of this event coming from any known diffuse fluxes. Our results indicate the KM3NeT event is likely the first observation of a new astrophysical source.
Abstract: 2502.06646
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Title:Cosmic electron spectra by the Voyager instruments and the Galactic electrostatic field
View PDF HTML (experimental)Abstract:The Voyager spacecrafts have been measuring since 2012 the rates of electron and nuclei of the cosmic radiation beyond the solar cavity at a distance of more than $10^{13}$ $meters$ from the Earth. A record of unique and notable findings have been reported and, among them, the electron-to-proton flux ratio of 50 to 100 below energies of $50$ $MeV$. This ratio is thoroughly opposite of that of 0.01 measured at higher energies in the range 10 $GeV$ to 10 $TeV$. The difference amounts to four orders of magnitude. Arguments and calculations to show how this surprising and fundamental ratio lends support to the empirical evidence of the ubiquitous electrostatic field in the Milky Way Galaxy are presented. In other respects this paper examines and calculates, for the first time, the electric charge balance in the solar system delimited by the $termination$ $shock$ of the solar wind.
Abstract: 2502.05657
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Title:Ideas and Requirements for the Global Cosmic-Ray Observatory (GCOS)
View PDF HTML (experimental)Abstract:After a successful kick-off meeting in 2021. two workshops in 2022 and 2023 on the future Global Cosmic-Ray Observatory (GCOS) focused mainly on a straw man design of the detector and science possibilities for astro- and particle physics. About 100 participants gathered for in-person and hybrid panel discussions. In this report, we summarize these discussions, present a preliminary straw-man design for GCOS and collect short write-ups of the flash talks given during the focus sessions.
Abstract: 2502.07421
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Title:Stereograph: Stereoscopic event reconstruction using graph neural networks applied to CTAO
View PDF HTML (experimental)Abstract:The CTAO (Cherenkov Telescope Array Observatory) is an international observatory currently under construction. With more than sixty telescopes, it will eventually be the largest and most sensitive ground-based gamma-ray observatory. CTAO studies the high-energy universe by observing gamma rays emitted by violent phenomena (supernovae, black hole environments, etc.). These gamma rays produce an atmospheric shower when entering the atmosphere, which emits faint blue light, observed by CTAO's highly sensitive cameras. The event reconstruction consists of analyzing the images produced by the telescopes to retrieve the physical properties of the incident particle (mainly direction, energy, and type). A standard method for performing this reconstruction consists of combining traditional image parameter calculations with machine learning algorithms, such as random forests, to estimate the particle's energy and class probability for each telescope. A second step, called stereoscopy, combines these monoscopic reconstructions into a global one using weighted averages. In this work, we explore the possibility of using Graph Neural Networks (GNNs) as a suitable solution for combining information from each telescope. The "graph" approach aims to link observations from different telescopes, allowing analysis of the shower from multiple angles and producing a stereoscopic reconstruction of the events. We apply GNNs to CTAO-simulated data from the Northern Hemisphere and show that they are a very promising approach to improving event reconstruction, providing a more performant stereoscopic reconstruction. In particular, we observe better energy and angular resolutions(before event selection) and better separation between gamma photons and protons compared to the Random Forest method.
Abstract: 2502.06944
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Title:Emergence of a neutrino flux above 5 PeV and implications for ultrahigh energy cosmic rays
View PDF HTML (experimental)Abstract:The rare detections of astrophysical neutrinos with energies above 5~PeV by two neutrino telescopes underscore the existence of a flux at these energies. In addition to over a decade of data taken by the IceCube Neutrino Observatory, the KM3NeT neutrino telescope has recently highlighted their discovery of a possible $\mathcal{O}(100~PeV)$ neutrino candidate. A connection between the highest-energy astrophysical neutrinos and the highest-energy cosmic rays is expected, and well-established theoretically. Here, for the first time, we simultaneously fit the neutrino data from IceCube and KM3NeT, as well as the ultrahigh-energy cosmic ray spectrum and composition data from the Pierre Auger Observatory (Auger), to test a common-origin hypothesis. We show that a phenomenological model is able to describe the combined data across these three observatories, and, depending on the true energy of the event detected by KM3NeT, suggests an additional cosmic ray source population not yet robustly detected by Auger. Although a measurement of the neutrino flux in this energy regime is at the sensitivity limit of cubic-kilometer-scale neutrino telescopes, next-generation observatories, such IceCube-Gen2, will have the sensitivity to make a significant detection of this flux.
Abstract: 2502.06935
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Title:Collective flavor conversions are interactions of neutrinos with quantized flavor waves
View PDF HTML (experimental)Abstract:Collective oscillations in dense neutrino gases (flavor waves) are notable for their instabilities that cause fast flavor conversion. We develop a quantum theory of interacting neutrinos and flavor wave quanta, which are analogous to plasmons, but also carry flavor. The emission or absorption of such flavor plasmons $\psi$, or flavomons, changes the neutrino flavor. When an angular crossing occurs, the process $\nu_\mu\to\nu_e+\psi$ is more rapid than its inverse along the direction of the crossing, triggering stimulated $\psi$ emission and fast instability. Calculating the rate via Feynman diagrams matches the fast instability growth rate. Our novel $\nu$ and $\psi$ kinetic equations, corresponding to quasi-linear theory, describe instability evolution without resolving the small scales of the flavomon wavelength, potentially overcoming the main challenge of fast flavor evolution.
Abstract: 2502.08508
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Title:On the potential cosmogenic origin of the ultra-high-energy event KM3-230213A
View PDF HTML (experimental)Abstract:On the 13th February 2023 the KM3NeT/ARCA telescope observed a track-like event compatible with a ultra-high-energy muon with an estimated energy of 120 PeV, produced by a neutrino with an even higher energy, making it the most energetic neutrino event ever detected. A diffuse cosmogenic component is expected to originate from the interactions of ultra-high-energy cosmic rays with ambient photon and matter fields. The flux level required by the KM3NeT/ARCA event is however in tension with the standard cosmogenic neutrino predictions based on the observations collected by the Pierre Auger Observatory and Telescope Array over the last decade of the ultra-high-energy cosmic rays above the ankle (hence from the local Universe, $z\lesssim 1$). We show here that both observations can be reconciled by extending the integration of the equivalent cosmogenic neutrino flux up to a redshift of $z\simeq 6$ and assuming a subdominant fraction of protons in the ultra-high-energy cosmic-ray flux, thus placing constraints on known cosmic accelerators.
Abstract: 2502.08484
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Title:Characterising Candidate Blazar Counterparts of the Ultra-High-Energy Event KM3-230213A
View PDF HTML (experimental)Abstract:The KM3NeT experiment reported the detection of an ultra-high-energy neutrino with an energy estimate of ~ 220 PeV, the most energetic yet observed. The neutrino arrival direction has a 99% confidence region of 3° radius centred at RA 94.3°, Dec -7.8° (J2000). High-energy astrophysical neutrinos are a crucial messenger for understanding hadronic acceleration processes in the Universe and for identifying the origin of ultra-high-energy cosmic rays. Among the most powerful cosmic accelerators, blazars are proposed as promising neutrino sources. A sample of seventeen candidate blazars located in this region is selected through their multiwavelength properties, and studied using archival data and dedicated observations. One of the candidate counterparts exhibits a radio flare coinciding with the neutrino arrival time, with a pre-trial chance probability of 0.26%. Another candidate counterpart exhibits a rising trend in the X-ray flux in a one-year window around the neutrino arrival time. A third candidate undergoes a gamma-ray flare during the same period. While none of these candidates can conclusively be linked to the neutrino, the implications of a possible blazar origin for the KM3NeT event are discussed.
Abstract: 2502.08387
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Title:On the Potential Galactic Origin of the Ultra-High-Energy Event KM3-230213A
View PDF HTML (experimental)Abstract:The KM3NeT observatory detected the most energetic neutrino candidate ever observed, with an energy between 72 PeV and 2.6 EeV at the 90% confidence level. The observed neutrino is likely of cosmic origin. In this article, it is investigated if the neutrino could have been produced within the Milky Way. Considering the low fluxes of the Galactic diffuse emission at these energies, the lack of a nearby potential Galactic particle accelerator in the direction of the event and the difficulty to accelerate particles to such high energies in Galactic systems, we conclude that if the event is indeed cosmic, it is most likely of extragalactic origin.
Abstract: 2502.08173
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Title:The ultra-high-energy event KM3-230213A within the global neutrino landscape
View PDF HTML (experimental)Abstract:On February 13th, 2023, the KM3NeT/ARCA telescope detected a neutrino candidate with an estimated energy in the hundreds of PeVs. In this article, the observation of this ultra-high-energy neutrino is discussed in light of null observations above tens of PeV from the IceCube and Pierre Auger observatories. Performing a joint fit of all experiments under the assumption of an isotropic $E^{-2}$ flux, the best-fit single-flavour flux normalisation is $E^2 \Phi^{\rm 1f}_{\nu + \bar \nu} = 7.5 \times 10^{-10}~{\rm GeV cm^{-2} s^{-1} sr^{-1}}$ in the 90% energy range of the KM3NeT event. Furthermore, the ultra-high-energy data are then fit together with the IceCube measurements at lower energies, either with a single power law or with a broken power law, allowing for the presence of a new component in the spectrum. The joint fit including non-observations by other experiments in the ultra-high-energy region shows a slight preference for a break in the PeV regime if the ``High-Energy Starting Events'' sample is included, and no such preference for the other two IceCube samples investigated. A stronger preference for a break appears if only the KM3NeT data is considered in the ultra-high-energy region, though the flux resulting from such a fit would be inconsistent with null observations from IceCube and Pierre Auger. In all cases, the observed tension between KM3NeT and other datasets is of the order of $2.5\sigma-3\sigma$, and increased statistics are required to resolve this apparent tension and better characterise the neutrino landscape at ultra-high energies.
Abstract: 2502.09545
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Title:Cascaded Gamma-ray Emission Associated with the KM3NeT Ultra-High-Energy Event KM3-230213A
View PDF HTML (experimental)Abstract:A neutrino-like event with an energy of $\sim 220 \,{\rm PeV}$ was recently detected by the KM3NeT/ARCA telescope. If this neutrino comes from an astrophysical source, or from the interaction of an ultra-high-energy cosmic ray in the intergalactic medium, the ultra-high-energy gamma rays that are co-produced with the neutrinos will scatter with the extragalactic background light, producing an electromagnetic cascade and resulting in emission at GeV-to-TeV energies. In this paper, we compute the gamma-ray flux from this neutrino source considering various source distances and strengths of the intergalactic magnetic field (IGMF). We find that the associated gamma-ray emission could be observed by existing imaging air cherenkov telescopes and air shower gamma-ray observatories, unless the strength of the IGMF is $B\gtrsim 3\times 10^{-13}$ G, or the ultra-high-energy gamma-rays are attenuated inside of the source itself. In the latter case, this source is expected to be radio-loud.
Abstract: 2502.09108
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Title:The Influence of Sun's and Moon's Shadows on Cosmic-Ray Anisotropy
View PDF HTML (experimental)Abstract:Large-scale anisotropy, with amplitudes reaching approximately 0.1% at TeV energies, has been observed by multiple cosmic-ray experiments. The obstruction of cosmic rays by the Sun and Moon creates shadow effects, potentially impacting the observed cosmic ray anisotropy. To evaluate these effects, this study calculates the contributions of the Sun's and Moon's shadows to the overall cosmic-ray anisotropy in both local solar and sidereal time. The analysis reveals that in local sidereal time, the total 1D projection amplitude of the anisotropy is around 0.003%, which is significantly smaller than the observed cosmic-ray anisotropy. This indicates that the influence of the Sun's and Moon's shadows on cosmic-ray anisotropy analysis in local sidereal time is negligible. In contrast, in local solar time, the shadow-induced deficit appears in a very small time bin, with a magnitude comparable to that of the cosmic-ray solar anisotropy. This deficit could serve as a benchmark for validating anisotropy measurements in future facilities.
Abstract: 2502.08798
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Title:Modified Hadronic Interactions and the future of UHECR observations
View PDF HTML (experimental)Abstract:Data from multiple experiments suggest that the current interaction models used in Monte Carlo simulations do not correctly reproduce the hadronic interactions in air showers produced by ultra-high-energy cosmic rays (UHECR). We have created a large library of UHECR simulations where the interactions at the highest energies are slightly modified in various ways - but always within the constraints of the accelerator data, without any abrupt changes with energy and without assuming any specific mechanism or dramatically new physics at the ultra-high energies. Recent results of the Pierre Auger Observatory indicate a need for a change in the prediction of the models for both the muon content at ground and the depth of the maximum of longitudinal development of the shower. In our parameter space, we find combinations of modifications that are in agreement with this analysis, however a consistent description of UHECR showers remains elusive. Our library however provides a realistic representation of the freedom in the modeling of the hadronic interactions and offers an opportunity to quantify uncertainties of various predictions. This can be particularly valuable for the design of future observatories where hadronic models are often used as input for the prediction of the performance. We demonstrate this powerful capability on several selected examples.
Abstract: 2502.08747
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Title:Consequences of a Heavy-Metal Scenario of Ultra-High-Energy Cosmic Rays
View PDF HTML (experimental)Abstract:We assume an extreme scenario, in which the arriving cosmic rays are composed of only iron nuclei at energies above $10^{19.6}\,\text{eV}\simeq40\,\text{EeV}$, while allowing a freedom in the scale of the depth of shower maximum ($X_{\rm{max}}$) and preserving the elongation rate and fluctuations of $X_{\rm{max}}$ predicted by models of hadronic interactions. We derive the shift of the $X_{\rm{max}}$ scale for QGSJet II-04 and Sibyll 2.3d models using the public data from the Pierre Auger Observatory. We then propose a new mass-composition model for the energy evolution of four primary species at the ultra-high energies by fitting the publicly-available $X_{\rm{max}}$ distributions. We discuss the consequences of this Heavy-metal scenario on the energy spectrum of individual primary species, hadronic interaction studies, and the effect of the Galactic magnetic field on the arrival directions.
Abstract: 2502.08733
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Title:The spectral shapes of Galactic gamma-ray source
View PDF HTML (experimental)Abstract:Recent observations by ground-based gamma-ray telescopes have led to the publication of catalogs listing sources observed in the TeV and PeV energy ranges. Photons of such high energy are strongly absorbed during propagation over extragalactic distances, and the catalogs are dominated by Galactic sources. Of particular interest are the observations of the LHAASO telescope, which cover a very broad energy range (from 1 to 10$^3$ TeV) and show that the spectra of all Galactic gamma-ray sources are curved, with significantly different slopes below and above $E \sim 30$ TeV. The cumulative spectrum obtained by summing the contributions of Galactic individual sources has a spectral shape that gradually softens with energy, with a slope that increases from a value of order 2.2 at $E \simeq 1$ TeV, to 2.5 at 30 TeV, and $\simeq 3.4$ at 100 TeV. It is remarkable that the smooth variation in the shape of the cumulative spectrum is obtained from the sum of contributions that have a wide range of shapes. Understanding the origin of the spectral shapes of the Galactic gamma-ray sources is a crucial challenge for high energy astrophysics.
Abstract: 2502.09548
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Title:Ultra-high-energy event KM3-230213A constraints on Lorentz Invariance Violation in neutrino sector
View PDF HTML (experimental)Abstract:We discuss the constraints on superluminal neutrino Lorentz Invariance Violation (LIV) parameters from the observation of the ultra-high-energy event KM3-230213A by KM3NeT collaboration in cases of linear $n=1$ and quadratic $n=2$ LIV scenarios. Assuming extragalactic origin of the event, we obtain the constraints on LIV mass scale $\Lambda_{n=1} = 5.4 \times 10^{30}\, \mbox{GeV}$ and $\Lambda_{n=2} = 3.5 \times 10^{19}\, \mbox{GeV}$ from the absence of neutrino splitting.
Abstract: 2502.09260
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Title:Spectral diversity in collisional neutrino-flavor conversion: flavor equipartition or swap
View PDF HTML (experimental)Abstract:Quantum kinetics of neutrinos are known to potentially change the classical neutrino radiation field in high-energy astrophysical sources such as core-collapse supernovae and binary neutron-star mergers. However, the mixing phenomena still have open issues in the nonlinear dynamics and the asymptotic states, particularly for recently discovered collision-induced flavor conversion. In this paper, we investigate linear and nonlinear dynamics of collisional neutrino-flavor conversion (CFC) with multi-energy neutrino gases through numerical simulations, demonstrating that the asymptotic states dramatically change depending on unstable modes dominating the system. In one unstable mode, high-energy neutrinos reach a flavor equipartition, but low-energy neutrinos return back to almost their initial states. In contrast, in the other one, rather low-energy neutrinos achieve a full flavor swap, but high-energy neutrinos undergo less flavor conversion. We clarify the distinct spectral behaviors in two different ways based on stability analysis and flavor pendulum. Our result suggests that CFC with flavor swap can become crucial at deeper radii with low electron fraction and requires more detailed theoretical modeling of neutrino quantum kinetics.
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