Cosmic Neutrinos Research Articles

The IceCube-Gen2 Neutrino Observatory

The IceCube Neutrino Observatory opened the window on neutrino astronomy by discovering high-energy astrophysical neutrinos in 2013 and identifying the first compelling astrophysical neutrino source, the blazar TXS0506 + 056, in 2017. In this proceeding, we will discuss the science reach and ongoing development of the IceCube-Gen2 facility, which is the planned extension to IceCube. IceCube-Gen2 will increase the rate of observed cosmic neutrinos by an order of magnitude, be able to detect five-times fainter neutrino sources, and extend the measurement of astrophysical neutrinos several orders of magnitude higher in energy. We will discuss the envisioned design of the instrument, which will include an enlarged in-ice optical array, a surface array for the study of cosmic-rays, and a shallow radio array to detect ultra-high energy (>100 PeV) neutrinos. We will also highlight ongoing efforts to develop and test new instrumentation for IceCube-Gen2.

High‐Energy Neutrinos from the Cosmos

AbstractThe IceCube project transformed a cubic kilometer of transparent natural Antarctic ice into a Cherenkov detector. It discovered PeV‐energy neutrinos originating beyond our galaxy with an energy flux that is comparable to that of GeV‐energy gamma rays and EeV‐energy cosmic rays. These neutrinos provide the only unobstructed view of the cosmic accelerators that power the highest energy radiation reaching us from the universe. The results from IceCube's first decade of operations, foremost the measurement of the diffuse neutrino flux from the universe using multiple techniques is reviewed. The multimessenger data that identified the supermassive black hole TXS 0506+056 as a source of cosmic neutrinos is subsequently reviewed and attention is drawn to accumulating indications that cosmic neutrinos are associated with gamma‐ray‐obscured active galaxies, that is, the energy in gamma rays that accompanies cosmic neutrinos emerges at MeV energies, or below. Reaching beyond 10 PeV energy, cosmic neutrinos provide a natural beam to study neutrinos themselves.

Searching for the Radiative Decay of the Cosmic Neutrino Background with Line-Intensity Mapping

We study the possibility to use line-intensity mapping (LIM) to seek photons from the radiative decay of neutrinos in the cosmic neutrino background. The Standard Model prediction for the rate for these decays is extremely small, but it can be enhanced if new physics increases the neutrino electromagnetic moments. The decay photons will appear as an interloper of astrophysical spectral lines. We propose that the neutrino-decay line can be identified with anisotropies in LIM clustering and also with the voxel intensity distribution. Ongoing and future LIM experiments will have-depending on the neutrino hierarchy, transition, and experiment considered-a sensitivity to an effective electromagnetic transition moment ∼10^{-12}-10^{-8}(m_{i}c^{2}/0.1 eV)^{3/2}μ_{B}, where m_{i} is the mass of the decaying neutrino and μ_{B} is the Bohr magneton. This will be significantly more sensitive than cosmic microwave background spectral distortions, and it will be competitive with stellar cooling studies. As a by-product, we also report an analytic form of the one-point probability distribution function for neutrino-density fluctuations, obtained from the quijote simulations using symbolic regression.

Neutrino events within muon bundles at neutrino telescopes

The atmospheric neutrino flux includes a component from the prompt decay of charmed hadrons that becomes significant only at E≥10TeV. At these energies, however, the diffuse flux of cosmic neutrinos discovered by IceCube seems to be larger than the atmospheric one. Here we study the possibility to detect a neutrino interaction in down-going atmospheric events at km3 telescopes. The neutrino signal will always appear together with a muon bundle that reveals its atmospheric origin and, generically, it implies an increase in the detector activity with the slant depth. We propose a simple algorithm that could separate these events from regular muon bundles.

Sensitivity estimates for diffuse, point-like, and extended neutrino sources with KM3NeT/ARCA

The identification of cosmic objects emitting high energy neutrinos could provide new insights about the Universe and its active sources. The existence of these cosmic neutrinos has been proven by the IceCube Collaboration, but the big question of which sources these neutrinos originate from, remains unanswered. The KM3NeT detector for Astroparticle Research with Cosmics in the Abyss (ARCA), with a cubic kilometer instrumented volume, is currently being built in the Mediterranean Sea. It will excel at identifying cosmic neutrino sources due to its unprecedented angular resolution for muon neutrinos (< 0.2 degree for E > 10 TeV events). KM3NeT has a view of the sky complementary to IceCube, and is sensitive to neutrinos across a wide range of energies. In order to identify the signature of cosmic neutrino sources in the background of atmospheric neutrinos and muons, statistical methods are being developed and tested with Monte-Carlo pseudo-experiments. This contribution presents the most recent sensitivity estimates for diffuse, point-like, and extended neutrino sources with KM3NeT/ARCA.

Multi-messenger triggered searches with the ANTARES Neutrino Telescope

The ANTARES neutrino telescope has been operating for thirteen years in the Mediterranean sea with the purpose of searching for high-energy cosmic neutrinos. During the last years, multi-messenger astronomy has become one of the most exciting topics for Cherenkov neutrino detectors, and probably the best strategy to identify the neutrino sources. Thus, the ANTARES Collaboration is actively participating to the follow-up of alerts sent by different experiments, covering the full electromagnetic spectrum and gravitational wave interferometers.ANTARES' real-time response to these alerts is complemented with dedicated offline analyses, the latter being the focus of this talk. These studies allowed to set upper limits that constrain the neutrino emission from various sources, including Fast Radio Bursts, Gamma Ray Bursts and compact binary mergers, as well as neutrino alerts by others neutrino observatories (IceCube, GVD). The latest results are presented here.

Nuclearite search with ANTARES

The ANTARES detector is a Cherenkov underwater neutrino telescope operating in the Mediterranean Sea. Its construction was completed in 2008. Even though optimised for the search of cosmic neutrinos, this telescope is also sensitive to nuclearites (massive nuggets of strange quark matter) trough the black body radiation emitted along their path.We discuss here the possible detection of non-relativistic down-going nuclearites with the ANTARES telescope and present the results of an analysis using data collected from 2009 till 2017.

A New Gamma-Ray-emitting Population of FR0 Radio Galaxies

Abstract The enigmatic class of Fanaroff–Riley type 0 (FR0) radio galaxies is emerging as the missing link between the faint yet numerous population of compact radio sources in nearby galaxies and the canonical Fanaroff–Riley classification scheme. This Letter reports the first γ-ray identification of three FR0 galaxies above 1 GeV using more than a decade of the Fermi Large Area Telescope observations. A cumulative γ-ray emission at &gt;5σ significance was also detected from the γ-ray unresolved FR0 sources using the stacking technique, suggesting the FR0 population to be a γ-ray emitter as a whole. The multifrequency properties of the γ-ray-detected sources are similar to other FR0s, thus indicating the high-energy radiation to originate from misaligned jets. Given their large abundance, FR0 radio galaxies are proposed as plausible candidates for IceCube-detected neutrinos and the results presented in this Letter may provide crucial constraints on their γ-ray production mechanism and the origin of cosmic neutrinos.

Constraining the contribution of Gamma-Ray Bursts to the high-energy diffuse neutrino flux with 10 years of ANTARES data

Gamma-Ray Bursts (GRBs) are considered very interesting astrophysical sources to be studied in the context of neutrino astronomy. Indeed, their jet composition continues to be an open issue. Within the framework of the fireball model, mesons can be produced during photo-hadronic interactions occurring in the internal shocks between shells emitted by the central engine. From their decays, high-energy gamma rays and neutrinos are expected to be generated. Neutrino telescopes are particularly interested in GRBs: being the most powerful explosions observable in the Universe, they are potentially able to achieve the energetics required to contribute to the diffuse astrophysical neutrino flux measured few years ago by IceCube. The analysis here presented relies on the search of time and space coincidences between neutrinos and the GRB emission. The undersea neutrino telescope ANTARES, operational in the Northern hemisphere since 2008 in its full configuration, plays an important role in the cosmic neutrino searches. In this contribution, the results of a stacked search for astrophysical muon neutrinos are presented for 784 GRBs in the period 2007-2017 using the ANTARES data. Given the absence of coincidences between a neutrino and a GRB in the considered sample, this analysis has allowed to constrain the contribution of the detected GRB population to the neutrino diffuse flux to be less than 10% around 100 TeV, within the context of the internal shock model. In addition, for the first time in this kind of analysis, the uncertainties on the not well characterised GRB parameters, needed to compute the neutrino flux expectations, are taken into account for each individual burst and then propagated to the diffuse flux from GRBs and to the estimated stacked upper limit.

Cosmic Ray Background Removal With Deep Neural Networks in SBND.

In liquid argon time projection chambers exposed to neutrino beams and running on or near surface levels, cosmic muons, and other cosmic particles are incident on the detectors while a single neutrino-induced event is being recorded. In practice, this means that data from surface liquid argon time projection chambers will be dominated by cosmic particles, both as a source of event triggers and as the majority of the particle count in true neutrino-triggered events. In this work, we demonstrate a novel application of deep learning techniques to remove these background particles by applying deep learning on full detector images from the SBND detector, the near detector in the Fermilab Short-Baseline Neutrino Program. We use this technique to identify, on a pixel-by-pixel level, whether recorded activity originated from cosmic particles or neutrino interactions.

Neutrinos from the cosmic noon: a probe of the cosmic star formation history

Multiple astrophysical probes of the cosmic star formation history (CSFH) indicate a period of peak star formation known as the cosmic noon between 1.5 ≲ z ≲ 3.5.In this work, we explore the potential of future measurements of the diffuse supernova neutrino background (DSNB) at the Hyper-Kamiokande (HK) experiment to be sensitive to variations in the expected star formation rate at cosmic noon. Motivated by a statistically mild discrepancy between Hα and UV/IR probes of the CSFH, which indicate a factor of ∼ 3 difference in the CSFH near the cosmic noon, we construct two benchmark hypotheses based on these different data sets. Since the cosmic noon neutrinos are redshifted to low energies, a low threshold sensitivity of any detector will be critical for discriminating between these benchmark hypotheses. We explore whether HK loaded with Gadolinium, with a positron threshold energy of 10 MeV, would be sensitive to the difference between these two CSFH hypotheses. Assuming that the supernova (SN) neutrino spectrum can be well determined by calibrating core-collapse SNe simulations to observations of nearby SNe, we find that only for very high core-collapse SN temperatures, HK would be sensitive to the difference in the benchmark CSFHs, and even then, over a 10–30 year time scale. Future experiments must lower their thresholds to be more sensitive to cosmic noon neutrinos.

Synergies of THESEUS with the large facilities of the 2030s and guest observer opportunities

The proposed THESEUS mission will vastly expand the capabilities to monitor the high-energy sky. It will specifically exploit large samples of gamma-ray bursts to probe the early universe back to the first generation of stars, and to advance multi-messenger astrophysics by detecting and localizing the counterparts of gravitational waves and cosmic neutrino sources. The combination and coordination of these activities with multi-wavelength, multi-messenger facilities expected to be operating in the 2030s will open new avenues of exploration in many areas of astrophysics, cosmology and fundamental physics, thus adding considerable strength to the overall scientific impact of THESEUS and these facilities. We discuss here a number of these powerful synergies and guest observer opportunities.

Violation of equivalence principle in neutrino sector: probing the extended parameter space

The oscillation of neutrino flavors, due to its interferometry nature, is extremely sensitive to the phase differences developing during the propagation of neutrinos. In this paper we investigate the effect of the Violation of Equivalence Principle (VEP) on the flavor oscillation probabilities of atmospheric and cosmic neutrinos observed at neutrino telescopes such as IceCube. Assuming a general parameterization of VEP, dubbed extended parameter space, we show that the synergy between the collected data of high energy atmospheric and cosmic neutrinos severely constrains the VEP parameters. Also, the projected sensitivity of IceCube-Gen2 to VEP parameters is discussed.

On the \u03c4 flavor of the cosmic neutrino flux

Observation of high energy cosmic neutrinos by ICECUBE has ushered in a new era in exploring both cosmos and new physics beyond the Standard Model (SM). In the standard picture, although mostly νμ and νe are produced in the source, oscillation will produce ντen route. Certain beyond SM scenarios, like interaction with ultralight DM can alter this picture. Thus, the flavor composition of the cosmic neutrino flux can open up the possibility of exploring certain beyond the SM scenarios that are inaccessible otherwise. We show that the τ flavor holds a special place among the neutrino flavors in elucidating new physics. Interpreting the two anomalous events observed by ANITA as ντ events makes the tau flavor even more intriguing. We study how the detection of the two tau events by ICECUBE constrains the interaction of the neutrinos with ultralight dark matter and discuss the implications of this interaction for even higher energy cosmic neutrinos detectable by future radio telescopes such as ARA, ARIANNA and GRAND. We also revisit the 3 + 1 neutrino scheme as a solution to the two anomalous ANITA events and clarify a misconception that exists in the literature about the evolution of high energy neutrinos in matter within the 3 + 1 scheme with a possibility of scattering off nuclei. We show that the existing bounds on the flux of ντ with energy of EeV rules out this solution for the ANITA events. We show that the 3 + 1 solution can be saved from both this bound and from the bound on the extra relativistic degrees of freedom in the early universe by turning on the interaction of neutrinos with ultralight dark matter.

The POEMMA (Probe of Extreme Multi-Messenger Astrophysics) observatory

The Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) is designed to accurately observe ultra-high-energy cosmic rays (UHECRs) and cosmic neutrinos from space with sensitivity over the full celestial sky. POEMMA will observe the air fluorescence produced by extensive air showers (EASs) from UHECRs and potentially UHE neutrinos above 20 EeV. Additionally, POEMMA has the ability to observe the Cherenkov signal from upward-moving EASs induced by Earth-interacting tau neutrinos above 20 PeV. The POEMMA spacecraft are designed to quickly re-orientate to follow up transient neutrino sources and obtain currently unparalleled neutrino flux sensitivity. Developed as a NASA Astrophysics Probe-class mission, POEMMA consists of two identical satellites flying in loose formation in 525 km altitude orbits. Each POEMMA instrument incorporates a wide field-of-view (45∘) Schmidt telescope with an optical collecting area of over 6 m2. The hybrid focal surface of each telescope includes a fast (1 μs) near-ultraviolet camera for EAS fluorescence observations and an ultrafast (10 ns) optical camera for Cherenkov EAS observations. In a 5-year mission, POEMMA will provide measurements that open new multi-messenger windows onto the most energetic events in the universe, enabling the study of new astrophysics and particle physics at these extreme energies.

Multi-messenger astrophysics with the cosmic neutrino background

The massive neutrinos of the Cosmic Neutrino Background (CνB) are fundamental ingredients of the radiation-dominated early universe and are important non-relativistic probes of the large-scale structure formation in the late universe. The dominant source of anisotropies in the neutrino flux distribution on the sky are highly amplified integrals of metric perturbations encountered during the non-relativistic phase of the CνB. This paper numerically compares the line-of-sight methods for computing CνB anisotropies with the Einstein-Boltzmann hierarchy solutions in linear theory for a range of neutrino masses. Angular power spectra are computed that are relevant to a future polarized tritium target run of the PTOLEMY experiment. Correlations between the CνB sky maps and galactic survey data are derived using line-of-sight techniques and discussed in the context of multi-messenger astrophysics.

Self-consistent determination of proton and nuclear PDFs at the Electron Ion Collider

We quantify the impact of unpolarized lepton-proton and lepton-nucleus inclusive deep-inelastic scattering (DIS) cross section measurements from the future Electron-Ion Collider (EIC) on the proton and nuclear parton distribution functions (PDFs). To this purpose, we include neutral- and charged-current DIS pseudodata in a self-consistent set of proton and nuclear global PDF determinations based on the NNPDF methodology. We demonstrate that the EIC measurements will reduce the uncertainty of the light quark PDFs of the proton at large values of the momentum fraction $x$ and, more significantly, of the quark and gluon PDFs of heavy nuclei, especially at small and large $x$. We illustrate the implications of the improved precision of nuclear PDFs for the interaction of ultrahigh energy cosmic neutrinos with matter.

Chiral oscillations in the non-relativistic regime

Massive Dirac particles are a superposition of left and right chiral components. Since chirality is not a conserved quantity, the free Dirac Hamiltonian evolution induces chiral quantum oscillations, a phenomenon related to the Zitterbewegung, the trembling motion of free propagating particles. While not observable for particles in relativistic dynamical regimes, chiral oscillations become relevant when the particle’s rest energy is comparable to its momentum. In this paper, we quantify the effect of chiral oscillations on the non-relativistic evolution of a particle state described as a Dirac bispinor and specialize our results to describe the interplay between chiral and flavor oscillations of non-relativistic neutrinos: we compute the time-averaged survival probability and observe an energy-dependent depletion of the quantity when compared to the standard oscillation formula. In the non-relativistic regime, this depletion due to chiral oscillations can be as large as 40%. Finally, we discuss the relevance of chiral oscillations in upcoming experiments which will probe the cosmic neutrino background.

IceCube-Gen2: the window to the extreme Universe

The observation of electromagnetic radiation from radio to γ-ray wavelengths has provided a wealth of information about the Universe. However, at PeV (1015 eV) energies and above, most of the Universe is impenetrable to photons. New messengers, namely cosmic neutrinos, are needed to explore the most extreme environments of the Universe where black holes, neutron stars, and stellar explosions transform gravitational energy into non-thermal cosmic rays. These energetic particles have millions of times higher energies than those produced in the most powerful particle accelerators on Earth. As neutrinos can escape from regions otherwise opaque to radiation, they allow an unique view deep into exploding stars and the vicinity of the event horizons of black holes. The discovery of cosmic neutrinos with IceCube has opened this new window on the Universe. IceCube has been successful in finding first evidence for cosmic particle acceleration in the jet of an active galactic nucleus. Yet, ultimately, its sensitivity is too limited to detect even the brightest neutrino sources with high significance, or to detect populations of less luminous sources. In this white paper, we present an overview of a next-generation instrument, IceCube-Gen2, which will sharpen our understanding of the processes and environments that govern the Universe at the highest energies. IceCube-Gen2 is designed to:(a) Resolve the high-energy neutrino sky from TeV to EeV energies(b) Investigate cosmic particle acceleration through multi-messenger observations(c) Reveal the sources and propagation of the highest energy particles in the Universe(d) Probe fundamental physics with high-energy neutrinosIceCube-Gen2 will enhance the existing IceCube detector at the South Pole. It will increase the annual rate of observed cosmic neutrinos by a factor of ten compared to IceCube, and will be able to detect sources five times fainter than its predecessor. Furthermore, through the addition of a radio array, IceCube-Gen2 will extend the energy range by several orders of magnitude compared to IceCube. Construction will take 8 years and cost about $350M. The goal is to have IceCube-Gen2 fully operational by 2033.IceCube-Gen2 will play an essential role in shaping the new era of multi-messenger astronomy, fundamentally advancing our knowledge of the high-energy Universe. This challenging mission can be fully addressed only through the combination of the information from the neutrino, electromagnetic, and gravitational wave emission of high-energy sources, in concert with the new survey instruments across the electromagnetic spectrum and gravitational wave detectors which will be available in the coming years.

Oscillations of sterile neutrinos from dark matter decay eliminates the IceCube-Fermi tension

IceCube has observed a flux of cosmic neutrinos, with a "bump" in the energy range $10 \lesssim E/{\rm TeV} \lesssim 100$ that creates a $3\sigma$ tension with gamma-ray data from the Fermi satellite. This has been interpreted as evidence for a population of hidden cosmic-ray accelerators. We propose an alternative explanation of this conundrum on the basis of cold dark matter which decays into sterile neutrinos that after oscillations produce the bump in the cosmic neutrino spectrum.