Neutrino Flux Research Articles

Floor of Cosmogenic Neutrino Fluxes above 1017 eV

The search for neutrinos with energies greater than 1017 eV is being actively pursued. Although normalization of the dominant neutrino flux is highly uncertain, a floor level is guaranteed by the interactions of extragalactic cosmic rays with milky Way gas. We estimate that this floor level gives an energy flux of E2ϕν≃10−13−0.5+0.5GeVcm−2sr−1s−1 at 1018 eV, where uncertainties arise from the modeling of the gas distribution and the experimental determination of the mass composition of ultra–high-energy cosmic rays on Earth. Based on a minimal model of cosmic-ray production to explain the mass-discriminated energy spectra observed on Earth above 5 × 1018 eV, we also present generic estimates of the neutrino fluxes expected from extragalactic production that generally exceed the aforementioned guaranteed floor. The prospects for detecting neutrinos above 1018 eV remain challenging, however, unless proton acceleration to the highest energies is at play in a subdominant population of cosmic-ray sources or new physical phenomena are at work.

Resonant spin-flavor precession of sterile neutrinos

We analyze the impact of resonant conversions mediated by non-vanishing magnetic moments between active neutrinos and a heavy sterile neutrino on the supernova neutrino flux. We present the level-crossing scheme for such a scenario and derive the neutrino fluxes after conversion, paying particular attention to the order in which the resonances occur. We then compute the expected event rates from the neutronization burst of a future supernova at DUNE and Hyper-Kamiokande to derive new constraints on the neutrino magnetic moment. With this, we find a sensitivity down to a few 10-15 μB for a sterile neutrino in the O(eV) mass range.

All-sky Search for Transient Astrophysical Neutrino Emission with 10 Years of IceCube Cascade Events

Neutrino flares in the sky are searched for in data collected by IceCube between 2011 and 2021 May. This data set contains cascade-like events originating from charged-current electron neutrino and tau neutrino interactions and all-flavor neutral-current interactions. IceCube’s previous all-sky searches for neutrino flares used data sets consisting of track-like events originating from charged-current muon neutrino interactions. The cascade data set is statistically independent of the track data sets, and while inferior in angular resolution, the low-background nature makes it competitive and complementary to previous searches. No statistically significant flare of neutrino emission was observed in an all-sky scan. Upper limits are calculated on neutrino flares of varying duration from 1 hr to 100 days. Furthermore, constraints on the contribution of these flares to the diffuse astrophysical neutrino flux are presented, showing that multiple unresolved transient sources may contribute to the diffuse astrophysical neutrino flux.

Contribution of Neutrino-dominated Accretion Flows to the Cosmic MeV Neutrino Background

Neutrino-dominated accretion flows (NDAFs) are one of the important MeV neutrino sources and significantly contribute to the cosmic diffuse neutrino background. In this paper, we investigate the spectrum of the diffuse NDAF neutrino background (DNNB) by fully considering the effects of the progenitor properties and initial explosion energies based on core-collapse supernova (CCSN) simulations, and estimate the detectable event rate by the Super-Kamiokande detector. We find that the predicted background neutrino flux is mainly determined by the typical CCSN initial explosion energy and progenitor metallicity. For the optimistic cases, in which the typical initial explosion energy is low, the diffuse flux of the DNNB is comparable to the diffuse supernova neutrino background, which might be detected by upcoming larger neutrino detectors, such as Hyper-Kamiokande, the Jiangmen Underground Neutrino Observatory, and the Deep Underground Neutrino Experiment. Moreover, the strong outflows from NDAFs could dramatically decrease their contribution to the neutrino background.

Neutron stars in accreting systems -- Signatures of the QCD phase transition

Neutron stars (NS) that are born in binary systems with a main-sequence star companion can experience mass transfer, resulting in the accumulation of material at the surface of the NS. This, in turn, leads to the continuous growth of the NS mass and the associated steepening of the gravitational potential. Supposing the central density surpasses the onset for the phase transition from nuclear, generally hadronic matter to deconfined quark-gluon plasma, which is a quantity currently constrained solely from an upper limit by asymptotic freedom in quantum chromodynamics (QCD), the system may experience a dynamic response due to the appearance of additional degrees of freedom in the equation of state (EOS). This dynamical response might give rise to a rapid softening of the EOS during the transition in the hadron-quark matter co-existence region. While this phenomenon has long been studied in the context of hydrostatic configurations, the dynamical implications of this problem are still incompletely understood. It is the purpose of the present paper to simulate the dynamics of NSs with previously accreted envelopes caused by the presence of a first-order QCD phase transition. Therefore, we employed the neutrino radiation hydrodynamics treatment based on the fully general relativistic approach in spherical symmetry, implementing a three-flavor Boltzmann neutrino transport and a microscopic model EOS that contains a first-order hadron-quark phase transition. The associated neutrino signal shows a sudden rise in the neutrino fluxes and average energies, becoming observable for the present generation of neutrino detectors for a galactic event, and a gravitational wave mode analysis revealed the behaviors of the dominant $f$ mode and the first and the second gravity $g$ modes that are excited during the NS evolution across the QCD phase transition.

Constraints on the Origins of the Galactic Neutrino Flux Detected by IceCube

Galactic and extragalactic objects in the Universe are sources of high-energy neutrinos that may contribute to the astrophysical neutrino signal seen by IceCube. Recently, a study done using cascade-like events seen by IceCube reported neutrino emission from the Galactic plane with >4σ significance. In this work, we put a lower limit on the number of Galactic sources required to explain this emission. To achieve this, we use a simulation package created to simulate point sources in the Galaxy along with the neutrino and gamma-ray flux emissions originating from them. Along with using past IceCube discovery potential curves, we also account for Eddington bias effects due to Poisson fluctuations in the number of detected neutrino events. We present a toy Monte Carlo simulation to show that there must be at least eight sources, each with luminosity less than 1.6 × 1035 erg s−1, responsible for the Galactic neutrino emission. Our results constrain the number of individual point-like emission regions, which apply both to discrete astrophysical sources and to individual points of diffuse emission.

Detecting neutrinos from supernova bursts in PandaX-4T* *This project is Supported in part by the National Natural Science Foundation of China (12090060, 12090063, 12105052, 12005131, 11905128, 11925502), and the Office of Science and Technology, Shanghai Municipal Government, China (22JC1410100)

Neutrinos from core-collapse supernovae are essential for understanding neutrino physics and stellar evolution. Dual-phase xenon dark matter detectors can be used to track explosions of galactic supernovae by detecting neutrinos through coherent elastic neutrino-nucleus scatterings. In this study, a variation of progenitor masses and explosion models are assumed to predict neutrino fluxes and spectra, which result in the number of expected neutrino events ranging from 6.6 to 13.7 at a distance of 10 kpc over a 10-s duration with negligible backgrounds at PandaX-4T. Two specialized triggering alarms for monitoring supernova burst neutrinos are built. The efficiency of detecting supernova explosions at various distances in the Milky Way is estimated. These alarms will be implemented in the real-time supernova monitoring system at PandaX-4T in the near future, which will provide supernova early warnings for the astronomical community.

Proto-neutron star convection and the neutrino-driven wind: implications for the νp-process

ABSTRACT Recent studies of the neutrino-driven wind from proto-neutron stars have indicated that the wind is likely proton rich for much of its lifetime, and the high flux of neutrinos can induce νp-process nucleosynthesis allowing for the formation of heavy elements. It has also been shown that gravito-acoustic waves, generated by convection within the proto-neutron star, can significantly alter the dynamics and nucleosynthesis in the wind. Therefore, we present a study of the effects of convection-driven waves on the nucleosynthesis in proton-rich neutrino-driven winds, focusing on the νp-process. We find that wave effects can strongly impact νp-process nucleosynthesis even at wave luminosities a factor of 10−5 smaller than the total neutrino luminosity. The momentum flux of the waves accelerates the wind, reducing the net neutrino heating and the persistent neutron abundance created by p($\bar{\nu }_\mathrm{ e},e^+$), which impedes νp-process nucleosynthesis. However, this effect is generally counteracted by the effects of waves on seed nucleus formation, as the acceleration of the wind and the heating that occurs as these waves shock both favour a more α-rich environment with very little heavy seed nucleus formation. Overall, higher wave luminosities correlate (albeit non-monotonically) with heavier element νp-processing, up to A ≈ 200 in some cases. At very high wave luminosities (≳10−3Lν), early shock heating by the waves disrupts α recombination, and drives a suppressed, fast-outflow r-process proceeding up to A ≈ 200. This occurs despite an assumed neutrino spectrum that predicts a proton-rich wind with equilibrium Ye = 0.6.

Observation of Seven Astrophysical Tau Neutrino Candidates with IceCube.

We report on a measurement of astrophysical tau neutrinos with 9.7yr of IceCube data. Using convolutional neural networks trained on images derived from simulated events, seven candidate ν_{τ} events were found with visible energies ranging from roughly 20TeV to 1PeV and a median expected parent ν_{τ} energy of about 200TeV. Considering backgrounds from astrophysical and atmospheric neutrinos, and muons from π^{±}/K^{±} decays in atmospheric air showers, we obtain a total estimated background of about 0.5 events, dominated by non-ν_{τ} astrophysical neutrinos. Thus, we rule out the absence of astrophysical ν_{τ} at the 5σ level. The measured astrophysical ν_{τ} flux is consistent with expectations based on previously published IceCube astrophysical neutrino flux measurements and neutrino oscillations.

New constraints on the gamma-ray and high energy neutrino fluxes from the circumstellar interaction of SN 2023ixf

The recent supernova, SN 2023ixf, one of the closest observed type II SNe has revealed the presence of a dense circumstellar material (CSM). Interaction of the SN ejecta with this dense CSM might create high energy protons of PeV energies through shock acceleration. These accelerated protons then colliding with the CSM (inelastic pp collision) can produce secondaries such as high energy gamma-rays and neutrinos. However, no gamma-rays and neutrinos have been detected by Fermi-LAT and IceCube from this event. Fermi-LAT has placed an upper limit on the gamma-ray flux above 100 MeV to be 2.6 × 10-11 erg cm-2 s-1. On the other hand, IceCube's upper limit on muon neutrino flux is 7.3 × 10-2 GeV cm-2. Taking these limits into account and using the shock-CSM properties derived from multi-wavelength observations, we obtain new upper limits on the gamma-ray (10-11 erg cm-2 s-1) and neutrino (10-3 GeV cm-2) fluxes from SN 2023ixf produced via the pp interaction channel. While we found the gamma-ray flux to be consistent with Fermi-LAT's upper limit, the neutrino flux is found to be about 2 orders of magnitude smaller than the IceCube's upper limit. We further analyse the detection prospects of such secondary signals from future SN 2023 like events with upcoming detectors, CTA and IceCube-Gen2 and found to have great discovery potential, if any similar event occurs within 7 Mpc.

Searches for neutrino counterparts of gravitational waves from the LIGO/Virgo third observing run with KM3NeT

The KM3NeT neutrino telescope is currently being deployed at two different sites in the Mediterranean Sea. First searches for astrophysical neutrinos have been performed using data taken with the partial detector configuration already in operation. The paper presents the results of two independent searches for neutrinos from compact binary mergers detected during the third observing run of the LIGO and Virgo gravitational wave interferometers. The first search looks for a global increase in the detector counting rates that could be associated with inverse beta decay events generated by MeV-scale electron anti-neutrinos. The second one focuses on upgoing track-like events mainly induced by muon (anti-)neutrinos in the GeV–TeV energy range. Both searches yield no significant excess for the sources in the gravitational wave catalogs. For each source, upper limits on the neutrino flux and on the total energy emitted in neutrinos in the respective energy ranges have been set. Stacking analyses of binary black hole mergers and neutron star-black hole mergers have also been performed to constrain the characteristic neutrino emission from these categories.

A stacked search for spatial coincidences between IceCube neutrinos and radio pulsars

We carry out a stacked search for spatial coincidences between all the known radio pulsars and TeV neutrinos from the IceCube 10 year (2008–2018) muon track data, as a followup to our previous work on searching for spatial coincidences with individual pulsars. We consider three different weighting schemes to stack the contributions from each pulsar. We do not find a statistically significant excess using this method. We report the 95% c.l. neutrino flux upper limit as a function of the neutrino energy. We have also made our analysis codes publicly available.

Model-independent Approach of the JUNO 8B Solar Neutrino Program

The physics potential of detecting 8B solar neutrinos will be exploited at the Jiangmen Underground Neutrino Observatory (JUNO), in a model-independent manner by using three distinct channels of the charged current (CC), neutral current (NC), and elastic scattering (ES) interactions. Due to the largest-ever mass of 13C nuclei in the liquid scintillator detectors and the expected low background level, 8B solar neutrinos are observable in the CC and NC interactions on 13C for the first time. By virtue of optimized event selections and muon veto strategies, backgrounds from the accidental coincidence, muon-induced isotopes, and external backgrounds can be greatly suppressed. Excellent signal-to-background ratios can be achieved in the CC, NC, and ES channels to guarantee the observation of the 8B solar neutrinos. From the sensitivity studies performed in this work, we show that JUNO, with 10 yr of data, can reach the 1σ precision levels of 5%, 8%, and 20% for the 8B neutrino flux, sin2θ12 , and Δm212 , respectively. Probing the details of both solar physics and neutrino physics would be unique and helpful. In addition, when combined with the Sudbury Neutrino Observatory measurement, the world's best precision of 3% is expected for the measurement of the 8B neutrino flux.

Sibyll[formula omitted]

In the last decade, an increasing number of datasets have revealed a consistent discrepancy between the number of muons measured in ultra-high-energy extensive air showers (EAS) and the numbers predicted by simulations. This gap persists despite incorporating Large Hadron Collider (LHC) data into the tuning of current hadronic interaction models, leading to the phenomenon often termed the “muon puzzle”. To gain a deeper understanding of the potential origins of this muon puzzle, we have developed Sibyll★, a series of phenomenologically modified versions of Sibyll 2.3d. In these models, we have increased muon production by altering ρ0, baryon–antibaryon pair, or kaon production in hadronic multiparticle production processes. These variants remain within bounds from provided by accelerator measurements, including those from the LHC and fixed-target experiments, notably NA49 and NA61, showing a level of consistency comparable to Sibyll 2.3d. Our findings show that these modifications can increase the muon count in EAS by up to 35%, while minimally affecting the depth of shower maximum (Xmax) and other shower variables. Additionally, we assess the impact of these modifications on various observables, including inclusive muon and neutrino fluxes and the multiplicities of muon bundles in deep underground and water/ice Cherenkov detectors. We aim for at least one of these model variants to offer a more accurate representation of EAS data at the highest energies, thereby enhancing the quality of Monte Carlo predictions used in training neural networks. This improvement is crucial for achieving more reliable data analyses and interpretations.

High-Energy and Ultra-High-Energy Neutrino Astrophysics

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.

Tidal disruption events and dark matter scatterings with neutrinos and photons

Stars can be tidally disrupted when passing near a black hole, and the debris can induce a flux of high-energy neutrinos. It has been discussed that there are hints in IceCube data of high-energy neutrinos produced in Tidal Disruption Events. The emitting region of neutrinos and photons in these astrophysical events is likely to be located in the vicinity of the central black hole, where the dark matter density might be significantly larger than in the outer regions of the galaxy. We explore the potential attenuation of the emitted neutrino and photon fluxes due to interactions with dark matter particles around the supermassive black hole of the host galaxies of AT2019dsg, AT2019fdr and AT2019aalc, and study the implications for some well-motivated models of dark matter-neutrino and dark matter-photon interactions. Furthermore, we discuss the complementarity of our constraints with values of the dark matter-neutrino scattering cross section proven to alleviate some cosmological tensions.

Energy-dependent flavour ratios in neutrino telescopes from charm

The origin of the observed diffuse neutrino flux is not yet known. Studies of the relative flavour content of the neutrino flux detected at Earth can give information on the production mechanisms at the sources and on flavour mixing, complementary to measurements of the spectral index and normalization. Here we demonstrate the effects of neutrino fluxes with different spectral shapes and different initial flavour compositions dominating at different energies, and we study the sensitivity of future measurements with the IceCube Neutrino Observatory. Where one kind of flux gives way to another, this shows up as a non-trivial energy dependence in the flavour compositions. We explore this in the context of slow-jet supernovae and magnetar-driven supernovae — two examples of astrophysical sources where charm production may be effective. Using current best-fit neutrino mixing parameters and the projected 2040 IceCube uncertainties, we use event ratios of different event morphologies at IceCube to illustrate the possibilities of distinguishing the energy dependence of neutrino flavour ratios.

Searches for Neutrinos in the Direction of Radio-bright Blazars with the ANTARES Telescope

Active galaxies, especially blazars, are among the most promising extragalactic candidates for high-energy neutrino sources. To date, ANTARES searches included these objects and used GeV–TeV γ-ray flux to select blazars. Here, a statistically complete blazar sample selected by their bright radio emission is used as the target for searches of origins of neutrinos collected by the ANTARES neutrino telescope over 13 yr of operation. The hypothesis of a neutrino–blazar directional correlation is tested by pair counting and a complementary likelihood-based approach. The resulting posttrial p-value is 3.0% (2.2σ in the two-sided convention). Additionally, a time-dependent analysis is performed to search for temporal clustering of neutrino candidates as a means of detecting neutrino flares in blazars. None of the investigated sources alone reaches a significant flare detection level. However, the presence of 18 sources with a pretrial significance above 3σ indicates a p = 1.4% (2.5σ in the two-sided convention) detection of a time-variable neutrino flux. An a posteriori investigation reveals an intriguing temporal coincidence of neutrino, radio, and γ-ray flares of the J0242+1101 blazar at a p = 0.5% (2.9σ in the two-sided convention) level. Altogether, the results presented here suggest a possible connection of neutrino candidates detected by the ANTARES telescope with radio-bright blazars.

Phenomenology of superheavy decaying dark matter from string theory

We study the phenomenology of superheavy decaying dark matter with mass around 1010 GeV which can arise in the low-energy limit of string compactifications. Generic features of string theory setups (such as high scale supersymmetry breaking and epochs of early matter domination driven by string moduli) can accommodate superheavy dark matter with the correct relic abundance. In addition, stringy instantons induce tiny R-parity violating couplings which make dark matter unstable with a lifetime well above the age of the Universe. Adopting a model-independent approach, we compute the flux and spectrum of high-energy gamma rays and neutrinos from three-body decays of superheavy dark matter and constrain its mass-lifetime plane with current observations and future experiments. We show that these bounds have only a mild dependence on the exact nature of neutralino dark matter and its decay channels. Applying these constraints to an explicit string model sets an upper bound of O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O} $$\\end{document}(0.1) on the string coupling, ensuring that the effective field theory is in the perturbative regime.

Neutrino production in starburst galaxies

ABSTRACT Understanding the origin of the diffuse flux of high-energy astrophysical neutrinos detected by IceCube has become a challenging issue within present High Energy Astrophysics. In this work, we present a model to explore the potential neutrino emission of starburst galaxies (SBG) by considering three different neutrino production zones that can be associated to a typical single SBG. The first zone is the starburst nucleus, where due to the high rate of supernova explosions, a significant amount of protons can be accelerated to high energies and undergo pp interactions with cold protons of the interstellar medium. The second zone we consider is the corresponding to the starburst wind, which is formed by the hot gas that emerges from the nucleus and interacts with the intergalactic medium generating shocks. Protons accelerated there can undergo pp interactions with the ambient matter. The third neutrino production zone we consider, is an external one, where we account for the possibility that protons escaping from the whole system interact with the cosmic microwave background. Finally, adding the neutrino contributions of the three zones, we calculate the diffuse neutrino flux and the diffuse photon flux by integration on the redshift range appropriate for SBG. We find that the model behaves well applied to nearby galaxies such as M82 and NGC 253. The contributions made to the diffuse neutrino flux are able to explain part of the data provided by IceCube if typical parameters are considered.