Cosmogenic Neutrinos Research Articles

Modified Temperature–Redshift Relation and Ultra-high-energy Cosmic Ray Propagation

We reexamine the interactions of ultra-high-energy cosmic rays (UHECRs) with photons from the cosmic microwave background (CMB) under a changed, locally nonlinear temperature–redshift relation T(z). This changed temperature–redshift relation has recently been suggested by the postulate of subjecting thermalized and isotropic photon gases such as the CMB to an SU(2) rather than a U(1) gauge group. This modification of ΛCDM is called SU(2)CMB, and some cosmological parameters obtained by SU(2)CMB seem to be in better agreement with local measurements of the same quantities, in particular H 0 and S8. In this work, we apply the reduced CMB photon density under SU(2)CMB to the propagation of UHECRs. This leads to a higher UHECR flux just below the ankle in the cosmic ray spectrum and slightly more cosmogenic neutrinos under otherwise equal conditions for emission and propagation. Most prominently, the proton flux is significantly increased below the ankle (5 × 1018 eV) for hard injection spectra and without considering the effects of magnetic fields. The reduction in CMB photon density also favors a decreased cosmic ray source evolution than the best fit using ΛCDM. In consequence, it seems that SU(2)CMB favors sources that evolve like the star formation rate, such as starburst galaxies and gamma-ray bursts, over active galactic nuclei as origins of UHECRs. We conclude that the question about the nature of primary sources of UHECRs is directly affected by the assumed temperature–redshift relation of the CMB.

Constraints on the proton fraction of cosmic rays at the highest energies and the consequences for cosmogenic neutrinos and photons

Over the last decade, observations have shown that the mean mass of ultra-high-energy cosmic rays (UHECRs) increases progressively toward the highest energies. However, the precise composition is still unknown and several theoretical studies hint at the existence of a subdominant proton component up to the highest energies. Motivated by the exciting prospect of performing charged-particle astronomy with ultra-high-energy (UHE) protons we quantify the level of UHE-proton flux that is compatible with present multimessenger observations and the associated fluxes of neutral messengers produced in the interactions of the protons. We study this scenario with numerical simulations of two independent populations of extragalactic sources and perform a fit to the combined UHECR energy spectrum and composition observables, constrained by diffuse gamma-ray and neutrino observations. We find that up to of order 10% of the cosmic rays at the highest energies can be UHE protons, although the result depends critically on the selected hadronic interaction model for the air showers. Depending on the maximum proton energy (E max p) and the redshift evolution of sources, the associated flux of cosmogenic neutrinos and UHE gamma rays can significantly exceed the multimessenger signal of the mixed-mass cosmic rays. Moreover, if E max p is above the GZK limit, we predict a large flux of UHE neutrinos above EeV energies that is absent in alternate scenarios for the origin of UHECRs. We present the implications and opportunities afforded by these UHE proton, neutrino and photon fluxes for future multimessenger observations.

Muon energy reconstruction for applications in neutrino astronomy in the DUNE far detector

DUNE (Deep Underground Neutrino Experiment) is a proposed long-baseline neutrino oscillation experiment located in the United States. The main physics objectives of DUNE are to measure neutrino oscillations and interactions, search for nucleon decay, observe supernova neutrino bursts and beyond Standard Model (BSM) effects. The DUNE far detector will be located 4850 feet underground at the Sanford Underground Research Facility in Lead, South Dakota. It will house the world's largest liquid-argon time projection chambers (TPC). The DUNE far detector can detect high-energy leptons that arise from interactions of cosmogenic neutrinos and search for neutrinos originating from the decay of weakly-interactive massive particles (WIMPs) annihilations occurring inside the Sun. Selecting upward-going muons reduces the background from cosmic-ray muons. The muon energy is estimated from the electromagnetic showers accompanying the muon, a technique that allows energy reconstruction up to a few hundred TeV.

IceCube and the origin of ANITA-IV events

Recently, the ANITA collaboration announced the detection of new, unsettling upgoing Ultra-High-Energy (UHE) events. Understanding their origin is pressing to ensure success of the incoming UHE neutrino program. In this work, we study their internal consistency and the implications of the lack of similar events in IceCube. We introduce a generic, simple parametrization to study the compatibility between these two observatories in Standard Model-like and Beyond Standard Model scenarios: an incoming flux of particles that interact with Earth nucleons with cross section σ, producing particle showers along with long-lived particles that decay with lifetime τ and generate a shower that explains ANITA observations. We find that the ANITA angular distribution imposes significant constraints, and when including null observations from IceCube only τ ~ 10−3–10−2 s and σ ~ 10−33– 10−32 cm2 can explain the data. This hypothesis is testable with future IceCube data. Finally, we discuss a specific model that can realize this scenario. Our analysis highlights the importance of simultaneous observations by high-energy optical neutrino telescopes and new UHE radio detectors to uncover cosmogenic neutrinos or discover new physics.

Probing heavy sterile neutrinos at neutrino telescopes via the dipole portal

The question of how heavy a sterile neutrino can be probed in experiments leads us to investigate the Primakoff production of heavy sterile neutrinos from ultrahigh-energy neutrinos via the magnetic dipole portal. Despite the suppression from the small magnetic moment, the transition is significantly enhanced by tiny t-channel momentum transfers, similar to the resonant production of pions and axions in an external electromagnetic field. Based on the current IceCube measurement of astrophysical neutrinos up to PeV energies, strong constraints can already be derived on the transition magnetic moments of sterile neutrinos up to TeV masses. Moreover, we investigate the sensitivity of future tau neutrino telescopes, which are designed for EeV cosmogenic neutrino detection. We find that sterile neutrino masses as large as 30TeV can be probed at tau neutrino telescopes such as GRAND, POEMMA, and Trinity.

High-energy Neutrino Emission from Espresso-reaccelerated Ions in Jets of Active Galactic Nuclei

We present a bottom-up calculation of the flux of ultrahigh-energy cosmic rays (UHECRs) and high-energy neutrinos produced by powerful jets of active galactic nuclei (AGNs). By propagating test particles in 3D relativistic magnetohydrodynamic jet simulations, including a Monte Carlo treatment of sub-grid pitch-angle scattering and attenuation losses due to realistic photon fields, we study the spectrum and composition of the accelerated UHECRs and estimate the amount of neutrinos produced in such sources. We find that UHECRs may not be significantly affected by photodisintegration in AGN jets where the espresso mechanism efficiently accelerates particles, consistent with Auger’s results that favor a heavy composition at the highest energies. Moreover, we present estimates and upper bounds for the flux of high-energy neutrinos expected from AGN jets. In particular, we find that (i) source neutrinos may account for a sizable fraction, or even dominate, the expected flux of cosmogenic neutrinos; (ii) neutrinos from the β-decay of secondary neutrons produced in nucleus photodisintegration end up in the teraelectronvolt to petaelectronvolt band observed by IceCube, but can hardly account for the observed flux; (iii) UHECRs accelerated via the espresso mechanism lead to nearly isotropic neutrino emission, which suggests that nearby radio galaxies may be more promising as potential sources. We discuss our results in light of multimessenger astronomy and current/future neutrino experiments.

Modeling Neutrino and Background Signals for the Payload for Ultrahigh Energy Observations (PUEO) Experiment

In the current age of multi-messenger astrophysics, Very High Energy (VHE) cosmic neutrinos (E > 1 PeV) represent a unique observation window into the most extreme astrophysical events in the universe. Measurements of the neutrino flux in this high energy regime provide information regarding the distribution and composition of Ultra-High Energy Cosmic Rays (UHECR), details of source acceleration mechanics, and definitive tests of physics beyond the standard model. Observations in multiple different detection channels (e.g. optical, radio, direct particle counting) are being explored to extend the sensitivity to neutrinos above PeV energies. The Payload for Ultrahigh Energy Observations (PUEO) is a long duration balloon experiment that builds on the successes of the Antarctic Impulsive Transient Antenna (ANITA) experiment to probe the cosmic neutrino flux above EeV energies. PUEO, like ANITA, seeks to measure coherent radio emission in the form of Askaryan emission from in-ice neutrino interactions and both geomagnetic and Askaryan emission from Extensive Air Showers (EAS) produced by the decays of Earth-emergent τ-leptons sourced from τ neutrinos. To evaluate the sensitivity of PUEO (and other detectors) to a given flux of neutrinos, it is necessary to accurately model i) the propagation of neutrinos through the Earth ii) the emission generated from the neutrino-sourced particle shower iii) the detector performance to a generated signal and iv) relevant backgrounds. Numerous software frameworks exist to model these different mechanisms independently, but often require significant work to use together. ν SpaceSim is an open source, end-to-end neutrino simulation package that models these described mechanisms for an arbitrary detector geometry in both the optical and radio emission channels. For a given experimental design,ν SpaceSim is designed to model the sensitivity to both the cosmogenic neutrino flux and to astrophysical neutrino transient events. The highly modular design of ν SpaceSim allows for comparison and exploration of different physics models within the same code base. In this contribution, we detail the state of the ν SpaceSim code as it pertains to modeling the sensitivity of the PUEO experiment, and highlight the mechanisms necessary to perform this calculation. We also describe the near-term improvements to the radio emission calculation in ν SpaceSim and the modeling of the most relevant backgrounds for PUEO: the direct (above-the-limb) cosmic rays, and the indirect (ice-reflected) cosmic ray signals.

Double and multiple bangs at tau neutrino telescopes

In light of the exciting campaign of cosmogenic neutrino detection, we investigate the double and multiple tau bangs detectable at future tau neutrino telescopes. Such events are expected from the Standard Model (SM) higher-order processes, which can be easily identified with broad techniques anticipated at future tau neutrino telescopes. We find that SM perturbative processes can already contribute observable double-bang events to telescopes with a sensitivity of collecting {mathcal {O}}(100) cosmogenic neutrino events. The detectable but suppressed rate in fact makes the double and multiple bangs an excellent probe of SM unknowns and possible new physics beyond. As a case study, the nonperturbative sphaleron process, which can copiously produce multiple tau bangs, is explored.

Implications of multiwavelength spectrum on cosmic-ray acceleration in blazar TXS 0506+056

Context.The MAGIC collaboration has recently analyzed data from a long-term multiwavelength campaign of theγ-ray blazar TXS 0506+056. In December 2018 it was flaring in the very high-energy (VHE;E > 100 GeV)γ-ray band, but no simultaneous neutrino event was detected.Aims.We modeled the observed spectral energy distribution (SED) using a one-zone leptohadronic emission.Methods.We estimated the neutrino flux through the restriction from the observed X-ray flux on the secondary radiation due to the hadronic cascade, initiated by protons with energyEp ≲ 0.1 EeV. We assumed that ultra-high-energy cosmic rays (UHECRs;E ≳ 0.1 EeV), with the same slope and normalization as the low-energy spectrum, are accelerated in the jet but escape efficiently. We propagate the UHE protons in a random turbulent extragalactic magnetic field (EGMF).Results.The leptonic emission from the jet dominates the GeV range, whereas the cascade emission from CR interactions in the jet contributes substantially to the X-ray and VHE range. The line-of-sight cosmogenicγ-rays from UHECRs produce a hardening in the VHE spectrum. Our model prediction for neutrinos from the jet is consistent with the 7.5-year flux limit by IceCube and shows no variability during the MAGIC campaign. Therefore, we infer that the correlation between GeV-TeVγ-rays and neutrino flare is minimal. The luminosity in CRs limits the cosmogenicγ-ray flux, which in turn bounds the RMS value of the EGMF to ≳10−5nG. The cosmogenic neutrino flux is lower than the IceCube-Gen2 detection potential for 10 yr of observation.Conclusions.Very high-energyγ-ray variability should arise from increased activity inside the jet; thus, detecting steady flux at multi-TeV energies may indicate UHECR acceleration. Upcomingγ-ray imaging telescopes, such as the CTA, will be able to constrain the cosmogenicγ-ray component in the SED of TXS 0506+056.

EUSO-SPB2 Fluorescence Telescope trigger test within the EUSO@TurLab Project

The second generation Extreme Universe Space Observatory on a Super-Pressure Balloon (EUSO-SPB2) mission is on track to be approved by NASA for a long duration flight (up to 100 days) in 2023 from Wanaka, New Zealand. EUSO-SPB2 will monitor the night atmosphere of the Southern hemisphere from 33 km altitude to detect Ultra-High Energy Cosmic Rays (UHECRs) and search for astrophysical and cosmogenic neutrinos. EUSO-SPB2 features two telescopes, a Cherenkov (CT) and a Fluorescence (FT) Telescope. The hardware implementation and performance of the FT trigger logic were tested at the TurLab facility, hosted at the University of Turin. The tests proved the correct hardware implementation of the trigger logic and its ability to detect μs timescale transient signals.

The Giant Radio Array for Neutrino Detection (GRAND) Project

GRAND is designed to detect ultra-high-energy cosmic particles – specially neutrinos, cosmic rays and gamma rays using radio antennas. With ~20 mountainous sites around the world it will cover a total area of 200,000 km^{2}2. The planned sensitivity of 10^{-10}−10 GeV cm^{-2}−2 s^{-1}−1 sr^{-1}−1 above 5\times10^{17}5×1017 eV will likely ensure the detection of cosmogenic neutrinos predicted by most common scenarios enabling neutrino astronomy. Furthermore, PeV–EeV neutrinos can test particle interactions at energies above those achieved in accelerators. The pathfinder stage GRANDProto300 is planned to start taking data in 2021. We present the current overall status of the project with emphasis on the neutrino physics.

A new probe of relic neutrino clustering using cosmogenic neutrinos

We propose a new probe of cosmic relic neutrinos (CνB) using their resonant scattering against cosmogenic neutrinos. Depending on the lightest neutrino mass and the energy spectrum of the cosmogenic neutrino flux, a Standard Model vector meson (such as a hadronic ρ) resonance can be produced via νν¯ annihilation. This leads to a distinct absorption feature in the cosmogenic neutrino flux at an energy solely determined by the meson mass and the neutrino mass, apart from redshift. By numerical coincidence, the position of the ρ-resonance overlaps with the originally predicted peak of the Greisen-Zatsepin-Kuzmin (GZK) neutrino flux, which offers an enhanced effect at higher redshifts. We show that this absorption feature in the GZK neutrino flux may be observable in future radio-based neutrino observatories, such as IceCube-Gen2 radio, provided there exists a large overdensity in the CνB distribution. This therefore provides a new probe of CνB clustering at large redshifts, complementary to the laboratory probes (such as KATRIN) at zero redshift.

Tau Appearance from High-Energy Neutrino Interactions.

High-energy muon and electron neutrinos yield a non-negligible flux of tau neutrinos as they propagate through Earth. In this Letter, we address the impact of this additional component in the PeV and EeV energy regimes for the first time. Above 300TeV, this contribution is predicted to be significantly larger than the atmospheric background, and it alters current and future neutrino telescopes' capabilities to discover a cosmic tau-neutrino flux. Further, we demonstrate that Earth-skimming neutrino experiments, designed to observe tau neutrinos, will be sensitive to cosmogenic neutrinos even in extreme scenarios without a primary tau-neutrino component.

Cosmogenic gamma-ray and neutrino fluxes from blazars associated with IceCube events

Context.Blazars constitute the vast majority of extragalacticγ-ray sources. They can also contribute a sizable fraction of the diffuse astrophysical neutrinos detected by IceCube. In the past few years, the real-time alert system of IceCube has led to the multiwavelength follow-up of very high-energy neutrino events of plausible astrophysical origin. Spatial and temporal coincidences of a number of these neutrino events withγ-ray blazars provide a unique opportunity to decipher cosmic-ray interactions in the relativistic jets.Aims.The aim of this work is to test if theγ-ray blazars associated with the IceCube neutrino events are also sources of ultra-high-energy cosmic rays (UHECRs;E > 1018eV).Methods.Assuming that blazars accelerate UHECRs, we calculate the “guaranteed” contribution to the line-of-sight cosmogenicγ-ray and neutrino fluxes from four blazars associated with IceCube neutrino events. We compare these fluxes with the sensitivities of the upcomingγ-ray imaging telescopes, such as the CTA, and with the planned neutrino detectors, such as IceCube-Gen2.Results.We find that detection of the cosmogenic neutrino fluxes from the blazars TXS 0506+056, PKS 1502+106, and GB6 J1040+0617 would require UHECR luminosity ≳10 times the inferred neutrino luminosity from the associated IceCube events, with the maximum UHECR proton energyEp, max ≈ 1020eV. Cosmogenicγ-ray emission from blazars TXS 0506+056, 3HSP J095507.9 +355101, and GB6 J1040+0617 can be detected by the CTA if the UHECR luminosity is ≳10 times the neutrino luminosity inferred from the associated IceCube events and forEp, max ≳ 1019eV.Conclusions.Detection of cosmogenic neutrino and/orγ-ray flux(es) from blazars associated with IceCube neutrinos may lead to the first direct signature(s) of UHECR sources. Given their relatively low redshifts and hence total energetics, TXS 0506+056 and 3HSP J095507.9+355101 should be the prime targets for upcoming large neutrino andγ-ray telescopes.

Comparative study of Dirac and Majorana ultrahigh-energy neutrino oscillations in an interstellar magnetic field

We examine the ultrahigh-energy neutrino propagation in interstellar space in the Dirac and Majorana cases. Employing the two-neutrino mixing approximation and using the astrophysical constraints on neutrino magnetic moments, we show that both the flavor and the spin oscillations of the Dirac and Majorana neutrinos exhibit qualitatively different behaviors in an interstellar magnetic field for neutrino-energy values characteristic of, respectively, the cosmogenic neutrinos and well above the Greisen-Zatsepin-Kuz’min cutoff.

Newly Born Extragalactic Millisecond Pulsars as Efficient Emitters of PeV Neutrinos

The origins of the diffuse flux of cosmogenic PeV neutrinos detected in the IceCube experiment during 2010 - 2017 remain unidentified. A population of extragalactic newly born fast spinning pulsars are investigated as possible candidates for generating the PeV energy scale neutrinos. A two-step mechanism of particle acceleration is adopted for transferring energy from star rotation to high energy electrons. Electrons might be boosted up to $\approx 0.01$ EeV energies and above, and produce ultra-high-energy (UHE) neutrinos and gamma rays when these electrons interact with low energy positrons and soft radiations in the acceleration zone. The theoretically derived extragalactic diffuse muon neutrino flux in the energy range [1-10] PeV is found consistent with the IceCube level if only a fraction ($\eta_{k} \approx 0.31\%$) of the total bolometric luminosity of pulsars are transferred to power the PeV neutrinos. Using the above value of the cosmic ray electron loading parameter $\eta_{k}$, the diffuse gamma ray flux from inverse Compton scattering off UHE electrons in the soft radiation field might be predicted from the model.

Correlated single- and few-electron backgrounds milliseconds after interactions in dual-phase liquid xenon time projection chambers

We characterize single- and few-electron backgrounds that are observed in dual-phase liquid xenon time projection chambers at timescales greatly exceeding a maximum drift time after an interaction. These instrumental backgrounds limit a detector's sensitivity to dark matter and cosmogenic neutrinos. Using the ∼ 150 g liquid xenon detector at Purdue University, we investigate how these backgrounds, produced after 122 keV 57Co Compton interactions, behave under different detector conditions. We find that the rates of single- and few-electron signals follow power-laws with time after the interaction. We observe linearly increasing rates with increased extraction field. The relationship of the rates in the single-electron background with increased drift field is unclear. Normalizing the rates to the primary interaction's measured ionization signal, the rates increase linearly with the depth of the interaction. We test the hypothesis that infrared photons (1550 nm) would stimulate and accelerate electron emission via photodetachment from impurities, but find that even 1 Watt of infrared light fails to reduce these backgrounds. We thus provide a characterization that can inform background models for low-energy rare event searches.

Active Galactic Nuclei Jets as the Origin of Ultrahigh-Energy Cosmic Rays and Perspectives for the Detection of Astrophysical Source Neutrinos at EeV Energies.

We demonstrate that a population of active galactic nuclei (AGN) can describe the observed spectrum of ultra-high-energy cosmic rays (UHECRs) at and above the ankle, and that the dominant contribution comes from low-luminosity BL Lacertae objects. An additional, subdominant contribution from high-luminosity AGN is needed to improve the description of the composition observables, leading to a substantial neutrino flux that peaks at exaelectronvolt (EeV) energies. We also find that different properties for the low- and high-luminosity AGN populations are required; a possibly similar baryonic loading can already be excluded from current IceCube Neutrino Observatory observations. We also show that the flux of neutrinos emitted from within the sources should outshine the cosmogenic neutrinos produced during the propagation of UHECRs. This result has profound implications for the ultra-high-energy (∼EeV) neutrino experiments, since additional search strategies can be used for source neutrinos compared to cosmogenic neutrinos, such as stacking searches, flare analyses, and multimessenger follow-ups.

Heavy decaying dark matter at future neutrino radio telescopes

In the next decades, ultra-high-energy neutrinos in the EeV energy range will be potentially detected by next-generation neutrino telescopes. Although their primary goals are to observe cosmogenic neutrinos and to gain insight into extreme astrophysical environments, they can also indirectly probe the nature of dark matter. In this paper, we study the projected sensitivity of up-coming neutrino radio telescopes, such as RNO-G, GRAND and IceCube-gen2 radio array, to decaying dark matter scenarios. We investigate different dark matter decaying channels and masses, from 107 to 1015 GeV. By assuming the observation of cosmogenic or newborn pulsar neutrinos, we forecast conservative constraints on the lifetime of heavy dark matter particles. We find that these limits are competitive with and highly complementary to previous multi-messenger analyses.

Study of a Large Array to Detect Ultra-high Energy Tau Neutrino

The $PeV$ cosmogenic neutrino is still interesting argument. Since cosmogenic neutrinos interact weakly with matter, the detection of their direction will precisely point out the source in the space. In this paper, we show the results of the simulation of tau lepton air showers induced by high energy neutrinos detected by an array of stations designed to use the Earth Skimming method improved by the "mountain chain screen" strategy. Both track time stamp and position information of the stations on the array are used to reconstruct the shower to estimate the direction and the number of events. The array studied consists of 640 stations ($40 \times 16$) spread over an area of $0.6\,km^2$ starting from $1500\,m$ above the sea level (a.s.l.) on $30^{o}$ inclined plane of the mountain. When we extrapolate to 3 years and 10 $km^2$ we estimate 13 tau lepton events in energy interval of 10 PeV to 1000 PeV detected using the present upper limits of tau neutrino flux.