Cosmogenic Neutrinos Research Articles

Neutrinos as a Probe of Ultra-High Energy Cosmic Rays

The search for astrophysical high-energy neutrinos is one of the pillars of multi-messenger astronomy. Neutrino production in extragalactic sources or the cosmic environment is intimately related to (and limited by) the observed emission of γ-rays and cosmic rays. We will review the various indirect neutrino limits that arise from this cosmic connection. So far, no high-energy neutrino source could be unambiguously identified. However, the strong limits on TeV to PeV neutrino emission set by this non-observation serve as an indirect constraint of candidate sources of cosmic rays. At the EeV energy scale the diffuse flux of cosmogenic neutrinos associated with the propagation of ultra-high energy cosmic rays in the cosmic radiation background seems to be the most promising candidate for a future detection. We will discuss its model dependence w.r.t. nuclear composition and evolution of the sources and provide simple bolometric scaling relations and lower limits.

CHERENKOV RADIATION INDUCED BY COSMOGENIC NEUTRINOS IN NEAR-FIELD

The radio technique of cosmogenic neutrino detection, which relies on the Cherenkov signals coherently emitted from the particle showers in dense medium, has now become a mature field. We present an alternative approach to calculate such Cherenkov pulse by a numerical code based on the finite difference time-domain (FDTD) method that does not rely on the far-field approximation. We show that for a shower elongated by the LPM (Landau-Pomeranchuk-Migdal) effect and thus with a multi-peak structure, the generated Cherenkov signal will always be a bipolar and asymmetric waveform in the near-field regime regardless of the specific variations of the multi-peak structure, which makes it a generic and distinctive feature. This should provide an important characteristic signature for the identification of ultra-high energy cosmogenic neutrinos.

Very high energy photons and neutrinos: Implications for UHECR

Depending on the environment of the acceleration processes for ultra-high energy cosmic rays, photons and neutrinos may be produced by interactions in the sources. If so, observations of gamma-rays or neutrinos could pinpoint the sources. This paper reviews some aspects of the search for photons and neutrinos from possible sources of ultra-high energy cosmic rays. Both photons and neutrinos are potential tracers of sites of cosmic-ray acceleration because, being neutral, they are not deviated by intervening magnetic fields. Photons are plentiful, but their interpretation is complicated by interactions in the sources and spectral modifications due to cascading in transit. In addition, their origin can be from radiation by electrons as well as from decay of neutral pions. In contrast, high-energy neutrinos would directly imply acceleration of hadrons. Because they interact only weakly, neutrinos are not distorted by interactions in the sources, but for the same reason they are hard to detect. Photons and neutrinos provide complementary types of information about cosmic-ray sources, but they both indicate underlying acceleration of charged particles. It is therefore natural to select known sources of TeV gamma-rays as potential sources of neutrinos. It is useful to distinguish two ways of producing gamma-rays and neutrinos: at the sources of ultra-high energy cosmic rays (UHECR) and during propagation through the cosmos. In the first case, the observed spectra of the neutral messengers ( and ν) depend on the source spectrum, on cosmic evolution of the sources and on conditions inside or near the acceleration region. Cosmogenic neutrinos and photons produced during propagation of UHECR depend on the injected spectrum as a function of energy and red shift, but not on conditions at the sources. It is generally assumed that the highest energy cosmic rays are accelerated in extra-galactic sources, and that the transition from the lower energy population of galactic cosmic rays occurs somewhere between 0.3 and 3EeV. Protons and nuclei with energies above 30EeV begin to suffer significant energy losses during propagation from sources more distant than a few hundred Mpc. Ten EeV, being below the suppression energy, but above the transition region is a suitable energy around which to estimate the energy content of the cosmic rays from extra-galactic sources. The observed energy flux at 10EeV by HiRes (1) and Telescope Array (2 )i s

Detection of cosmogenic neutrinos with the KM3NeT telescope

Cosmogenic neutrinos are produced during the propagation of ultra high energy cosmic rays (UHECR) through the cosmological microwave background radiation. The extragalactic origin of UHECR guarantees generation of high energy cosmogenic neutrinos, however, the flux depends on the currently unknown properties of UHECR, for example, the chemical composition and distribution of the sources and their evolution with redshift. Estimations of cosmogenic neutrino fluxes, which are constrained by UHECR observations, include a range of models in which a detectable signal could be produced in a very large volume high-energy neutrino telescope. In particular the favorable scenarios are based on the models with a pure proton composition. The possible event rate of cosmogenic neutrinos in the KM3NeT telescope for the different flux models is discussed in this paper.

Status of RadioWave Neutrino Detection

As of this writing, there are three dedicated experiments, all based in Antarctica, which seek first-ever measurement of the ultra-high energy neutrino flux at Earth. All three (ANITA, ARA and ARIANNA) exploit the Askaryan Effect to detect the so-called cosmogenic neutrinos which should result from interactions of ultra-high energy baryons with the Cosmic Microwave Background Radiation (CMBR). Photoproduction of those neutrinos, via Nγ → Δ → Nπ±, with subsequent weak decays of those pions resulting in neutrinos. In-ice weak and neutral scattering of those neutrinos off ice molecules can yield in a detectable pulse of coherent, radio-frequency radiation. We summarize the three experiments, and discuss prospects.

A REVIEW OF PARTICLE ASTROPHYSICS WITH ICECUBE

IceCube is a neutrino detector sensitive to energies above 10 GeV. IceCube operates by sensing the Cherenkov light from secondary particles produced in neutrino-matter interactions. One gigaton of highly transparent Antarctic ice is instrumented to achieve this goal. Designed to be modular, IceCube has been collecting data since construction began in 2005. Construction was completed in December 2010. The primary goal of IceCube is to observe astrophysical sources of neutrinos. We present here a summary of IceCube's recent results in atmospheric neutrinos, point sources, diffuse fluxes of neutrinos, cosmogenic neutrinos, a lack of correlation between neutrinos and Gamma Ray Bursts and the search for dark matter.

The neutrino sky at very high energies

Neutrino astronomy opens a new window for the observation and study of high-energy phenomena in our Universe. The emission of high-energy neutrinos in extragalactic sources or the cosmic environment is intimately related to that of γ-rays and cosmic rays. We will review the various indirect neutrino limits that arise from this cosmic connection and compare this to the present direct limits of neutrino observatories. Specific models of extragalactic TeV to PeV neutrino sources are already testable by large volume neutrino observatories like IceCube. At the EeV energy scale the flux of cosmogenic neutrinos associated with the propagation of ultra-high energy cosmic rays in the cosmic radiation background seems to be the most promising contribution to the diffuse neutrino background. We will discuss its model dependence w.r.t. chemical composition and evolution of the sources and provide simple bolometric scaling relations.

Implications of ultrahigh energy neutrino flux constraints for Lorentz-invariance violating cosmogenic neutrinos

We consider the implications of Lorentz-invariance violation (LIV) on cosmogenic neutrino observations, with particular focus on the constraints imposed on several well-developed models for ultrahigh energy cosmogenic neutrino production by recent results from the ANITA long-duration balloon payload, and RICE at the South Pole. Under a scenario proposed originally by Coleman and Glashow, each lepton family may attain maximum velocities that can exceed $c$, leading to energy-loss through several interaction channels during propagation. We show that future observations of cosmogenic neutrinos will provide by far the most stringent limit on LIV in the neutrino sector. We derive the implied level of LIV required to suppress observation of predicted fluxes from several mainstream cosmogenic neutrino models, and specifically those recently constrained by the ANITA and RICE experiments. We simulate via detailed Monte Carlo code the propagation of cosmogenic neutrino fluxes in the presence of LIV-induced energy losses. We show that this process produces several detectable effects in the resulting attenuated neutrino spectra, even at LIV-induced neutrino superluminality of $({u}_{\ensuremath{\nu}}\ensuremath{-}c)/c\ensuremath{\simeq}{10}^{\ensuremath{-}26}$, about 13 orders of magnitude below current bounds.

Minimal cosmogenic neutrinos

The observed flux of ultra-high energy (UHE) cosmic rays (CRs) guarantees the presence of high-energy cosmogenic neutrinos that are produced via photo-hadronic interactions of CRs propagating through intergalactic space. This flux of neutrinos doesn't share the many uncertainties associated with the environment of the yet unknown CR sources. Cosmogenic neutrinos have nevertheless a strong model dependence associated with the chemical composition, source distribution or evolution and maximal injection energy of UHE CRs. We discuss a lower limit on the cosmogenic neutrino spectrum which depends on the observed UHE CR spectrum and composition and relates directly to experimentally observable and model-independent quantities. We show explicit limits for conservative assumptions about the source evolution.

The JEM-EUSO Mission to Explore the Extreme Universe

The JEM-EUSO mission will explore the origin of the extreme energy comic-rays (EECRs) above 1020eV and and can shed new light on some topics of fundamental physics. It is planned to be launched by a H2B rocket on 2017 and transferred to ISS by the H2 Transfer Vehicle (HTV), where it will be attached to the external experiment platform of KIBO. The super-wide-field of view (60 degrees) telescope, with a diameter of about 2.5m looks down the night-side atmosphere of the Earth from ∼400 km of altitude, to detect near UV photons (330–400nm, both fluorescent and Cherenkov) emitted by giant air-showers produced by EECRs. The instrument is design to observe between 500 and 800 events above 55 EeV in its first 3 yr of operation, as well as an exposure larger than 1 million km2 str yr at 3×1020eV 5 yr after launch. At these energies cosmic rays carry directional information and the arrival direction map will allow the identification of point sources of EECR, in case they exist, and of their astronomical counterparts. The comparison among the energy spectra of the spatially resolved individual sources will clarify the acceleration/emission mechanism, and also probe the Greisen-Zatsepin-Kuzmin process for the validation of Lorentz invariance up to γ∼1011. Neutral components (neutrinos and gamma rays) can also be detected if their fluxes are high enough. In fact, few cosmogenic neutrinos per year can be expected under conservative assumptions.

The Askaryan Radio Array

AbstractUltra high energy cosmogenic neutrinos could be most efficiently detected in dense, radio frequency (RF) transparent media via the Askaryan effect. Building on the expertise gained by RICE, ANITA and IceCube's radio extension in the use of the Askaryan effect in cold Antarctic ice, we are currently developing an antenna array known as ARA (The Askaryan Radio Array) to be installed in boreholes extending 200 m below the surface of the ice near the geographic South Pole. The unprecedented scale of ARA, which will cover a fiducial area of ≈ 100 square kilometers, was chosen to ensure the detection of the flux of neutrinos suggested by the observation of a drop in high energy cosmic ray flux consistent with the GZK cutoff by HiRes and the Pierre Auger Observatory. Funding to develop the instrumentation and install the first prototypes has been granted, and the first components of ARA were installed during the austral summer of 2010–2011. Within 3 years of commencing operation, the full ARA will exceed the sensitivity of any other instrument in the 0.1-10 EeV energy range by an order of magnitude. The primary goal of the ARA array is to establish the absolute cosmogenic neutrino flux through a modest number of events. This information would frame the performance requirements needed to expand the array in the future to measure a larger number of neutrinos with greater angular precision in order to study their spectrum and origins.

High Energy Neutrino Astronomy

The short review of theoretical aspects of ultra high energy (UHE) neutrinos. The accelerator sources, such as Supernovae remnants, Gamma Ray Bursts, AGN etc are discussed. The top-down sources include Topological Defects (TDs), Superheavy Dark Matter (SHDM) and Mirror Matter. The diffuse fluxes are considered accordingly as that of cosmogenic and top-down neutrinos. Much attention is given to the cascade upper limit to the diffuse neutrino fluxes in the light of Fermi-LAT data on diffuse high energy gamma radiation. This is most general and rigorous upper limit, valid for both cosmogenic and top-down models. At present upper limits from many detectors are close to the cascade upper limit, and 5 yr IceCube upper limit will be well below it.

Results from the ANITA-II Search for Ultra-High Energy Neutrinos

The ANtarctic Impulsive Transient Antenna (ANITA) is a balloon-borne radio telescope, designed to detect coherent Cherenkov emission from cosmogenic ultra-high energy (UHE) neutrinos (E>1018 eV). In a blind analysis of data from the second flight of ANITA, we find one candidate neutrino event on a background (thermal and man-made noise) of 0.97 ± 0.42, and set the strongest limit to date on the cosmogenic neutrino flux from 1018–1021 eV.

Neutron oscillations to parallel world: earlier end to the cosmic ray spectrum?

Present experimental data do not exclude fast oscillation of the neutron n to its degenerate twin from a hypothetical parallel sector, the so called mirror neutron n′. We show that this effect brings about remarkable modifications of the ultrahigh-energy cosmic ray spectrum testable by the present Pierre Auger Observatory (PAO) and Telescope Array (TA) detector, and the future JEM-EUSO experiment. In particular, the baryon non-conservation during UHECR propagation at large cosmological distances shifts the beginning of the GZK cutoff to lower energies, while in the presence of mirror sources it may enhance the spectrum at E>100 EeV. As a consequence, one can expect a significant reduction of the diffuse cosmogenic neutrino flux.

Restrictions on cosmogenic neutrinos and UHECR from Fermi 3 years data

Ultra-high energy cosmic ray protons accelerated in astrophysical objects produce secondary electromagnetic cascades during propagation in the cosmic microwave and infrared backgrounds. Those cascades contribute to the GeV-TeV diffuse photon flux, measured by Fermi LAT experiment. Recent studies of 3 years of Fermi LAT data have shown that diffuse gamma-ray background at E > 10GeV is about factor of 2 smaller then original one year data. This affects both models of UHECR and secondary cosmogenic neutrino fluxes. We show the allowed range of cosmogenic neutrino fluxes scanning over unknown UHECR parameters such as injected proton maximum energy and power law index, evolution of sources, systematic shift of UHECR energy scale. We consider three evolution models in which the UHECR sources are assumed to have the same evolution of either the star formation rate (SFR), or the gamma-ray burst (GRB) rate, or the active galactic nuclei (AGN) rate in the Universe and found that the last two are disfavored (and in the dip model rejected) by the new VHE gamma-ray background. We show that the largest fluxes predicted in the dip model would be detectable by IceCube in about 10 years of observation and are within the reach of a few years of observation with the ARA project. In the incomplete UHECR model in which protons are assumed to dominate only above 1019 eV, the cosmogenic neutrino fluxes could be a factor of 2 or 3 larger.

The Askar'yan Radio Array

We are developing an antenna array to be installed in boreholes extending 200 m below the ice surface at the geographic South Pole. ARA will cover a fiducial area of 150 km2, chosen to ensure the detection of the flux of neutrinos guaranteed by observations of the GZK cutoff by HiRes and the Pierre Auger Observatory. The first components of ARA were installed during the austral summer of 2010-2011. After three years of operation, the full array sensitivity will exceed that of any other instrument in the 0.1-10 EeV energy range by an order of magnitude. The primary goal of the ARA experiment is to establish the absolute cosmogenic neutrino flux through a modest number of events. This talk will describe the array, its science goals, and give the current status of the project.

High-energy neutrino astronomy

Neutrino astronomy, conceptually conceived four decades ago, has entered an exciting phase for providing results on the quest for the sources of the observed highest energy particles. IceCube and ANTARES are now completed and are scanning in space and time possible signals of high energy neutrinos indicating the existence of such sources. DeepCore, inside IceCube, is a playground for vetoed neutrino measurement with better potential below 1 TeV. A larger and denser detector is now being discussed. ARA, now in test phase, will be composed by radio stations that could cover up to ∼ 100 km2 and aims at the highest energy region of cosmogenic neutrinos. The non observation of cosmic events is on one side a source of disappointment, on the other it represents by itself an important result. If seen in the context of a multi-messenger science, the combination of photon and cosmic ray experiment results brings invaluable information. The experimental upper bounds of the cubic-kilometer telescope IceCube are now below the theoretical upper bounds for extragalactic fluxes of neutrinos from optically thin sources. These are responsible for accelerating the extragalactic cosmic rays. Such limits constrain the role of gamma-ray bursts, described by the fireball picture, as sources of ultra-high energy cosmic rays. Neutrino telescopes are exciting running multi-task experiments that produce astrophysics and particle physics results some of which have been illustrated at this conference and are summarized in this report.

Ultrahigh energy neutrinos from population III stars: Concept and constraints

We reconsider the model of neutrino production during the 'bright phase', first suggested in 1977, in the light of modern understanding of the role of Pop III stars and acceleration of particles in supernova shocks. We concentrate on the production of cosmogenic UHE neutrinos in supernova explosions that accompany the death of Pop III stars. Accelerated protons produce neutrinos in collisions with CMB photons. We deliberately use simplified assumptions which make our results transparent. Pop III stars are assumed to be responsible for the reionization of the universe as observed by WMAP. Since the evolution of Pop III stars is much faster than the Hubble rate, we consider the burst of UHE proton production to occur at fixed redshift (z_b=10-20). We discuss the formation of collisionless shocks and particle acceleration in the early universe. The composition of accelerated particles is expected to be proton dominated. A simple calculation is presented to illustrate the fact that the diffuse neutrinos flux from the bright phase burst is concentrated in a relatively narrow range around $7.5 \times 10^{15}(20/z_b)^2$ eV. The $\nu_\mu$ flux may be detectable by IceCube without violating the cascade upper limit and the expected energetics of SNe associated with Pop III stars. A possible signature of the neutrino production from Pop III stars may be the detection of resonant neutrino events. For the burst at $z_b=20$ and $\bar{\nu}_e$-flux at the cascade upper limit, the number of resonant events in IceCube may be as high as 10 events in 5 years of observations. These events have equal energies, $E=6.3\times 10^{15}$ eV, in the form of e-m cascades. Given the large uncertainties in the existing predictions of UHE cosmogenic neutrino fluxes, we argue that neutrinos from the first stars might become one of the most reliable hopes for UHE neutrino astronomy.

Constraints on the origin of the ultrahigh energy cosmic rays using cosmic diffuse neutrino flux limits: An analytical approach

Astrophysical neutrinos are expected to be produced in the interactions of ultra-high energy cosmic-rays with surrounding photons. The fluxes of the astrophysical neutrinos are highly dependent on the characteristics of the cosmic-ray sources, such as their cosmological distributions. We study possible constraints on the properties of cosmic-ray sources in a model-independent way using experimentally obtained diffuse neutrino flux above 100 PeV. The semi-analytic formula is derived to estimate the cosmogenic neutrino fluxes as functions of source evolution parameter and source extension in redshift. The obtained formula converts the upper-limits on the neutrino fluxes into the constraints on the cosmic-ray sources. It is found that the recently obtained upper-limit on the cosmogenic neutrinos by IceCube constrains the scenarios with strongly evolving ultra-high energy cosmic-ray sources, and the future limits from an 1 km^3 scale detector are able to further constrain the ultra-high energy cosmic-rays sources with evolutions comparable to the cosmic star formation rate.

Disappointing model for ultrahigh-energy cosmic rays

Data of Pierre Auger Observatory show a proton-dominated chemical composition of ultrahigh-energy cosmic rays spectrum at (1 – 3) EeV and a steadily heavier composition with energy increasing. In order to explain this feature we assume that (1 – 3) EeV protons are extragalactic and derive their maximum acceleration energy, Epmax ≃ 4 EeV, compatible with both the spectrum and the composition. We also assume the rigidity-dependent acceleration mechanism of heavier nuclei, EAmax = Z × Epmax. The proposed model has rather disappointing consequences: i) no pion photo-production on CMB photons in extragalactic space and hence ii) no high-energy cosmogenic neutrino fluxes; iii) no GZK-cutoff in the spectrum; iv) no correlation with nearby sources due to nuclei deflection in the galactic magnetic fields up to highest energies.