PeV Neutrino Events Research Articles

Could TDE outflows produce the PeV neutrino events?

ABSTRACT A tidal disruption event (TDE), AT2019dsg, was observed to be associated with a PeV neutrino event, IceCube-191001A, lagging the optical outburst by a half year. It is known that TDEs may generate ultra fast outflows. If the TDE occurs in a cloudy environment, the outflow-cloud interactions may form shock waves which generate accelerated protons and hence, delayed neutrinos from hadronic interactions in clouds. Here, we investigate the neutrino production in AT2019dsg by examining the TDE outflow-cloud interaction model. We find that, for an outflow with a velocity of 0.07 c and a kinetic luminosity of $10^{45}\rm \,erg\ \,s^{-1}$, protons may be accelerated up to ∼60 PeV by the bow shocks, and generate PeV neutrinos by interactions with clouds. The predicted neutrino number in this model depends on the uncertainties of model parameters and in order to match the observations, some challenging values of parameters have been involved. The PeV neutrino event number can be ∼4 × 10−3 for a hard proton index Γ = 1.5.

Ultra-high energy cosmic neutrinos from gamma-ray bursts

Based on the recent association of IceCube TeV and PeV neutrino events with gamma-ray bursts (GRBs) by considering the Lorentz violation of neutrinos, we provide a new estimate on the GRB neutrino flux with a more significant result compared to the previous constraint by the IceCube Collaboration. Among these 24 neutrino “shower” events above 60 TeV, 12 events are associated with GRBs. Such a result is compatible with the prediction from GRB fireball models. Analysis of track events provides a consistent result with the shower events to associate high energy cosmic neutrinos with GRBs under the same Lorentz violation features of neutrinos. We also make a background estimation and reveal GRBs as a significant source for the ultra-high energy IceCube neutrino events. Our work supports the Lorentz violation and CPT-violation of neutrinos, indicating new physics beyond relativity.

Cosmic rays, neutrinos, and GeV-TeV gamma rays from starburst galaxy NGC 4945

The detection of high-energy astrophysical neutrinos and ultra-high-energy cosmic rays (UHECRs) provides a new way to explore sources of cosmic rays. One of the highest energy neutrino events detected by IceCube, tagged as IC35, is close to the UHECR anisotropy region detected by Pierre Auger Observatory. The nearby starburst (SB) galaxy, NGC 4945, is close to this anisotropic region and inside the mean angular error of the IC35 event. Considering the hypernovae contribution located in the SB region of NGC 4945, which can accelerate protons up to $\ensuremath{\sim}{10}^{17}\text{ }\text{ }\mathrm{eV}$ and inject them into the interstellar medium, we investigate the origin of this event around this starburst galaxy. We show that the interaction of these protons with the SB region's gas density could explain Fermi-LAT gamma-ray and radio observations if the magnetic field's strength in the SB region is the order of $\ensuremath{\sim}\mathrm{mG}$. Our estimated PeV neutrino events, in ten years, for this source is approximately 0.01 ($4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$) if a proton spectral index of 2.4 (2.7) is considered, which would demonstrate that IC35 is not produced in the central region of this SB galaxy. Additionally, we consider the superwind region of NGC 4945 and show that protons can hardly be accelerated in it up to UHECRs.

Estimation of baryon asymmetry from dark matter decaying into IceCube neutrinos

The recent results of IceCube Neutrino Observatory include an excess of PeV neutrino events which appear to follow a broken power-law different from the other lower energy neutrinos detected by IceCube. The possible astrophysical source of these neutrinos is still unknown. One possible source of such neutrinos could be the decay of nonthermal, long-lived heavy mass dark matter, whose mass should be [Formula: see text] GeV and could have produced at the very early Universe. They can undergo cascading decay via both hadronic and leptonic channels to finally produce such high energy neutrinos. This possibility has been explored in this work by studying the decay flux of these dark matter candidates. The mass and lifetime of such dark matter particles have been obtained by performing a [Formula: see text] fit with the PeV neutrino data of IceCube. We finally estimate the baryon asymmetry produced in the Universe due to such dark matter decay.

Multi-component fermionic dark matter and IceCube PeV scale neutrinos in left-right model with gauge unification

We consider a simple extension of the minimal left-right symmetric model (LRSM) in order to explain the PeV neutrino events seen at the IceCube experiment from a heavy decaying dark matter. The dark matter sector is composed of two fermions: one at PeV scale and the other at TeV scale such that the heavier one can decay into the lighter one and two neutrinos. The gauge annihilation cross sections of PeV dark matter are not large enough to generate its relic abundance within the observed limit. We include a pair of real scalar triplets ΩL,R which can bring the thermally overproduced PeV dark matter abundance into the observed range through late time decay and consequent entropy release thereby providing a consistent way to obtain the correct relic abundance without violating the unitarity bound on dark matter mass. Another scalar field, a bitriplet under left-right gauge group is added to assist the heavier dark matter decay. The presence of an approximate global U(1)X symmetry can naturally explain the origin of tiny couplings required for long-lived nature of these decaying particles. We also show, how such an extended LRSM can be incorporated within a non-supersymmetric SO(10) model where the gauge coupling unification at a very high scale naturally accommodate a PeV scale intermediate symmetry, required to explain the PeV events at IceCube.

Searching for PeV neutrinos from photomeson interactions in magnetars

In this paper we estimate the flux of PeV neutrinos and gamma-rays from magnetar polar caps, assuming that ions/protons are injected, and accelerated in these regions and interact with the radiative background. The present study takes into account the effect of the photon splitting mechanisms that should modify the radiative background, and enhance the neutrino and gamma-ray fluxes at PeV energies, with a view to explain the PeV neutrino events detected in IceCube. The results indicate that in the near future, the possibility of any significant excess of neutrino events from a magnetar in the Milky Way is extremely low. Further, we suggest that the simultaneous observation of neutrinos and gamma-rays at Earth from expanded “Gen2” IceCube detector and/or High Altitude Water Cherenkov Observatory would provide opportunities to explore the possible origin of very high-energy neutrinos and gamma-rays.

IceCube Events from Decaying Dark Matter with Neutrino Portal

IceCube has observed several PeV neutrino events whose astrophysical origin has not been identified. In this proceeding, we discuss heavy decaying dark matter may be responsible for these neutrinos. Dark matter [Formula: see text] is constructed to communicate with standard model particles through the neutrino-portal interaction. We calculate both total and differential decay width for the dominant three-body decay of dark matter and show that to fit the data, the required mass is around [Formula: see text](10 PeV) and lifetime is about [Formula: see text]s.

TANAMI: Multiwavelength and multimessenger observations of active galaxies

AbstractExtragalactic jets launched from the immediate vicinity of supermassive black holes in radio‐loud active galactic nuclei (AGN) are key objects in modern astronomy and astroparticle physics. AGN jets carry a fraction of the total gravitational energy released during the accretion of matter onto supermassive black holes and are prime suspects as possible sources of ultrahigh‐energy cosmic rays and the recently detected extraterrestrial neutrinos at PeV energies. TANAMI (Tracking Active galactic Nuclei with Austral Milliarcsecond Interferometry) is a multiwavelength program monitoring AGN jets of the southern sky. It combines high‐resolution imaging and spectral monitoring at radio wavelengths with higher‐frequency observations at IR, optical/UV, X‐ray, and γ‐ray energies. We review recent results of the TANAMI program, highlighting AGN candidate neutrino‐emitters in the error circles of the IceCube PeV neutrino events. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Some possible sources of IceCube TeV–PeV neutrino events

The IceCube Collaboration has observed 37 neutrino events in the energy range $30\, TeV\leq E_{\nu} \leq 2$ PeV and the sources of these neutrinos are unknown. Here we have shown that positions of 12 high energy blazars and the position of the FR-I galaxy Centaurus A, coincide within the error circles of ten IceCube events, the later being in the error circle of the highest energy event so far observed by IceCube. Two of the above blazars are simultaneously within the error circles of the Telescope Array hotspot and one IceCube event. We found that the blazar H2356-309 is within the error circles of three IceCube events. We propose that photohadronic interaction of the Fermi accelerated high energy protons with the synchrotron/SSC background photons in the nuclear region of these high energy blazars and AGN are probably responsible for some of the observed IceCube events.

ANTARES constrains a blazar origin of two IceCube PeV neutrino events

The source(s) of the neutrino excess reported by the IceCube Collaboration is unknown. The TANAMI Collaboration recently reported on the multiwavelength emission of six bright, variable blazars which are positionally coincident with two of the most energetic IceCube events. Objects like these are prime candidates to be the source of the highest-energy cosmic rays, and thus of associated neutrino emission. We present an analysis of neutrino emission from the six blazars using observations with the ANTARES neutrino telescope.The standard methods of the ANTARES candidate list search are applied to six years of data to search for an excess of muons --- and hence their neutrino progenitors --- from the directions of the six blazars described by the TANAMI Collaboration, and which are possibly associated with two IceCube events. Monte Carlo simulations of the detector response to both signal and background particle fluxes are used to estimate the sensitivity of this analysis for different possible source neutrino spectra. A maximum-likelihood approach, using the reconstructed energies and arrival directions of through-going muons, is used to identify events with properties consistent with a blazar origin.Both blazars predicted to be the most neutrino-bright in the TANAMI sample (1653$-$329 and 1714$-$336) have a signal flux fitted by the likelihood analysis corresponding to approximately one event. This observation is consistent with the blazar-origin hypothesis of the IceCube event IC14 for a broad range of blazar spectra, although an atmospheric origin cannot be excluded. No ANTARES events are observed from any of the other four blazars, including the three associated with IceCube event IC20. This excludes at a 90\% confidence level the possibility that this event was produced by these blazars unless the neutrino spectrum is flatter than $-2.4$.

The Glashow resonance in neutrino–photon scattering

Reactions νlγ→W+l−(l=e,μ,τ) near the threshold s=mW+ml are analyzed. Two independent calculations of the corresponding cross sections (straightforward calculations using the Standard Electroweak Lagrangian and calculations in the framework of the parton model) are compared. It is shown that the Standard Electroweak Theory strongly suggests that these reactions proceed via the Glashow resonances. Accordingly, a hypothesis that the on-shell W bosons in the reactions νlγ→W+l− are the Glashow resonances is put forward. A role of these reactions for testing T symmetry is discussed. A model with T-violating Glashow resonances for description of the distribution of the TeV–PeV neutrino events recently observed by the IceCube Collaboration is presented.

Photopion production in black-hole jets and flat-spectrum radio quasars as PeV neutrino sources

The IceCube Collaboration has reported neutrinos with energies between ∼30 TeV and a few PeV that are significantly enhanced over the cosmic-ray induced atmospheric background. Viable high-energy neutrino sources must contain very high-energy and ultra-high-energy cosmic rays while efficiently making PeV neutrinos. Gamma-ray Bursts (GRBs) and blazars have been considered as candidate cosmic-ray accelerators. GRBs, including low-luminosity GRBs, can be efficient PeV neutrino emitters for low bulk Lorentz factor outflows, although the photopion production efficiency needs to be tuned to simultaneously explain ultra-high-energy cosmic rays. Photopion production efficiency of cosmic rays accelerated in the inner jets of flat spectrum radio quasars (FSRQs) is ∼1–10% due to interactions with photons of the broad-line region (BLR), whereas BL Lac objects are not effective PeV neutrino sources due to the lack of external radiation fields. Photopion threshold effects with BLR photons suppress neutrino production below ∼1 PeV, which implies that neutrinos from other sources would dominate over the diffuse neutrino intensity at sub-PeV energies. Reduction of the ≫ PeV neutrino flux can be expected when curving cosmic-ray proton distributions are employed. Considering a log-parabolic function to describe the cosmic-ray distribution, we discuss possible implications for particle acceleration in black-hole jets. Our results encourage a search for IceCube PeV neutrino events associated with γ-ray loud FSRQs using Fermi-LAT data. In our model, as found in our previous work, the neutrino flux is suppressed below 1 PeV, which can be tested with increased IceCube exposure.

Cosmic-ray neutrinos from the decay of long-lived particle and the recent IceCube result

Motivated by the recent IceCube result, we study high energy cosmic-ray neutrino flux from the decay of a long-lived particle. Because neutrinos are so transparent, high energy neutrinos produced in the past may also contribute to the present neutrino flux. We point out that the PeV neutrino events observed by IceCube may originate in the decay of a particle much heavier than PeV if its lifetime is shorter than the present cosmic time. It is shown that the mass of the particle responsible for the IceCube event can be as large as ∼1010 GeV. We also discuss several possibilities to acquire information about the lifetime of the long-lived particle.

How many of the observed neutrino events can be described by cosmic ray interactions in the Milky Way?

Cosmic rays diffuse through the interstellar medium and interact with matter and radiations as long as they are trapped in the Galactic magnetic field. The IceCube experiment has detected some TeV–PeV neutrino events whose origin is yet unknown. We study if all or a fraction of these events can be described by the interactions of cosmic rays with matter. We consider the average target density needed to explain them for different halo sizes and shapes, the effect of the chemical composition of the cosmic rays, the impact of the directional information of the neutrino events, and the constraints from gamma-ray bounds and their direction. We do not require knowledge of the cosmic ray escape time or injection for our approach. We find that, given all constraints, at most 0.1 of the observed neutrino events in IceCube can be described by cosmic ray interactions with matter. In addition, we demonstrate that the currently established chemical composition of the cosmic rays contradicts a peak of the neutrino spectrum at PeV energies.

Superheavy particle origin of IceCube PeV neutrino events

We interpret the PeV shower events observed by the IceCube Collaboration as an s-channel enhancement of neutrino–quark scattering by a leptoquark that couples to the τ-flavor and light quarks. With a leptoquark mass around 0.6 TeV and a steep 1/E2.3 neutrino flux, charged-current scattering gives cascade events at ∼1 PeV and neutral-current scattering gives cascade events at ∼0.5 PeV. This mechanism is also consistent with the paucity of muon-track events above 100 TeV.

Galactic PeV neutrinos

The IceCube experiment has detected two neutrinos with energies between 1 and 10PeV. They might have originated from Galactic or extragalactic sources of cosmic rays. In the present work we consider hadronic interactions of the diffuse very high energy cosmic rays with the interstellar matter within our Galaxy to explain the PeV neutrino events detected in IceCube. We also expect PeV gamma ray events along with the PeV neutrino events if the observed PeV neutrinos were produced within our Galaxy in hadronic interactions. PeV gamma rays are unlikely to reach us from sources outside our Galaxy due to pair production with cosmic background radiation fields. We suggest that in future with simultaneous detections of PeV gamma rays and neutrinos it would be possible to distinguish between Galactic and extragalactic origins of very high energy neutrinos.

Neutrinos at IceCube from heavy decaying dark matter

A monochromatic line in the cosmic neutrino spectrum would be a smoking gun signature of dark matter. It is intriguing that the IceCube experiment has recently reported two PeV neutrino events with energies that may be equal up to experimental uncertainties, and which have a probability of being a background fluctuation estimated to be less than a percent. Here we explore prospects for these events to be the first indication of a monochromatic line signal from dark matter. While measurable annihilation signatures would seem to be impossible at such energies, we discuss the dark matter quantum numbers, effective operators, and lifetimes which could lead to an appropriate signal from dark matter decays. We will show that the set of possible decay operators is rather constrained, and will focus on several viable candidates which could explain the IceCube events; R-parity violating gravitinos, hidden sector gauge bosons, and singlet fermions in an extra dimension. In essentially all cases we find that a PeV neutrino line signal from dark matter would be accompanied by a potentially observable continuum spectrum of neutrinos rising towards lower energies.

IceCube: From Oscillations to PeV Neutrino Events

With IceCube and its low-energy extension DeepCore, an instrument with a combined energy range from tens of GeV to EeV has been commissioned. It measures the atmospheric neutrino spectrum from the lower energies where neutrinos oscillate to energies as large as 100 TeV with a statistic of more than 100,000 events per year. The initial results suggest that IceCube can measure the oscillation parameters in an energy range that exceeds existing observations by one order of magnitude, thus opening a new window on neutrino physics. We also discuss the observation of PeV-energy events that cannot be accommodated by the flux anticipated by extrapolation of present atmospheric neutrino measurements.