167 research outputs found
Global phylogeography and ancient evolution of the widespread human gut virus crAssphage
Microbiomes are vast communities of microorganisms and viruses that populate all natural ecosystems. Viruses have been considered to be the most variable component of microbiomes, as supported by virome surveys and examples of high genomic mosaicism. However, recent evidence suggests that the human gut virome is remarkably stable compared with that of other environments. Here, we investigate the origin, evolution and epidemiology of crAssphage, a widespread human gut virus. Through a global collaboration, we obtained DNA sequences of crAssphage from more than one-third of the world's countries and showed that the phylogeography of crAssphage is locally clustered within countries, cities and individuals. We also found fully colinear crAssphage-like genomes in both Old-World and New-World primates, suggesting that the association of crAssphage with primates may be millions of years old. Finally, by exploiting a large cohort of more than 1,000 individuals, we tested whether crAssphage is associated with bacterial taxonomic groups of the gut microbiome, diverse human health parameters and a wide range of dietary factors. We identified strong correlations with different clades of bacteria that are related to Bacteroidetes and weak associations with several diet categories, but no significant association with health or disease. We conclude that crAssphage is a benign cosmopolitan virus that may have coevolved with the human lineage and is an integral part of the normal human gut virome
LeptonInjector and LeptonWeighter: A neutrino event generator and weighter for neutrino observatories
We present a high-energy neutrino event generator, called LeptonInjector,
alongside an event weighter, called LeptonWeighter. Both are designed for
large-volume Cherenkov neutrino telescopes such as IceCube. The neutrino event
generator allows for quick and flexible simulation of neutrino events within
and around the detector volume, and implements the leading Standard Model
neutrino interaction processes relevant for neutrino observatories:
neutrino-nucleon deep-inelastic scattering and neutrino-electron annihilation.
In this paper, we discuss the event generation algorithm, the weighting
algorithm, and the main functions of the publicly available code, with
examples.Comment: 28 pages, 10 figures, 3 table
In-situ estimation of ice crystal properties at the South Pole using LED calibration data from the IceCube Neutrino Observatory
The IceCube Neutrino Observatory instruments about 1 km3 of deep, glacial ice at the geographic South Pole using 5160 photomultipliers to detect Cherenkov light emitted by charged relativistic particles. A unexpected light propagation effect observed by the experiment is an anisotropic attenuation, which is aligned with the local flow direction of the ice. Birefringent light propagation has been examined as a possible explanation for this effect. The predictions of a first-principles birefringence model developed for this purpose, in particular curved light trajectories resulting from asymmetric diffusion, provide a qualitatively good match to the main features of the data. This in turn allows us to deduce ice crystal properties. Since the wavelength of the detected light is short compared to the crystal size, these crystal properties do not only include the crystal orientation fabric, but also the average crystal size and shape, as a function of depth. By adding small empirical corrections to this first-principles model, a quantitatively accurate description of the optical properties of the IceCube glacial ice is obtained. In this paper, we present the experimental signature of ice optical anisotropy observed in IceCube LED calibration data, the theory and parametrization of the birefringence effect, the fitting procedures of these parameterizations to experimental data as well as the inferred crystal properties.</p
Searching for eV-scale sterile neutrinos with eight years of atmospheric neutrinos at the IceCube neutrino telescope
We report in detail on searches for eV-scale sterile neutrinos, in the
context of a 3+1 model, using eight years of data from the IceCube neutrino
telescope. By analyzing the reconstructed energies and zenith angles of 305,735
atmospheric and events we construct confidence
intervals in two analysis spaces: vs.
under the conservative assumption ; and
vs. given sufficiently large that
fast oscillation features are unresolvable. Detailed discussions of the event
selection, systematic uncertainties, and fitting procedures are presented. No
strong evidence for sterile neutrinos is found, and the best-fit likelihood is
consistent with the no sterile neutrino hypothesis with a p-value of 8\% in the
first analysis space and 19\% in the second.Comment: This long-form paper is a companion to the letter "An eV-scale
sterile neutrino search using eight years of atmospheric muon neutrino data
from the IceCube Neutrino Observatory". v2: update other experiments contours
on results plo
An eV-scale sterile neutrino search using eight years of atmospheric muon neutrino data from the IceCube Neutrino Observatory
The results of a 3+1 sterile neutrino search using eight years of data from
the IceCube Neutrino Observatory are presented. A total of 305,735 muon
neutrino events are analyzed in reconstructed energy-zenith space to test for
signatures of a matter-enhanced oscillation that would occur given a sterile
neutrino state with a mass-squared differences between 0.01\,eV and
100\,eV. The best-fit point is found to be at
and , which is consistent with the no sterile
neutrino hypothesis with a p-value of 8.0\%.Comment: 11 pages, 5 figures. This letter is supported by the long-form paper
"Searching for eV-scale sterile neutrinos with eight years of atmospheric
neutrinos at the IceCube neutrino telescope," also appearing on arXiv.
Digital data release available at:
https://github.com/icecube/HE-Sterile-8year-data-releas
Searches for Neutrinos from Gamma-Ray Bursts using the IceCube Neutrino Observatory
Gamma-ray bursts (GRBs) are considered as promising sources of
ultra-high-energy cosmic rays (UHECRs) due to their large power output.
Observing a neutrino flux from GRBs would offer evidence that GRBs are hadronic
accelerators of UHECRs. Previous IceCube analyses, which primarily focused on
neutrinos arriving in temporal coincidence with the prompt gamma rays, found no
significant neutrino excess. The four analyses presented in this paper extend
the region of interest to 14 days before and after the prompt phase, including
generic extended time windows and targeted precursor searches. GRBs were
selected between May 2011 and October 2018 to align with the data set of
candidate muon-neutrino events observed by IceCube. No evidence of correlation
between neutrino events and GRBs was found in these analyses. Limits are set to
constrain the contribution of the cosmic GRB population to the diffuse
astrophysical neutrino flux observed by IceCube. Prompt neutrino emission from
GRBs is limited to 1% of the observed diffuse neutrino flux, and
emission on timescales up to s is constrained to 24% of the total
diffuse flux
Strong Constraints on Neutrino Nonstandard Interactions from TeV-Scale Μ Disappearance at IceCube
We report a search for nonstandard neutrino interactions (NSI) using eight years of TeV-scale atmospheric muon neutrino data from the IceCube Neutrino Observatory. By reconstructing incident energies and zenith angles for atmospheric neutrino events, this analysis presents unified confidence intervals for the NSI parameter ΔΌÏ. The best-fit value is consistent with no NSI at a p value of 25.2%. With a 90% confidence interval of â0.0041â€Î”ÎŒÏâ€0.0031 along the real axis and similar strength in the complex plane, this result is the strongest constraint on any NSI parameter from any oscillation channel to date
Search for Quantum Gravity Using Astrophysical Neutrino Flavour with IceCube
Along their long propagation from production to detection, neutrino states
undergo quantum interference which converts their types, or flavours.
High-energy astrophysical neutrinos, first observed by the IceCube Neutrino
Observatory, are known to propagate unperturbed over a billion light years in
vacuum. These neutrinos act as the largest quantum interferometer and are
sensitive to the smallest effects in vacuum due to new physics. Quantum gravity
(QG) aims to describe gravity in a quantum mechanical framework, unifying
matter, forces and space-time. QG effects are expected to appear at the
ultra-high-energy scale known as the Planck energy, ~giga-electronvolts (GeV). Such a high-energy universe would have
existed only right after the Big Bang and it is inaccessible by human
technologies. On the other hand, it is speculated that the effects of QG may
exist in our low-energy vacuum, but are suppressed by the Planck energy as
(~GeV), (~GeV), or its higher powers. The coupling of particles to these
effects is too small to measure in kinematic observables, but the phase shift
of neutrino waves could cause observable flavour conversions. Here, we report
the first result of neutrino interferometry~\cite{Aartsen:2017ibm} using
astrophysical neutrino flavours to search for new space-time structure. We did
not find any evidence of anomalous flavour conversion in IceCube astrophysical
neutrino flavour data. We place the most stringent limits of any known
technologies, down to ~GeV, on the dimension-six operators
that parameterize the space-time defects for preferred astrophysical production
scenarios. For the first time, we unambiguously reach the signal region of
quantum-gravity-motivated physics.Comment: The main text is 7 pages with 3 figures and 1 table. The Appendix
includes 5 pages with 3 figure
Searching for High-energy Neutrino Emission from Galaxy Clusters with IceCube
Galaxy clusters have the potential to accelerate cosmic rays (CRs) to ultrahigh energies via accretion shocks or embedded CR acceleration sites. The CRs with energies below the Hillas condition will be confined within the cluster and eventually interact with the intracluster medium gas to produce secondary neutrinos and gamma rays. Using 9.5 yr of muon neutrino track events from the IceCube Neutrino Observatory, we report the results of a stacking analysis of 1094 galaxy clusters with masses âł10 Mâ and redshifts between 0.01 and âŒ1 detected by the Planck mission via the SunyaevâZelâdovich effect. We find no evidence for significant neutrino emission and report upper limits on the cumulative unresolved neutrino flux from massive galaxy clusters after accounting for the completeness of the catalog up to a redshift of 2, assuming three different weighting scenarios for the stacking and three different power-law spectra. Weighting the sources according to mass and distance, we set upper limits at a 90% confidence level that constrain the flux of neutrinos from massive galaxy clusters (âł10 Mâ) to be no more than 4.6% of the diffuse IceCube observations at 100 TeV, assuming an unbroken Eâ power-law spectrum
A muon-track reconstruction exploiting stochastic losses for large-scale Cherenkov detectors
IceCube is a cubic-kilometer Cherenkov telescope operating at the South Pole.
The main goal of IceCube is the detection of astrophysical neutrinos and the
identification of their sources. High-energy muon neutrinos are observed via
the secondary muons produced in charge current interactions with nuclei in the
ice. Currently, the best performing muon track directional reconstruction is
based on a maximum likelihood method using the arrival time distribution of
Cherenkov photons registered by the experiment's photomultipliers. A known
systematic shortcoming of the prevailing method is to assume a continuous
energy loss along the muon track. However at energies TeV the light yield
from muons is dominated by stochastic showers. This paper discusses a
generalized ansatz where the expected arrival time distribution is parametrized
by a stochastic muon energy loss pattern. This more realistic parametrization
of the loss profile leads to an improvement of the muon angular resolution of
up to for through-going tracks and up to a factor 2 for starting tracks
over existing algorithms. Additionally, the procedure to estimate the
directional reconstruction uncertainty has been improved to be more robust
against numerical errors
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