662 research outputs found
Extracting the Energy-Dependent Neutrino-Nucleon Cross Section Above 10 TeV Using IceCube Showers
Neutrinos are key to probing the deep structure of matter and the high-energy
Universe. Yet, until recently, their interactions had only been measured at
laboratory energies up to about 350 GeV. An opportunity to measure their
interactions at higher energies opened up with the detection of high-energy
neutrinos in IceCube, partially of astrophysical origin. Scattering off matter
inside the Earth affects the distribution of their arrival directions --- from
this, we extract the neutrino-nucleon cross section at energies from 18 TeV to
2 PeV, in four energy bins, in spite of uncertainties in the neutrino flux.
Using six years of public IceCube High-Energy Starting Events, we explicitly
show for the first time that the energy dependence of the cross section above
18 TeV agrees with the predicted softer-than-linear dependence, and reaffirm
the absence of new physics that would make the cross section rise sharply, up
to a center-of-mass energy of ~1 TeV.Comment: 5 pages main text, 5 figures, technical appendices. Matches published
versio
UHE neutrino and cosmic ray emission from GRBs: revising the models and clarifying the cosmic ray-neutrino connection
Gamma-ray bursts (GRBs) have long been held as one of the most promising
sources of ultra-high energy (UHE) neutrinos. The internal shock model of GRB
emission posits the joint production of UHE cosmic ray (UHECRs, above 10^8
GeV), photons, and neutrinos, through photohadronic interactions between source
photons and magnetically-confined energetic protons, that occur when
relativistically-expanding matter shells loaded with baryons collide with one
another. While neutrino observations by IceCube have now ruled out the simplest
version of the internal shock model, we show that a revised calculation of the
emission, together with the consideration of the full photohadronic cross
section and other particle physics effects, results in a prediction of the
prompt GRB neutrino flux that still lies one order of magnitude below the
current upper bounds, as recently exemplified by the results from ANTARES. In
addition, we show that by allowing protons to directly escape their magnetic
confinement without interacting at the source, we are able to partially
decouple the cosmic ray and prompt neutrino emission, which grants the freedom
to fit the UHECR observations while respecting the neutrino upper bounds.
Finally, we briefly present advances towards pinning down the precise relation
between UHECRs and UHE neutrinos, including the baryonic loading required to
fit UHECR observations, and we will assess the role that very large volume
neutrino telescopes play in this.Comment: 4 pages, 2 figures. To be published in Proceedings of the 6th Very
Large Volume Neutrino Telescope Workshop (VLVnT13), Stockholm, Sweden, 5-7
August, 201
Are gamma-ray bursts the sources of ultra-high energy cosmic rays?
We reconsider the possibility that gamma-ray bursts (GRBs) are the sources of
the ultra-high energy cosmic rays (UHECRs) within the internal shock model,
assuming a pure proton composition of the UHECRs. For the first time, we
combine the information from gamma-rays, cosmic rays, prompt neutrinos, and
cosmogenic neutrinos quantitatively in a joint cosmic ray production and
propagation model, and we show that the information on the cosmic energy budget
can be obtained as a consequence. In addition to the neutron model, we consider
alternative scenarios for the cosmic ray escape from the GRBs, i.e., that
cosmic rays can leak from the sources. We find that the dip model, which
describes the ankle in UHECR observations by the pair production dip, is
strongly disfavored in combination with the internal shock model because a)
unrealistically high baryonic loadings (energy in protons versus energy in
electrons/gamma-rays) are needed for the individual GRBs and b) the prompt
neutrino flux easily overshoots the corresponding neutrino bound. On the other
hand, GRBs may account for the UHECRs in the ankle transition model if cosmic
rays leak out from the source at the highest energies. In that case, we
demonstrate that future neutrino observations can efficiently test most of the
parameter space -- unless the baryonic loading is much larger than previously
anticipated.Comment: 55 pages, 23 figures, 1 table. Version accepted for publication in
Astroparticle Physics. Main analysis performed with TA data; for plots with
HiRes data, see v
Unitarity Bounds of Astrophysical Neutrinos
The flavor composition of astrophysical neutrinos observed at neutrino
telescopes is related to the initial composition at their sources via
oscillation-averaged flavor transitions. If the time evolution of the neutrino
flavor states is unitary, the probability of neutrinos changing flavor is
solely determined by the unitary mixing matrix that relates the neutrino flavor
and propagation eigenstates. In this paper we derive general bounds on the
flavor composition of TeV-PeV astrophysical neutrinos based on unitarity
constraints. These bounds are useful for studying the flavor composition of
high-energy neutrinos, where energy-dependent nonstandard flavor mixing can
dominate over the standard mixing observed in accelerator, reactor, and
atmospheric neutrino oscillations.Comment: revised manuscript published in Phys. Rev. D 98, 123023 (2018
Theoretically palatable flavor combinations of astrophysical neutrinos
The flavor composition of high-energy astrophysical neutrinos can reveal the
physics governing their production, propagation, and interaction. The IceCube
Collaboration has published the first experimental determination of the ratio
of the flux in each flavor to the total. We present, as a theoretical
counterpart, new results for the allowed ranges of flavor ratios at Earth for
arbitrary flavor ratios in the sources. Our results will allow IceCube to more
quickly identify when their data imply standard physics, a general class of new
physics with arbitrary (incoherent) combinations of mass eigenstates, or new
physics that goes beyond that, e.g., with terms that dominate the Hamiltonian
at high energy.Comment: 13 pages, 12 figures. Matches published versio
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