836 research outputs found
Status report of the ANTARES project
The ANTARES project aims at the construction of an underwater neutrino
telescope at the scale of 0.1 km^2 2400 m deep in the Mediterranean Sea. After
a 4-year R&D program, the ANTARES project has entered the construction phase
which will be concluded by the end of 2004. The current status of the project
is reported.Comment: 3 pages, 2 figures. to appear in Proc. of TAUP2001 conference,
Laboratori Nazionali del Gran Sasso, Sept. 200
Testing Lorentz Invariance with Neutrinos from Ultrahigh Energy Cosmic Ray Interactions
We have previously shown that a very small amount of Lorentz invariance
violation (LIV), which suppresses photomeson interactions of ultrahigh energy
cosmic rays (UHECRs) with cosmic background radiation (CBR) photons, can
produce a spectrum of cosmic rays that is consistent with that currently
observed by the Pierre Auger Observatory (PAO) and HiRes experiments. Here, we
calculate the corresponding flux of high energy neutrinos generated by the
propagation of UHECR protons through the CBR in the presence of LIV. We find
that LIV produces a reduction in the flux of the highest energy neutrinos and a
reduction in the energy of the peak of the neutrino energy flux spectrum, both
depending on the strength of the LIV. Thus, observations of the UHE neutrino
spectrum provide a clear test for the existence and amount of LIV at the
highest energies. We further discuss the ability of current and future proposed
detectors make such observations.Comment: final version to appear in Astroparticle Physic
Lorentz Invariance Violation and the Observed Spectrum of Ultrahigh Energy Cosmic Rays
There has been much interest in possible violations of Lorentz invariance,
particularly motivated by quantum gravity theories. It has been suggested that
a small amount of Lorentz invariance violation (LIV) could turn off photomeson
interactions of ultrahigh energy cosmic rays (UHECRs) with photons of the
cosmic background radiation and thereby eliminate the resulting sharp
steepening in the spectrum of the highest energy CRs predicted by Greisen
Zatsepin and Kuzmin (GZK). Recent measurements of the UHECR spectrum reported
by the HiRes and Auger collaborations, however, indicate the presence of the
GZK effect. We present the results of a detailed calculation of the
modification of the UHECR spectrum caused by LIV using the formalism of Coleman
and Glashow. We then compare these results with the experimental UHECR data
from Auger and HiRes. Based on these data, we find a best fit amount of LIV of
,consistent with an upper limit of . This possible amount of LIV can lead to a recovery of the cosmic ray
spectrum at higher energies than presently observed. Such an LIV recovery
effect can be tested observationally using future detectors.Comment: corrected proof version to be published in Astroparticle Physic
Is the Universe More Transparent to Gamma Rays Than Previously Thought?
The MAGIC collaboration has recently reported the detection of the strong
gamma-ray blazar 3C279 during a 1-2 day flare. They have used their spectral
observations to draw conclusions regarding upper limits on the opacity of the
Universe to high energy gamma-rays and, by implication, upper limits on the
extragalactic mid-infrared background radiation. In this paper we examine the
effect of gamma-ray absorption by the extragalactic infrared radiation on
intrinsic spectra for this blazar and compare our results with the
observational data on 3C279. We find agreement with our previous results,
contrary to the recent assertion of the MAGIC group that the Universe is more
transparent to \gray s than our calculations indicate. Our analysis indicates
that in the energy range between ~80 and ~500 GeV, 3C279 has a best-fit
intrinsic spectrum with a spectral index ~1.78 using our fast evolution model
and ~2.19 using our baseline model. However, we also find that spectral indices
in the range of 0.0 to 3.0 are almost as equally acceptable as the best fit
spectral indices. Assuming the same intrinsic spectral index for this flare as
for the 1991 flare from 3C279 observed by EGRET, viz., 2.02, which lies between
our best fit indices, we estimate that the MAGIC flare was ~3 times brighter
than the EGRET flare observed 15 years earlier.Comment: version accepted for publication in ApJ Letter
High energy neutrino absorption and its effects on stars in close X-ray binaries
The physics and astrophysics of high energy neutrino production and interactions in close X-ray binary systems are studied. These studies were stimulated by recent observations of ultrahigh energy gamma-rays and possibly other ultrahigh energy particles coming from the directions of Cygnus X-3 and other binary systems and possessing the periodicity characteristics of these systems. Systems in which a compact object, such as a neutron star, is a strong source of high energy particles which, in turn, produce photons, neutronos and other secondary particles by interactions in the atmosphere of the companion star were considered. The highest energy neutrinos are absorbed deep in the companion and the associated energy deposition may be large enough to effect its structure or lead to its ultimate disruption. This neutrino heating was evaluated, starting with a detailed numerical calculation of the hadronic cascade induced in the atmosphere of the companion star. For some theoretical models, the resulting energy deposition from neutrino absorption may be so great as to disrupt the companion star over an astronomically small timescale of the order of 10,000 years. Even if the energy deposition is smaller, it may still be high enough to alter the system substantially, perhaps leading to quenching of high energy signals from the source. Given the cosmic ray luminosities required to produce the observed gamma rays from cygnus X-3 and LMX X-4, such a situation may occur in these sources
Testing Relativity at High Energies Using Spaceborne Detectors
(ABRIDGED) The Gamma-ray Large Area Space Telescope (GLAST) will measure the
spectra of distant extragalactic sources of high energy gamma-rays. GLAST can
look for energy dependent propagation effects from such sources as a signal of
Lorentz invariance violation (LIV). Such sources should also exhibit high
energy spectral cutoffs from pair production interactions with low energy
photons. The properties of such cutoffs can also be used to test LIV. Detectors
to measure gamma-ray polarization can look for the depolarizing effect of
space-time birefingence predicted by loop quantum gravity. A spaceborne
detector array looking down on Earth to study extensive air showers produced by
ultrahigh energy cosmic rays can study their spectral properties and look for a
possible deviation from the predicted GZK effect as another signal of LIV.Comment: 14 pages, Text of invitated talk presented at the "From Quantum to
Cosmos: Fundamental Physics Studies from Space" meeting. More references
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Corrected Table for the Parametric Coefficients for the Optical Depth of the Universe to Gamma-rays at Various Redshifts
Table 1 in our paper, ApJ 648, 774 (2006) entitled "Intergalactic Photon
Spectra from the Far IR to the UV Lyman Limit for 0 < z < 6 and the Optical
Depth of the Universe to High Energy Gamma-Rays" had erroneous numbers for the
coefficients fitting the parametric form for the optical depth of the universe
to gamma-rays. The correct values for these parameters as described in the
original text are given here in a corrected table for various redshifts for the
baseline model (upper row) and fast evolution (lower row) for each individual
redshift. The parametric approximation is good for optical depths between 0.01
and 100 and for gamma-ray energies up to ~2 TeV for all redshifts but also for
energies up to ~10 TeV for redshifts less than 1.Comment: Table 1 corrected and new gamma-ray energy range of validity give
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