7,199 research outputs found
On wild ramification in quaternion extensions
Quaternion extensions are often the smallest extensions to exhibit special
properties. In the setting of the Hasse-Arf Theorem, for instance, quaternion
extensions are used to illustrate the fact that upper ramification numbers need
not be integers. These extensions play a similar role in Galois module
structure. To better understand these examples, we catalog the ramification
filtrations that are possible in totally ramified extensions of dyadic number
fields. Interestingly, we find that the catalog depends, for sharp lower
bounds, upon the refined ramification filtration, which is associated with the
biquatratic subfield. Moreover these examples, as counter-examples to the
conclusion of Hasse-Arf, occur only when the refined filtration is, in two
different ways, extreme.Comment: 19 pages. This is an extensive revision of the earlier draf
No Indications of Axion-Like Particles From Fermi
As very high energy (~100 GeV) gamma rays travel over cosmological distances,
their flux is attenuated through interactions with the extragalactic background
light. Observations of distant gamma ray sources at energies between ~200 GeV
and a few TeV by ground-based gamma ray telescopes such as HESS, however,
suggest that the universe is more transparent to very high energy photons than
had been anticipated. One possible explanation for this is the existence of
axion-like-particles (ALPs) which gamma rays can efficiently oscillate into,
enabling them to travel cosmological distances without attenuation. In this
article, we use data from the Fermi Gamma Ray Space Telescope to calculate the
spectra at 1-100 GeV of two gamma ray sources, 1ES1101-232 at redshift z=0.186
and H2356-309 at z=0.165, and use this in conjunction with the measurements of
ground-based telescopes to test the ALP hypothesis. We find that the
observations can be well-fit by an intrinsic power-law source spectrum with
indices of -1.72 and -2.1 for 1ES1101-232 and H2356-309, respectively, and that
no ALPs or other exotic physics is necessary to explain the observed degree of
attenuation.Comment: 7 pages, 4 figures. v3: Matches published version, the analysis of
H2356-309 is revised, no change in conclusion
The Nearshore Fish Fauna of Bonne Bay, a Fjord within Gros Morne National Park, Newfoundland
A standardized survey of the nearshore fish fauna of Bonne Bay, a fjord within
Gros Morne National Park in western Newfoundland, was conducted using beach seines,
gill-nets and bottom trawls during the month of June over a seven year period (2002-
2008). The survey documents the presence of 31 fish species (in 17 taxonomic families).
Sampling sites varied in benthic habitat and associated fish assemblages. Both juvenile
and adult life history stages of Atlantic cod (Gadus morhua) were present in Bonne Bay,
suggesting the presence of a local population or “bay cod stock”. Acadian redfish
(Sebastes fasciatus) live in the bay, and may be members of a genetically differentiable
population of redfish. Striped wolfish (Anarhichas lupus), a fish species protected under
Canada’s Species at Risk Act (SARA), inhabits Bonne Bay. Surrounded by Gros Morne
National Park, this bay with a diverse fish fauna is a focus of local stewardship and
conservation efforts
The Milky Way as a Kiloparsec-Scale Axionscope
Very high energy gamma-rays are expected to be absorbed by the extragalactic
background light over cosmological distances via the process of
electron-positron pair production. Recent observations of cosmologically
distant gamma-ray emitters by ground based gamma-ray telescopes have, however,
revealed a surprising degree of transparency of the universe to very high
energy photons. One possible mechanism to explain this observation is the
oscillation between photons and axion-like-particles (ALPs). Here we explore
this possibility further, focusing on photon-ALP conversion in the magnetic
fields in and around gamma-ray sources and in the magnetic field of the Milky
Way, where some fraction of the ALP flux is converted back into photons. We
show that this mechanism can be efficient in allowed regions of the ALP
parameter space, as well as in typical configurations of the Galactic Magnetic
Field. As case examples, we consider the spectrum observed from two HESS
sources: 1ES1101-232 at redshift z=0.186 and H 2356-309 at z=0.165. We also
discuss features of this scenario which could be used to distinguish it from
standard or other exotic models.Comment: 7 pages, 4 figures. Matches published versio
Satellite applications to marine geodesy
Potential use of satellites for enhancing positioning capabilities and for marine geodetic contro
The Indirect Search for Dark Matter with IceCube
We revisit the prospects for IceCube and similar kilometer-scale telescopes
to detect neutrinos produced by the annihilation of weakly interacting massive
dark matter particles (WIMPs) in the Sun. We emphasize that the astrophysics of
the problem is understood; models can be observed or, alternatively, ruled out.
In searching for a WIMP with spin-independent interactions with ordinary
matter, IceCube is only competitive with direct detection experiments if the
WIMP mass is sufficiently large. For spin-dependent interactions IceCube
already has improved the best limits on spin-dependent WIMP cross sections by
two orders of magnitude. This is largely due to the fact that models with
significant spin-dependent couplings to protons are the least constrained and,
at the same time, the most promising because of the efficient capture of WIMPs
in the Sun. We identify models where dark matter particles are beyond the reach
of any planned direct detection experiments while being within reach of
neutrino telescopes. In summary, we find that, even when contemplating recent
direct detection results, neutrino telescopes have the opportunity to play an
important as well as complementary role in the search for particle dark matter.Comment: 17 pages, 10 figures, published in the New Journal of Physics 11
105019 http://www.iop.org/EJ/abstract/1367-2630/11/10/105019, new version
submitted to correct Abstract in origina
Participation and quality of life outcomes among individuals with earthquake-related physical disability: a systematic review
Objective: A literature review to evaluate quality of life and participation outcomes of individuals with earthquake-related physical injury. Data sources: A systematic review was performed using National Health Service (NHS) Centre for Reviews and Dissemination (CRD) guidelines. MEDLINE, Embase, PsychINFO, CINAHL and AMED electronic databases were searched from 1966 to January 2014. Study selection: Studies that measured quality of life or participation outcomes among individuals who acquired a physical disability as a result of an earthquake injury were included, with no limits on research design. Data extraction: The search yielded 961 potentially relevant articles after removal of duplicates. Of these, only 8 articles met the inclusion criteria. Studies were rated for quality using the Critical Appraisal Skills Programme (CASP) guidelines. Data synthesis: A narrative synthesis was performed due to the heterogeneity of the included studies. Results: Injured earthquake survivors in developing countries experience diminished participation and reduced quality of life. Small sample sizes and lack of uniformity in outcome measurement limit generalizability. No studies from developed countries were identified. Conclusion: To maximize our understanding of quality of life and participation in injured earthquake survivors, future research should consider both the functional consequences of the injury and the environmental impact of the earthquake. The research should be based on representative samples of the injured earthquake survivors and use validated condition-specific outcome measures that are clearly defined within the publications. In addition, research should include all countries that are affected by earthquakes
Kaluza-Klein Dark Matter, Electrons and Gamma Ray Telescopes
Kaluza-Klein dark matter particles can annihilate efficiently into
electron-positron pairs, providing a discrete feature (a sharp edge) in the
cosmic spectrum at an energy equal to the particle's mass (typically
several hundred GeV to one TeV). Although this feature is probably beyond the
reach of satellite or balloon-based cosmic ray experiments (those that
distinguish the charge and mass of the primary particle), gamma ray telescopes
may provide an alternative detection method. Designed to observe very
high-energy gamma-rays, ACTs also observe the diffuse flux of electron-induced
electromagnetic showers. The GLAST satellite, designed for gamma ray astronomy,
will also observe any high energy showers (several hundred GeV and above) in
its calorimeter. We show that high-significance detections of an
electron-positron feature from Kaluza-Klein dark matter annihilations are
possible with GLAST, and also with ACTs such as HESS, VERITAS or MAGIC.Comment: 10 pages, 2 figure
Decay of High-Energy Astrophysical Neutrinos
Existing limits on the non-radiative decay of one neutrino to another plus a
massless particle (e.g., a singlet Majoron) are very weak. The best limits on
the lifetime to mass ratio come from solar neutrino observations, and are
\tau/m \agt 10^{-4} s/eV for the relevant mass eigenstate(s). For lifetimes
even several orders of magnitude longer, high-energy neutrinos from distant
astrophysical sources would decay. This would strongly alter the flavor ratios
from the expected
from oscillations alone, and should be readily visible in the near future in
detectors such as IceCube.Comment: 4 pages, 1 figure. References added. Version to appear in PR
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