2,462 research outputs found
Anisotropy vs chemical composition at ultra-high energies
This paper proposes and discusses a test of the chemical composition of
ultra-high energy cosmic rays that relies on the anisotropy patterns measured
as a function of energy. In particular, we show that if one records an
anisotropy signal produced by heavy nuclei of charge Z above an energy E_{thr},
one should record an even stronger (possibly much stronger) anisotropy at
energies >E_{thr}/Z due to the proton component that is expected to be
associated with the sources of the heavy nuclei. This conclusion remains robust
with respect to the parameters characterizing the sources and it does not
depend at all on the modelling of astrophysical magnetic fields. As a concrete
example, we apply this test to the most recent data of the Pierre Auger
Observatory. Assuming that the anisotropy reported above 55EeV is not a
statistical accident, and that no significant anisotropy has been observed at
energies <10EeV, we show that the apparent clustering toward Cen A cannot be
attributed to heavy nuclei. Similar conclusions are drawn regarding the
apparent excess correlation with nearby active galactic nuclei. We then discuss
a robust lower bound to the magnetic luminosity that a source must possess in
order to be able to accelerate particles of charge Z up to 100EeV,
L_B>10^{45}Z^{-2}erg/s. Using this bound in conjunction with the above
conclusions, we argue that the current PAO data does not support the model of
cosmic ray origin in active radio-quiet or even radio-loud galaxies. Finally,
we demonstrate that the apparent clustering in the direction of Cen A can be
explained by the contribution of the last few gamma-ray bursts or magnetars in
the host galaxy thanks to the scattering of the cosmic rays on the magnetized
lobes.Comment: 10 pages, 3 figure
Cost-Utility Analysis of Venous Thromboembolism Prophylaxis Strategies for People Undergoing Elective Total Hip and Total Knee Replacement Surgeries in the English National Health Service
Background: Major orthopedic surgery, such as elective total hip replacement (eTHR) and elective total knee replacement (eTKR), are associated with a higher risk of venous thromboembolism (VTE) than other surgical procedures. Little is known, however, about the cost-effectiveness of VTE prophylaxis strategies in people undergoing these procedures. Aim: The aim of this work was to assess the cost-effectiveness of these strategies from the English National Health Service perspective to inform NICE guideline (NG89) recommendations. Materials and Methods: Cost-utility analysis, using decision modeling, was undertaken to compare 15 VTE prophylaxis strategies for eTHR and 12 for eTKR, in addition to “no prophylaxis” strategy. The analysis complied with the NICE Reference Case. Structure and assumptions were agreed with the guideline committee. Incremental net monetary benefit (INMB) was calculated, vs. the model comparator (LMWH+ antiembolism stockings), at a threshold of £20,000/quality-adjusted life-year (QALY) gained. The model was run probabilistically. Deterministic sensitivity analyses (SAs) were undertaken to assess the robustness of the results. Results: The most cost-effective strategies were LMWH for 10 days followed by aspirin for 28 days (INMB = £530 [95% CI: -£784 to £1,103], probability of being most cost-effective = 72%) for eTHR, and foot pump (INMB = £353 [95% CI: -£101 to £665]; probability of being most cost-effective = 18%) for eTKR. There was considerable uncertainty regarding the cost-effectiveness ranking in the eTKR analysis. The results were robust to change in all SAs. Conclusions: For eTHR, LMWH (standard dose) for 10 days followed by aspirin for 28 days is the most cost-effective VTE prophylaxis strategy. For eTKR, the results are highly uncertain but foot pump appeared to be the most cost-effective strategy, followed closely by aspirin (low dose). Future research should focus on assessing cost-effectiveness of VTE prophylaxis in the eTKR population.Peer reviewe
Doubly virtual Compton scattering and the beam normal spin asymmetry
We construct an invariant basis for Compton scattering with two virtual
photons (VVCS). The basis tensors are chosen to be gauge invariant and
orthogonal to each other. The properties of the corresponding 18 invariant
amplitudes are studied in detail. We consider the special case of elastic VVCS
with the virtualities of the initial and final photons equal. The invariant
basis for VVCS in this orthogonal form does not exist in the literatur. We
furthermore use this VVCS tensor for a calculation of the beam normal spin
asymmetry in the forward kinematics. For this, we relate the invariant
amplitudes to the helicity amplitudes of the VVCS reaction. The imaginary parts
of these latter are related to the inclusive cross section by means of the
optical theorem. We use the phenomenological value of the transverse cross
section mbarn and the Callan-Gross relation which relates the
longitudinal cross section to the transverse one. The result of the
calculation agrees with an existing calculation and predicts the negative
values of the asymmetry of the order of 4-6 ppm in the energy range from
6 to 45 ppm and for very forward angles.Comment: 13 pages, 2 figures, revtex, submitted to Phys. Rev. C; new version:
two figures added, typos correcte
On the behaviour of the nuclear spectral function at high momentum and removal energy
The extrapolation of the nuclear spectral function at large nucleon
three-momentum and removal energy is suggested.Comment: 13 pages, 2 Postscript figure
Threshold features in transport through a 1D constriction
Suppression of electron current through a 1D channel of length
connecting two Fermi liquid reservoirs is studied taking into account the
Umklapp electron-electron interaction induced by a periodic potential. This
interaction causes Hubbard gaps for . In the perturbative
regime where ( charge velocity), and for small deviations
of the electron density from its commensurate values
can diverge with some exponent as voltage or temperature decreases above
, while it goes to zero below . This results
in a nonmonotonous behavior of the conductance.Comment: Final variant published in PRL, 79, 1714; minor correction
Probing Pseudo-Dirac Neutrino through Detection of Neutrino Induced Muons from GRB Neutrinos
The possibility to verify the pseudo-Dirac nature of neutrinos is
investigated here via the detection of ultra high energy neutrinos from distant
cosmological objects like GRBs. The very long baseline and the energy range
from TeV to EeV for such neutrinos invokes the likelihood to
probe very small pseude-Dirac splittings. The expected secondary muons from
such neutrinos that can be detected by a kilometer scale detector such as
ICECUBE is calculated. The pseudo-Dirac nature, if exists, will show a
considerable departure from flavour oscillation scenario in the total yield of
the secondary muons induced by such neutrinos.Comment: 11 pages, 3figure
What it takes to measure a fundamental difference between dark matter and baryons: the halo velocity anisotropy
Numerous ongoing experiments aim at detecting WIMP dark matter particles from
the galactic halo directly through WIMP-nucleon interactions. Once such a
detection is established a confirmation of the galactic origin of the signal is
needed. This requires a direction-sensitive detector. We show that such a
detector can measure the velocity anisotropy beta of the galactic halo.
Cosmological N-body simulations predict the dark matter anisotropy to be
nonzero, beta~0.2. Baryonic matter has beta=0 and therefore a detection of a
nonzero beta would be strong proof of the fundamental difference between dark
and baryonic matter. We estimate the sensitivity for various detector
configurations using Monte Carlo methods and we show that the strongest signal
is found in the relatively few high recoil energy events. Measuring beta to the
precision of ~0.03 will require detecting more than 10^4 WIMP events with
nuclear recoil energies greater than 100 keV for a WIMP mass of 100 GeV and a
32S target. This number corresponds to ~10^6 events at all energies. We discuss
variations with respect to input parameters and we show that our method is
robust to the presence of backgrounds and discuss the possible improved
sensitivity for an energy-sensitive detector.Comment: 15 pages, 8 figures, accepted by JCAP. Matches accepted versio
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