7,963 research outputs found
Indirect Signals from Dark Matter in Split Supersymmetry
We study the possibilities for the indirect detection of dark matter in Split
Supersymmetry from gamma-rays, positrons, and antiprotons. The most promising
signal is the gamma-ray line, which may be observable at the next generation of
detectors. For certain halo profiles and a high mass neutralino, the line can
even be visible in current experiments. The continuous gamma-ray signal may be
observable, if there is a central spike in the galactic halo density. The
signals are found to be similar to those in MSSM models. These indirect signals
complement other experiments, being most easily observable for regions of
parameter space, such as heavy wino and higgsino dominated neutralinos, which
are least accessible for direct detection and accelerator searches.Comment: 10 pages, 5 figures; experimental sensitivities added to figure 2,
revised version to appear in Phys. Rev.
A review of bovine Johne's disease control activities in 6 endemically infected countries
Mycobacterium avium subspecies paratuberculosis (MAP) is endemic in the bovine populations of many countries and can cause a significant reduction in animal welfare and production efficiency making control desirable. Effective control has proved very difficult to achieve despite multiple regionally coordinated programmes being in existence since the 1920s. The international community increasingly recognises the value in learning from the collective experiences of existing programmes to improve the effectiveness of control. The aim of this review is to outline key aspects of bovine Johne's disease control activities across 6 endemically infected countries to facilitate comparison of current international practice. The background, control activities and monitoring components of programmes in Australia, Canada, Denmark, the Netherlands, the United Kingdom and the United States of America were individually reviewed. Factual accuracy of each review was checked by individuals involved in the respective programmes before the reviews were condensed and combined into a single document presented here, with the complete reviews of each programme available as supplementary material. There was considerable heterogeneity in key aspects of control activity design including goals, responses to declining participation, herd classification, recommended control measures and associated test requirements. The data presented will be of interest to organisations that are involved in developing new or existing regionally coordinated BJD control activities
Dark Matter Searches with Astroparticle Data
The existence of dark matter (DM) was first noticed by Zwicky in the 1930s,
but its nature remains one of the great unsolved problems of physics. A variety
of observations indicate that it is non-baryonic and non-relativistic. One of
the preferred candidates for non-baryonic DM is a weakly interacting massive
particle (WIMP) that in most models is stable. WIMP self-annihilation can
produce cosmic rays, gamma rays, and other particles with signatures that may
be detectable. Hints of anomalous cosmic-ray spectra found by recent
experiments, such as PAMELA, have motivated interesting interpretations in
terms of DM annihilation and/or decay. However, these signatures also have
standard astrophysical interpretations, so additional evidence is needed in
order to make a case for detection of DM annihilation or decay. Searches by the
Fermi Large Area Telescope for gamma-ray signals from clumps, nearby dwarf
spheroidal galaxies, and galaxy clusters have also been performed, along with
measurements of the diffuse Galactic and extragalactic gamma-ray emission. In
addition, imaging atmospheric Cherenkov telescopes like HESS, MAGIC, and
VERITAS have reported on searches for gamma-ray emission from dwarf galaxies.
In this review, we examine the status of searches for particle DM by these
instruments and discuss the interpretations and resulting DM limits.Comment: Solicited review article to appear in Annual Reviews of Astronomy and
Astrophysics. 52 pages, 10 figures (higher resolution figures will appear in
the journal article
New Measurements with Stopped Particles at the LHC
Metastable particles are common in many models of new physics at the TeV
scale. If charged or colored, a reasonable fraction of all such particles
produced at the LHC will stop in the detectors and give observable out of time
decays. We demonstrate that significant information may be learned from such
decays about the properties (e.g. charge or spin) of this particle and of any
other particles to which it decays, for example a dark matter candidate. We
discuss strategies for measuring the type of decay (two- vs three-body), the
types of particles produced, and the angular distribution of the produced
particles using the LHC detectors. We demonstrate that with O(10-100) observed
decay events, not only can the properties of the new particles be measured but
indeed even the Lorentz structure of the decay operator can be distinguished in
the case of three-body decays. These measurements can not only reveal the
correct model of new physics at the TeV scale, but also give information on
physics giving rise to the decay at energy scales far above those the LHC can
probe directly.Comment: 31 pages, 6 figures. References added, updated to reflect recent
experimental results, version accepted for publication in Physical Review
Coarse-grained simulations of flow-induced nucleation in semi-crystalline polymers
We perform kinetic Monte Carlo simulations of flow-induced nucleation in
polymer melts with an algorithm that is tractable even at low undercooling. The
configuration of the non-crystallized chains under flow is computed with a
recent non-linear tube model. Our simulations predict both enhanced nucleation
and the growth of shish-like elongated nuclei for sufficiently fast flows. The
simulations predict several experimental phenomena and theoretically justify a
previously empirical result for the flow-enhanced nucleation rate. The
simulations are highly pertinent to both the fundamental understanding and
process modeling of flow-induced crystallization in polymer melts.Comment: 17 pages, 6 eps figure
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