2,147 research outputs found
Fermionic WIMPs and Vacuum Stability in the Scotogenic Model
We demonstrate that the condition of vacuum stability severely restricts
scenarios with fermionic WIMP dark matter in the scotogenic model. The sizable
Yukawa couplings that are required to satisfy the dark matter constraint via
thermal freeze-out in these scenarios tend to destabilise the vacuum at scales
below that of the heaviest singlet fermion, rendering the model inconsistent
from a theoretical point of view. By means of a scan over the parameter space,
we study the impact of these renormalisation group effects on the viable
regions of this model. Our analysis shows that a fraction of more than 90% of
the points compatible with all known experimental constraints - including
neutrino masses, the dark matter density, and lepton flavour violation - is
actually inconsistent.Comment: 8 pages, 6 figures; content matches published versio
Theory of a resonantly interacting impurity in a Bose-Einstein condensate
We investigate a Bose-Einstein condensate in strong interaction with a single
impurity particle. While this situation has received considerable interest in
recent years, the regime of strong coupling remained inaccessible to most
approaches due to an instability in Bogoliubov theory arising near the
resonance. We present a nonlocal extension of Gross-Pitaevskii theory that is
free of such divergences and does not require the use of the Born approximation
in any of the interaction potentials. We find a new dynamical transition regime
between attractive and repulsive polarons, where an interaction quench results
in a finite number of coherent oscillations in the density profiles of the
medium and in the contact parameter before equilibrium is reached.Comment: 6 pages, 3 figures; published versio
A new method for an objective, -based spectroscopic analysis of early-type stars
A precise quantitative spectral analysis - encompassing atmospheric parameter
and chemical elemental abundance determination - is time consuming due to its
iterative nature and the multi-parameter space to be explored, especially when
done "by eye". A robust automated fitting technique that is as trustworthy as
traditional methods would allow for large samples of stars to be analyzed in a
consistent manner in reasonable time. We present a semi-automated quantitative
spectral analysis technique for early-type stars based on the concept of
minimization. The method's main features are: far less subjective than
typical "by eye" methods, correction for inaccurate continuum normalization,
consideration of the whole useful spectral range, simultaneous sampling of the
entire multi-parameter space (effective temperature, surface gravity,
microturbulence, macroturbulence, projected rotational velocity, radial
velocity, elemental abundances) to find the global best solution, applicable
also to composite spectra. The method is fast, robust and reliable as seen from
formal tests and from a comparison with previous analyses. Consistent
quantitative spectral analyses of large samples of early-type stars can be
performed quickly with very high accuracy.Comment: 32 pages, 4 figures, Astronomy and Astrophysics, accepte
Multi-Satellite Observations of Cygnus X-1 to Study the Focused Wind and Absorption Dips
High-mass X-ray binary systems are powered by the stellar wind of their donor
stars. The X-ray state of Cygnus X-1 is correlated with the properties of the
wind which defines the environment of mass accretion. Chandra-HETGS
observations close to orbital phase 0 allow for an analysis of the photoionzed
stellar wind at high resolution, but because of the strong variability due to
soft X-ray absorption dips, simultaneous multi-satellite observations are
required to track and understand the continuum, too. Besides an earlier joint
Chandra and RXTE observation, we present first results from a recent campaign
which represents the best broad-band spectrum of Cyg X-1 ever achieved: On 2008
April 18/19 we observed this source with XMM-Newton, Chandra, Suzaku, RXTE,
INTEGRAL, Swift, and AGILE in X- and gamma-rays, as well as with VLA in the
radio. After superior conjunction of the black hole, we detect soft X-ray
absorption dips likely due to clumps in the focused wind covering >95 % of the
X-ray source, with column densities likely to be of several 10^23 cm^-2, which
also affect photon energies above 20 keV via Compton scattering.Comment: 10 pages, contributed talk at the 7th Microquasar Workshop, Foca,
Turkey, Sept. 1-5, 200
Managing the Inner Workings of Collective Intelligence Approaches for Wicked Problems – An Assessment Model and Evaluation
Ill-defined and complex problems that affect multiple stakeholders with potentially conflicting perspectives are often referred to as wicked problems. The utilization of collective intelligence (CI) via web-based platforms is a promising approach for addressing such wicked problems. The management of these information systems would benefit from evidence-based decision support regarding facilitation and improvement efforts. However, to date, there is no suitable model to guide such efforts. Existing approaches address specific applications or cover certain assessment areas but do not provide a holistic perspective. Meanwhile, research offers substantial insights into best practices for addressing wicked problems and running CI applications. This paper develops an assessment model comprising five central success dimensions for information systems that address wicked problems. Their subdimensions and associated measurement metrics allow for evidence-driven facilitation and improvement of CI applications for wicked problems. Apart from the model’s capability to improve future runs and processes, it also offers the potential to provide immediate insights for facilitation efforts during runtime. The model was validated with a platform dealing with the assessment of risks presented by global climate change. This evaluation generated strong evidence for the model’s applicability and usefulness
BK viremia in critically ill surgical patients with hemorrhagic or septic shock
<p>Abstract</p> <p>Background</p> <p>Infections with polyomavirus BK virus (BKV) are a common cause of renal dysfunction after renal transplantation and may also be harmful in surgical patients with shock. The aim of the present study was to determine the frequency of BKV viremia in critically ill surgical patients with septic or hemorrhagic shock, and, if viremia is detectable, whether viremia may be associated with renal dysfunction.</p> <p>Findings</p> <p>A total of 125 plasma samples from 44 critically ill surgical patients with septic or hemorrhagic shock were tested by real-time polymerase chain reaction (PCR) for BKV DNA during their stay on the intensive care unit (ICU). BKV viremia occurred in four patients, i.e. in three of the septic and in one of the hemorrhagic shock group. There was no association between viremia and renal dysfunction. All positive samples contained a low viral load (< 500 copies/ml).</p> <p>Conclusions</p> <p>Since BK viremia was rarely found and with low viral load only in critically ill surgical patients with shock, it is very unlikely that BK viremia results in BK nephropathy later on.</p
Coherent phonon-magnon interactions detected by micro-focused Brillouin light scattering spectroscopy
We investigated the interaction of surface acoustic waves and spin waves with
spatial resolution by micro-focused Brillouin light scattering spectroscopy in
a CoFeB ferromagnetic layer on a LiNbO-piezoelectric
substrate. We experimentally demonstrate that the magnetoelastic excitation of
magnons by phonons is coherent by studying the interfering BLS-signals of the
phonons and magnons during their conversion process.We find a pronounced
spatial dependence of the phonon annihilation and magnon excitation which we
map as a function of the magnetic field. The coupling efficiency of the surface
acoustic waves (SAWs) and the spin waves (SWs) is characterized by a magnetic
field dependent decay of the SAWs amplitude
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