1,337 research outputs found
Aspects of production and kinetic decoupling of non-thermal dark matter
We reconsider non-thermal production of WIMP dark matter in a systematic way
and using a numerical code for accurate computations of dark matter relic
densities. Candidates with large pair annihilation rates are favored,
suggesting a connection with the anomalies in the lepton cosmic-ray flux
detected by Pamela and Fermi. Focussing on supersymmetric models we will
consider the impact of non-thermal production on the preferred mass scale for
dark matter neutralinos. We have also developed a new formalism to solve the
Boltzmann's equation for a system of coannihilating species without assuming
kinetic equilibrium and applied it to the case of pure Winos.Comment: Proceedings for the conference TAUP 201
The galactic antiproton spectrum at high energies: background expectation vs. exotic contributions
A new generation of upcoming space-based experiments will soon start to probe
the spectrum of cosmic ray antiparticles with an unprecedented accuracy and, in
particular, will open up a window to energies much higher than those accessible
so far. It is thus timely to carefully investigate the expected antiparticle
fluxes at high energies. Here, we perform such an analysis for the case of
antiprotons. We consider both standard sources as the collision of other cosmic
rays with interstellar matter, as well as exotic contributions from dark matter
annihilations in the galactic halo. Up to energies well above 100 GeV, we find
that the background flux in antiprotons is almost uniquely determined by the
existing low-energy data on various cosmic ray species; for even higher
energies, however, the uncertainties in the parameters of the underlying
propagation model eventually become significant. We also show that if the dark
matter is composed of particles with masses at the TeV scale, which is
naturally expected in extra-dimensional models as well as in certain parameter
regions of supersymmetric models, the annihilation flux can become comparable
to - or even dominate - the antiproton background at the high energies
considered here.Comment: 17 pages revtex4, 7 figures; minor changes (to match the published
version
Inflation in Gauged 6D Supergravity
In this note we demonstrate that chaotic inflation can naturally be realized
in the context of an anomaly free minimal gauged supergravity in D=6 which has
recently been the focus of some attention. This particular model has a unique
maximally symmetric ground state solution, which leaves
half of the six-dimensional supersymmetries unbroken. In this model, the
inflaton field originates from the complex scalar fields in the D=6
scalar hypermultiplet. The mass and the self couplings of the scalar field are
dictated by the D=6 Lagrangian. The scalar potential has an absolute munimum at
with no undetermined moduli fields. Imposing a mild bound on the
radius of enables us to obtain chaotic inflation. The low eenrgy
equations of motion are shown to be consistent for the range of scalar field
values relevant for inflation.Comment: one reference adde
Multi-objective optimisation of machine tool error mapping using automated planning
Error mapping of machine tools is a multi-measurement task that is planned based on expert knowledge. There are no intelligent tools aiding the production of optimal measurement plans. In previous work, a method of intelligently constructing measurement plans demonstrated that it is feasible to optimise the plans either to reduce machine tool downtime or the estimated uncertainty of measurement due to the plan schedule. However, production scheduling and a continuously changing environment can impose conflicting constraints on downtime and the uncertainty of measurement. In this paper, the use of the produced measurement model to minimise machine tool downtime, the uncertainty of measurement and the arithmetic mean of both is investigated and discussed through the use of twelve different error mapping instances. The multi-objective search plans on average have a 3% reduction in the time metric when compared to the downtime of the uncertainty optimised plan and a 23% improvement in estimated uncertainty of measurement metric when compared to the uncertainty of the temporally optimised plan. Further experiments on a High Performance Computing (HPC) architecture demonstrated that there is on average a 3% improvement in optimality when compared with the experiments performed on the PC architecture. This demonstrates that even though a 4% improvement is beneficial, in most applications a standard PC architecture will result in valid error mapping plan
Maximum Volume Subset Selection for Anchored Boxes
Let be a set of axis-parallel boxes in such that each box has a corner at the origin and the other corner in the positive quadrant of , and let be a positive integer. We study the problem of selecting boxes in that maximize the volume of the union of the selected boxes. This research is motivated by applications in skyline queries for databases and in multicriteria optimization, where the problem is known as the hypervolume subset selection problem. It is known that the problem can be solved in polynomial time in the plane, while the best known running time in any dimension is . We show that: - The problem is NP-hard already in 3 dimensions. - In 3 dimensions, we break the bound , by providing an algorithm. - For any constant dimension , we present an efficient polynomial-time approximation scheme
New Gamma-Ray Contributions to Supersymmetric Dark Matter Annihilation
We compute the electromagnetic radiative corrections to all leading
annihilation processes which may occur in the Galactic dark matter halo, for
dark matter in the framework of supersymmetric extensions of the Standard Model
(MSSM and mSUGRA), and present the results of scans over the parameter space
that is consistent with present observational bounds on the dark matter density
of the Universe. Although these processes have previously been considered in
some special cases by various authors, our new general analysis shows novel
interesting results with large corrections that may be of importance, e.g., for
searches at the soon to be launched GLAST gamma-ray space telescope. In
particular, it is pointed out that regions of parameter space where there is a
near degeneracy between the dark matter neutralino and the tau sleptons,
radiative corrections may boost the gamma-ray yield by up to three or four
orders of magnitude, even for neutralino masses considerably below the TeV
scale, and will enhance the very characteristic signature of dark matter
annihilations, namely a sharp step at the mass of the dark matter particle.
Since this is a particularly interesting region for more constrained mSUGRA
models of supersymmetry, we use an extensive scan over this parameter space to
verify the significance of our findings. We also re-visit the direct
annihilation of neutralinos into photons and point out that, for a considerable
part of the parameter space, internal bremsstrahlung is more important for
indirect dark matter searches than line signals.Comment: Replaced Fig. 2c which by mistake displayed the same spectrum as Fig.
2d; the radiative corrections reported here are now implemented in DarkSUSY
which is available at http://www.physto.se/~edsjo/darksusy
Hardness of Approximation in {P} via Short Cycle Removal: {C}ycle Detection, Distance Oracles, and Beyond
Probabilistic Analysis of Optimization Problems on Generalized Random Shortest Path Metrics
Simple heuristics often show a remarkable performance in practice for
optimization problems. Worst-case analysis often falls short of explaining this
performance. Because of this, "beyond worst-case analysis" of algorithms has
recently gained a lot of attention, including probabilistic analysis of
algorithms.
The instances of many optimization problems are essentially a discrete metric
space. Probabilistic analysis for such metric optimization problems has
nevertheless mostly been conducted on instances drawn from Euclidean space,
which provides a structure that is usually heavily exploited in the analysis.
However, most instances from practice are not Euclidean. Little work has been
done on metric instances drawn from other, more realistic, distributions. Some
initial results have been obtained by Bringmann et al. (Algorithmica, 2013),
who have used random shortest path metrics on complete graphs to analyze
heuristics.
The goal of this paper is to generalize these findings to non-complete
graphs, especially Erd\H{o}s-R\'enyi random graphs. A random shortest path
metric is constructed by drawing independent random edge weights for each edge
in the graph and setting the distance between every pair of vertices to the
length of a shortest path between them with respect to the drawn weights. For
such instances, we prove that the greedy heuristic for the minimum distance
maximum matching problem, the nearest neighbor and insertion heuristics for the
traveling salesman problem, and a trivial heuristic for the -median problem
all achieve a constant expected approximation ratio. Additionally, we show a
polynomial upper bound for the expected number of iterations of the 2-opt
heuristic for the traveling salesman problem.Comment: An extended abstract appeared in the proceedings of WALCOM 201
Neutrino signals from electroweak bremsstrahlung in solar WIMP annihilation
Bremsstrahlung of and gauge bosons, or photons, can be an important
dark matter annihilation channel. In many popular models in which the
annihilation to a pair of light fermions is helicity suppressed, these
bremsstrahlung processes can lift the suppression and thus become the dominant
annihilation channels. The resulting dark matter annihilation products contain
a large, energetic, neutrino component. We consider solar WIMP annihilation in
the case where electroweak bremsstrahlung dominates, and calculate the
resulting neutrino spectra. The flux consists of primary neutrinos produced in
processes such as and , and secondary neutrinos produced via the decays of gauge
bosons and charged leptons. After dealing with the neutrino propagation and
flavour evolution in the Sun, we consider the prospects for detection in
neutrino experiments on Earth. By comparing our signal with that for
annihilation to , we show that the detection prospects for the
bremsstrahlung annihilation channel are favourable.Comment: 18 pages, 5 figures. Discussion expanded; matches published versio
Codon adaptation-based control of protein expression in C. elegans.
We present a method to control protein levels under native genetic regulation in Caenorhabditis elegans by using synthetic genes with adapted codons. We found that the force acting on the spindle in C. elegans embryos was related to the amount of the G-protein regulator GPR-1/2. Codon-adapted versions of any C. elegans gene can be designed using our web tool, C. elegans codon adapter
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