1,183 research outputs found
Bang-Bang Boosting of RRTs
This paper explores the use of time-optimal controls to improve the
performance of sampling-based kinodynamic planners. A computationally efficient
steering method is introduced that produces time-optimal trajectories between
any states for a vector of double integrators. This method is applied in three
ways: 1) to generate RRT edges that quickly solve the two-point boundary-value
problems, 2) to produce an RRT (quasi)metric for more accurate Voronoi bias,
and 3) to time-optimize a given collision-free trajectory. Experiments are
performed for state spaces with up to 2000 dimensions, resulting in improved
computed trajectories and orders of magnitude computation time improvements
over using ordinary metrics and constant controls
On the antimatter signatures of the cosmological dark matter subhalos
While the PAMELA collaboration has recently confirmed the cosmic ray positron
excess, it is interesting to review the effects of dark matter (DM) subhalos on
the predicted antimatter signals. We recall that, according to general subhalo
properties as inferred from theoretical cosmology, and for DM with constant
annihilation cross section, the enhancement cannot be 20 for the
antimatter yield. This bound is obviously different from that found for
gamma-rays. We also recall some predictions for supersymmetric benchmark models
observable at the LHC and derived in the cosmological N-body framework,
illustrating in the meantime the existing discrepancy between the profiles
derived from N-body experiments and the current observations of the Milky Way.Comment: Proceeding prepared for the "Dark Matter and Dark Energy" conference
(Lyon, France, July 2008) -- discussion a bit updated since then. 6 page
10 GeV dark matter candidates and cosmic-ray antiprotons
Recent measurements performed with some direct dark matter detection
experiments, e.g. CDMS-II and CoGENT (after DAMA/LIBRA), have unveiled a few
events compatible with weakly interacting massive particles. The preferred mass
range is around 10 GeV, with a quite large spin-independent cross section of
-. In this paper, we recall that a light dark
matter particle with dominant couplings to quarks should also generate
cosmic-ray antiprotons. Taking advantage of recent works constraining the
Galactic dark matter mass profile on the one hand and on cosmic-ray propagation
on the other hand, we point out that considering a thermal annihilation cross
section for such low mass candidates very likely results in an antiproton flux
in tension with the current data, which should be taken into account in
subsequent studies.Comment: 4 pages, 2 figures. V2: minor changes to match the published versio
Antiproton and Positron Signal Enhancement in Dark Matter Mini-Spikes Scenarios
The annihilation of dark matter (DM) in the Galaxy could produce specific
imprints on the spectra of antimatter species in Galactic cosmic rays, which
could be detected by upcoming experiments such as PAMELA and AMS02. Recent
studies show that the presence of substructures can enhance the annihilation
signal by a "boost factor" that not only depends on energy, but that is
intrinsically a statistical property of the distribution of DM substructures
inside the Milky Way. We investigate a scenario in which substructures consist
of "mini-spikes" around intermediate-mass black holes. Focusing on
primary positrons and antiprotons, we find large boost factors, up to a few
thousand, that exhibit a large variance at high energy in the case of positrons
and at low energy in the case of antiprotons. As a consequence, an estimate of
the DM particle mass based on the observed cut-off in the positron spectrum
could lead to a substantial underestimate of its actual value.Comment: 13 pages, 9 figures, minor changes, version accepted for publication
in PR
Full calculation of clumpiness boost factors for antimatter cosmic rays in the light of Lambda-CDM N-body simulation results
Anti-proton and positron Galactic cosmic ray spectra are among the key
targets for indirect detection of dark matter. The boost factors, corresponding
to an enhancement of the signal and linked to the clumpiness properties of the
dark matter distribution, have been taken as high as thousands in the past. The
dramatic impact of these boost factors for indirect detection of antiparticles,
for instance with the PAMELA satellite or the coming AMS-02 experiment, asks
for their detailed calculation. We take into account the results of high
resolution N-body dark matter simulations to calculate the most likely energy
dependent boost factors linked to the cosmic ray propagation properties, for
anti-protons and positrons. Starting from the mass and space distributions of
sub-halos, the anti-proton and positron propagators are used to calculate the
mean value and the variance of the boost factor for the primary fluxes. We take
advantage of the statistical method introduced in Lavalle et al. (2007) and
cross-check the results with Monte Carlo computations. By spanning some extreme
configurations of sub-halo and propagation properties, we find that the average
contribution of the clumps is negligible compared to that of the smooth dark
matter component. Sub-halos do not lead to enhancement of the signals, unless
they are taken with some extreme (unexpected) properties. This result is
independent of the nature of the self-annihilating dark matter candidate
considered, and provides precise estimates of the theoretical and the
statistical uncertainties of the antimatter flux from dark matter
substructures. Spectral distortions can still be expected in antimatter flux
measurements, but scenarios invoking large and even mild clumpiness boost
factors are strongly disfavoured by our analysis.Comment: Final version, matching the published one. 32 pages, 12 figure
Cosmic-ray antiproton constraints on light dark matter candidates
Some direct detection experiments have recently collected excess events that
could be interpreted as a dark matter (DM) signal, pointing to particles in the
10 GeV mass range. We show that scenarios in which DM can self-annihilate
with significant couplings to quarks are likely excluded by the cosmic-ray (CR)
antiproton data, provided the annihilation is S-wave dominated when DM
decouples in the early universe. These limits apply to most of supersymmetric
candidates, eg in the minimal supersymmetric standard model (MSSM) and in the
next-to-MSSM (NMSSM), and more generally to any thermal DM particle with
hadronizing annihilation final states.Comment: Contribution to the proceedings of TAUP-2011 (Munich, 5-9 IX 2011). 4
page
Antimatter signals of singlet scalar dark matter
We consider the singlet scalar model of dark matter and study the expected
antiproton and positron signals from dark matter annihilations. The regions of
the viable parameter space of the model that are excluded by present data are
determined, as well as those regions that will be probed by the forthcoming
experiment AMS-02. In all cases, different propagation models are investigated,
and the possible enhancement due to dark matter substructures is analyzed. We
find that the antiproton signal is more easily detectable than the positron one
over the whole parameter space. For a typical propagation model and without any
boost factor, AMS-02 will be able to probe --via antiprotons-- the singlet
model of dark matter up to masses of 600 GeV. Antiprotons constitute,
therefore, a promising signal to constraint or detect the singlet scalar model.Comment: 24 pages, 8 figures. v2: minor improvements. Accepted for publication
in JCA
Galactic secondary positron flux at the Earth
Secondary positrons are produced by spallation of cosmic rays within the
interstellar gas. Measurements have been typically expressed in terms of the
positron fraction, which exhibits an increase above 10 GeV. Many scenarios have
been proposed to explain this feature, among them some additional primary
positrons originating from dark matter annihilation in the Galaxy. The PAMELA
satellite has provided high quality data that has enabled high accuracy
statistical analyses to be made, showing that the increase in the positron
fraction extends up to about 100 GeV. It is therefore of paramount importance
to constrain theoretically the expected secondary positron flux to interpret
the observations in an accurate way. We find the secondary positron flux to be
reproduced well by the available observations, and to have theoretical
uncertainties that we quantify to be as large as about one order of magnitude.
We also discuss the positron fraction issue and find that our predictions may
be consistent with the data taken before PAMELA. For PAMELA data, we find that
an excess is probably present after considering uncertainties in the positron
flux, although its amplitude depends strongly on the assumptions made in
relation to the electron flux. By fitting the current electron data, we show
that when considering a soft electron spectrum, the amplitude of the excess
might be far lower than usually claimed. We provide fresh insights that may
help to explain the positron data with or without new physical model
ingredients. PAMELA observations and the forthcoming AMS-02 mission will allow
stronger constraints to be aplaced on the cosmic--ray transport parameters, and
are likely to reduce drastically the theoretical uncertainties.Comment: 15 pages, 12 figures. The recent PAMELA data on the positron fraction
(arXiv:0810.4995) have been included and the ensuing discussion has been
extended. Accepted version in A&
Antimatter cosmic rays from dark matter annihilation: First results from an N-body experiment
[Abridged]. We take advantage of the galaxy-like 3D dark matter map extracted
from the HORIZON Project results to calculate the positron and antiproton
fluxes from dark matter annihilation, in a model-independent approach as well
as for dark matter particle benchmarks relevant at the LHC scale (from
supersymmetric and extra-dimensional theories). Such a study is dedicated to a
better estimate of the theoretical uncertainties affecting predictions, while
the PAMELA and GLAST satellites are currently taking data which will soon
provide better observational constraints. We discuss the predictions of the
antiproton and positron fluxes, and of the positron fraction as well, as
compared to the current data. We finally discuss the limits of the Nbody
framework in describing the dark matter halo of our Galaxy.Comment: 19 pages, 9 figures. Backgrounds included and additional comments and
figures on the positron fraction. Accepted for publication in PR
On the use of the escape speed estimates in setting dark matter direct detection limits
The knowledge of the high velocity tail of the WIMP velocity distribution has a strong impact on the way direct detection (DD) may constrain or discover light WIMPs in the GeV mass range. Recently, there have been important observational efforts to estimate the so-called Galactic escape speed at the position of the Earth, for instance the analysis published in early 2014 by the RAVE Collaboration ' , which is of interest in the perspective of reducing the astrophysical uncertainties in DD. Nevertheless, these new estimates cannot be used blindly as they rely on assumptions in the dark halo modeling, which induce tight correlations between the escape speed and other local astrophysical parameters (e.g. the local circular speed and dark matter density). We make a self-consistent study of the implications of the RAVE results on DD assuming isotropic DM velocity distributions, both Maxwellian and ergodic. Taking as reference the experimental sensitivities currently achieved by LUX, CRESST2, and SuperCDMS, we show that the DD constraints on WIMPs (and associated uncertainties) are slightly stronger (moderate)
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