1,952 research outputs found
Indirect Dark Matter Searches in the Light of ATIC, FERMI, EGRET and PAMELA
Recently, new data on antiprotons and positrons from PAMELA, e- + e+ spectra
from ATIC, FERMI and HESS up to TeV energies all indicate deviations from
expectations, which has caused an interesting mix of new explanations, ranging
from background, standard astrophysical sources to signals from dark matter
(DM) annihilation. Unfortunately, the excess in positrons is not matched with
obvious excesses in antiprotons or gamma rays, so a new class of DM scenarios
with leptophilic WIMP candidates have been invoked. On the other hand, the
increase in the positron fraction, which could have had any spectral shape for
new physics, matches well the shape expected from proton background.Comment: Invited talk at SUSY09, the 17th International Conference on
Supersymmetry and the Unification of Fundamental Interactions, Boston, 200
Perspectives on the detection of supersymmetric Dark Matter
Up to now searches for Dark Matter (DM) detection have not been successful,
either because our paradigm in how DM signals should look like are wrong or the
detector sensitivity is still too low in spite of the large progress made in
recent years. We discuss both possibilities starting with what we know about DM
from cosmology and why Supersymmetry provides such an interesting paradigm for
cosmology and particle physics in order to appreciate what it means to give up
this paradigm. In addition, we compare the predicted cross sections for direct
and indirect DM detection with observations with emphasis on the latest
developments. Especially, we discuss the possible origins of the two hotly
debated candidates for a DM annihilation signal, namely the positron excess and
the Fermi GeV excess, which are unfortunately incompatible with each other and
more mundane astrophysical explanations exist.Comment: 18 pages, 12 figures. Invited talk at ICNFP2017, August 2017, Crete,
Greec
Determination of the Local Dark Matter Density in our Galaxy
The rotation curve, the total mass and the gravitational potential of the
Galaxy are sensitive measurements of the dark matter halo profile. In this
publication cuspy and cored DM halo profiles are analysed with respect to
recent astronomical constraints in order to constrain the shape of the Galactic
DM halo and the local DM density. All Galactic density components (luminous
matter and DM) are parametrized. Then the total density distribution is
constrained by astronomical observations: 1) the total mass of the Galaxy, 2)
the total matter density at the position of the Sun, 3) the surface density of
the visible matter, 4) the surface density of the total matter in the vicinity
of the Sun, 5) the rotation speed of the Sun and 6) the shape of the velocity
distribution within and above the Galactic disc. The mass model of the Galaxy
is mainly constrained by the local matter density (Oort limit), the rotation
speed of the Sun and the total mass of the Galaxy from tracer stars in the
halo. It is shown from a statistical chi^2 fit to all data that the local DM
density is strongly positively (negatively) correlated with the scale length of
the DM halo (baryonic disc). Since these scale lengths are poorly constrained
the local DM density can vary from 0.2 to 0.4 GeV/cm^3 (0.005 - 0.01
M_sun/pc^3) for a spherical DM halo profile and allowing total Galaxy masses up
to 2 * 10^12 M_sun. For oblate DM halos and dark matter discs, as predicted in
recent N-body simulations, the local DM density can be increased significantly.Comment: 10 pages, 8 figure
Becoming more systematic about flexible learning: beyond time and distance
Changes in higher education frequently involve the need for more flexibility in course design and delivery. Flexibility is a concept that can be operationalized in many ways. One approach to conceptualizing flexibility within courses is to distinguish planning-type flexibility, which the instructor can designate before the course begins and which needs to be managed when the course is offered, for interpersonal flexibility, which relates more to the dynamics of the course as it is experienced by the learners. Course management systems (CMSs) offer options that can support both of these sorts of flexibility, if instructors use the CMSs with a systematic frame of reference. The instructor faces challenges in managing both types of flexibility, but the experience at one institution shows that being systematic about flexibility choices and ways to support those choices in the institutional CMS can help in meeting these challenges
Indirect Dark Matter Signals from EGRET and PAMELA compared
Dark Matter annihilation (DMA) may yield an excess of gamma rays and
antimatter particles, like antiprotons and positrons, above the background from
cosmic ray interactions. The excess of diffuse Galactic Gamma Rays from EGRET
shows all the features expected from DMA. The new precise measurements of the
antiproton and positron fractions from PAMELA are compared with the EGRET
excess. It is shown that the charged particles are strongly dependent on the
propagation model used. The usual propagation models with isotropic propagation
models are incompatible with the recently observed convection in our Galaxy.
Convection leads to an order of magnitude uncertainty in the yield of charged
particles from DMA, since even a rather small convection will let drift the
charged particles in the halo to outer space. It is shown that such anisotropic
propagation models including convection prefer a contribution from DMA for the
antiprotons, but the rise in the positron fraction, as observed by PAMELA, is
incompatible with DMA, if compared with the EGRET excess. A rise in the
positron/electron ratio is expected, if the observed rise in the
proton/electron ratio is carefully fitted in a propagation model, although the
rise is slightly larger than expected, so additional local sources may
contribute as well within the limited accuracy of the data.Comment: 10 pages, 4 figures, Contributed paper to the Eighth UCLA Symposium:
Sources and Detection of Dark Matter and Dark Energy in the Univers
Simulation of beam induced lattice defects of diamond detectors using FLUKA
Diamond is more and more used as detector material for particle detection.
One argument for diamond is its higher radiation hardness compared to silicon.
Since various particles have different potential for radiation damage at
different energies a scaling rule is necessary for the prediction of radiation
damage. For silicon detectors the non-ionising energy loss (NIEL) is used for
scaling the effects of different particles. A different way of predicting the
radiation damage is based on the Norget-Robinson-Torrens theorem to predict the
number of displacements per atom (DPA). This provides a better scaling rule
since recombination effects are taken into account. This model is implemented
in the FLUKA Monte Carlo simulations package for protons, neutrons and pions.
We compare simulation results of NIEL and DPA for diamond and silicon material
exposed to protons, neutrons and pions for a wide range of energies
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