1,283 research outputs found
Spectral cutoffs in indirect dark matter searches
Indirect searches for dark matter annihilation or decay products in the
cosmic-ray spectrum are plagued by the question of how to disentangle a dark
matter signal from the omnipresent astrophysical background. One of the
practically background-free smoking-gun signatures for dark matter would be the
observation of a sharp cutoff or a pronounced bump in the gamma-ray energy
spectrum. Such features are generically produced in many dark matter models by
internal Bremsstrahlung, and they can be treated in a similar manner as the
traditionally looked-for gamma-ray lines. Here, we discuss prospects for seeing
such features with present and future Atmospheric Cherenkov Telescopes.Comment: 4 pages, 2 figures, 1 table; conference proceedings for TAUP 2011,
Munich 5-9 Se
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
Constraints on small-scale cosmological perturbations from gamma-ray searches for dark matter
Events like inflation or phase transitions can produce large density
perturbations on very small scales in the early Universe. Probes of small
scales are therefore useful for e.g. discriminating between inflationary
models. Until recently, the only such constraint came from non-observation of
primordial black holes (PBHs), associated with the largest perturbations.
Moderate-amplitude perturbations can collapse shortly after matter-radiation
equality to form ultracompact minihalos (UCMHs) of dark matter, in far greater
abundance than PBHs. If dark matter self-annihilates, UCMHs become excellent
targets for indirect detection. Here we discuss the gamma-ray fluxes expected
from UCMHs, the prospects of observing them with gamma-ray telescopes, and
limits upon the primordial power spectrum derived from their non-observation by
the Fermi Large Area Space Telescope.Comment: 4 pages, 3 figures. To appear in J Phys Conf Series (Proceedings of
TAUP 2011, Munich
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
Electroweak lights from Dark Matter annihilations
The energy spectra of Standard Model particles originated from Dark Matter
annihilations can be significantly altered by the inclusion of electroweak
gauge boson radiation from the final state. A situation where this effect is
particularly important is when a Majorana Dark Matter particle annihilates into
two light fermions. This process is in p-wave and hence suppressed by the small
value of the relative velocity of the annihilating particles. The inclusion of
electroweak radiation eludes this suppression and opens up a potentially
sizeable s-wave contribution to the annihilation cross section. I will discuss
the impact of this effect on the fluxes of stable particles resulting from the
Dark Matter annihilations, which are relevant for Dark Matter indirect
searches.Comment: 4 pages, 2 figures. Contribution to the conference proceedings of
TAUP 2011, Munich - Germany (5-9 September 2011
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
Maximum Volume Subset Selection for Anchored Boxes
Let B be a set of n axis-parallel boxes in d-dimensions such that each box has a corner at the origin and the other corner in the positive quadrant, and let k be a positive integer. We study the problem of selecting k boxes in B that maximize the volume of the union of the selected boxes. The 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 algorithms in any dimension d>2 enumerate all size-k subsets. We show that:
* The problem is NP-hard already in 3 dimensions.
* In 3 dimensions, we break the enumeration of all size-k subsets, by providing an n^O(sqrt(k)) algorithm.
* For any constant dimension d, we give an efficient polynomial-time approximation scheme
Disentangling Instrumental Features of the 130 GeV Fermi Line
We study the instrumental features of photons from the peak observed at
GeV in the spectrum of Fermi-LAT data. We use the {\sc sPlots}
algorithm to reconstruct -- seperately for the photons in the peak and for
background photons -- the distributions of incident angles, the recorded time,
features of the spacecraft position, the zenith angles, the conversion type and
details of the energy and direction reconstruction. The presence of a striking
feature or cluster in such a variable would suggest an instrumental cause for
the peak. In the publically available data, we find several suggestive features
which may inform further studies by instrumental experts, though the size of
the signal sample is too small to draw statistically significant conclusions.Comment: 9 pages, 22 figures; this version includes additional variables,
study of stat sensitivity, and modification to the chi-sq calculatio
Cosmological constraints on dark matter models with velocity-dependent annihilation cross section
We derive cosmological constraints on the annihilation cross section of dark
matter with velocity-dependent structure, motivated by annihilating dark matter
models through Sommerfeld or Breit-Wigner enhancement mechanisms. In models
with annihilation cross section increasing with decreasing dark matter
velocity, big-bang nucleosynthesis and cosmic microwave background give
stringent constraints.Comment: 23 pages, 9 figures; Added reference
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