2,867 research outputs found
Decaying dark matter: a stacking analysis of galaxy clusters to improve on current limits
We show that a stacking approach to galaxy clusters can improve current
limits on decaying dark matter by a factor , with respect to a
single source analysis, for all-sky instruments such as Fermi-LAT. Based on the
largest sample of X-ray-selected galaxy clusters available to date (the MCXC
meta-catalogue), we provide all the astrophysical information, in particular
the astrophysical term for decaying dark matter, required to perform an
analysis with current instruments.Comment: 6 pages, 3 figures, supplementary file available on demand, accepted
for publication in PR
Spallation dominated propagation of Heavy Cosmic Rays and the Local Interstellar Medium (LISM)
Measurements of ultra heavy nuclei at GeV/n energies in the galactic cosmic
radiation address the question of the sources (nucleosynthetic s- and
r-processes). As such, the determination of CR source abundances is a promising
way to discriminate between existing nucleosynthesis models. For primary
species (nuclei present and accelerated at sources), it is generally assumed
that the relative propagated abundances, if they are close in mass, are not too
different from their relative source abundances. Besides, the range of the
correction factor associated to propagation has been estimated in weighted slab
models only. Heavy CRs that are detected near Earth were accelerated from
regions that are closer to us than were the light nuclei. Hence, the geometry
of sources in the Solar neighbourhood, and as equally important, the geometry
of gas in the same region, must be taken into account. In this paper, a two
zone diffusion model is used, and as was previously investigated for
radioactive species, we report here on the impact of the local interstellar
medium (LISM) feature (under-dense medium over a scale ~100 pc) on primary and
secondary stable nuclei propagated abundances. Going down to Fe nuclei, the
connection between heavy and light abundances is also inspected. A general
trend is found that decreases the UHCR source abundances relative to the HCR
ones. This could have an impact on the level of r-process required to reproduce
the data.Comment: 12 pages, 9 figures, accepted by A&A. Comparison with truncated
weighted slab and discussion added. Figure 8 modified. New appendix on
truncated weighted slab techniqu
The effect of rotation and tidal heating on the thermal lightcurves of Super Mercuries
Short period (<50 days) low-mass (<10Mearth) exoplanets are abundant and the
few of them whose radius and mass have been measured already reveal a diversity
in composition. Some of these exoplanets are found on eccentric orbits and are
subjected to strong tides affecting their rotation and resulting in significant
tidal heating. Within this population, some planets are likely to be depleted
in volatiles and have no atmosphere. We model the thermal emission of these
"Super Mercuries" to study the signatures of rotation and tidal dissipation on
their infrared light curve. We compute the time-dependent temperature map at
the surface and in the subsurface of the planet and the resulting
disk-integrated emission spectrum received by a distant observer for any
observation geometry. We calculate the illumination of the planetary surface
for any Keplerian orbit and rotation. We include the internal tidal heat flow,
vertical heat diffusion in the subsurface and generate synthetic light curves.
We show that the different rotation periods predicted by tidal models
(spin-orbit resonances, pseudo-synchronization) produce different photometric
signatures, which are observable provided that the thermal inertia of the
surface is high, like that of solid or melted rocks (but not regolith). Tidal
dissipation can also directly affect the light curves and make the inference of
the rotation more difficult or easier depending on the existence of hot spots
on the surface. Infrared light curve measurement with the James Webb Space
Telescope and EChO can be used to infer exoplanets' rotation periods and
dissipation rates and thus to test tidal models. This data will also constrain
the nature of the (sub)surface by constraining the thermal inertia.Comment: 15 pages, 13 figures, accepted for publication in Astronomy &
Astrophysic
Heavy Nuclei Enrichment of the Galactic Cosmic Rays at High Energy: Astrophysical Interpretation
A substantial increase of the mean logarithmic mass of galactic
cosmic rays {\em vs} energy has been observed . We study three effects that
could explain this trend i) different source spectra for protons and heavy
nuclei ii) a selective nuclear destruction in flight of heavies iii) a gradient
of the source number and chemical composition in the galactic disk.
We take advantage of the diffusive cosmic ray propagation model developed at
LAPTH to study specifically the geometrical aspects of the propagation and
extend it to high energy. Using a simple modeling of the spectral knee around
$10^{15}$ eV, a bump in appears. This feature is smoother when the
spectral index of protons is steeper than Fe's.
We analyze the effects of the rigidity dependence of the diffusion
coefficient and the scale height of the confinement halo and we show that is most sensitive to the first parameter. Pure geometrical effects are less
determining than the diffusion coefficient spectral index. Subsequently, we
conclude that the physics of cosmic ray confinement is the essential cause of
the heavy nuclei enrichment until eV.Comment: 26 pages, 7 PostScript figures. Astropart. Phys, accepted; misprint
in fig6 correcte
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
Characterisation of aged HDPE pipes from drinking water distribution : investigation of crack depth by Nol ring tests under creep loading
International audienceHDPE pipes are used for the transport of drinking water. However, disinfectants in waterseem to have a strong impact on their mechanical behaviour, limiting their lifetime inoperation. Indeed, oxidation occurs when they are in contact with disinfectants leading to theformation of a thin oxidised layer coupled to the cracks initiation of cracks of different lengthsfrom the inner wall surface. An original method is proposed here to characterise the ageingeffect of the pipe mechanical behaviour. Inspired from the ASTM D 2290-04 standard, NolRing tests have been performed under tensile and creep loadings on smooth rings. Aconstitutive equation has been determined from these tests using a finite element (FE)modelling. FE simulations have been performed to study the influence of the thin oxidised PElayer. Precracked specimens with different crack depth ratio have also been modelled. Thecrack depth ratio is an important parameter to quantify pipe ageing
Dark matter annihilation and decay profiles for the Reticulum II dwarf spheroidal galaxy
The dwarf spheroidal galaxies (dSph) of the Milky Way are among the most
attractive targets for indirect searches of dark matter. In this work, we
reconstruct the dark matter annihilation (J-factor) and decay profiles for the
newly discovered dSph Reticulum II. Using an optimized spherical Jeans analysis
of kinematic data obtained from the Michigan/Magellan Fiber System (M2FS), we
find Reticulum II's J-factor to be among the largest of any Milky Way dSph. We
have checked the robustness of this result against several ingredients of the
analysis. Unless it suffers from tidal disruption or significant inflation of
its velocity dispersion from binary stars, Reticulum II may provide a unique
window on dark matter particle properties.Comment: 5 pages, 4 figures. Match the ApJL accepted versio
Cosmic Ray production of Beryllium and Boron at high redshift
Recently, new observations of Li6 in Pop II stars of the galactic halo have
shown a surprisingly high abundance of this isotope, about a thousand times
higher than its predicted primordial value. In previous papers, a cosmological
model for the cosmic ray-induced production of this isotope in the IGM has been
developed to explain the observed abundance at low metallicity. In this paper,
given this constraint on the Li6, we calculate the non-thermal evolution with
redshift of D, Be, and B in the IGM. In addition to cosmological cosmic ray
interactions in the IGM, we include additional processes driven by SN
explosions: neutrino spallation and a low energy component in the structures
ejected by outflows to the IGM. We take into account CNO CRs impinging on the
intergalactic gas. Although subdominant in the galactic disk, this process is
shown to produce the bulk of Be and B in the IGM, due to the differential metal
enrichment between structures (where CRs originate) and the IGM. We also
consider the resulting extragalactic gamma-ray background which we find to be
well below existing data. The computation is performed in the framework of
hierarchical structure formation considering several star formation histories
including Pop III stars. We find that D production is negligible and that a
potentially detectable Be and B plateau is produced by these processes at the
time of the formation of the Galaxy (z ~ 3).Comment: 9 pages, 7 figure
L'homme et les mammifères de France métropolitaine : évolution historique et introductions d'espèces dans les milieux humides et aquatiques
De par ses activités diversifiées, l'homme a modifié en permanence la faune mammalienne de France métropolitaine. Responsable de certaines extinctions, il est également à l'origine de réintroductions d'espèces autochtones et d'introductions d'espèces allochtones. On note que 7 des 18 mammifères fréquentant, à des degrés divers, les milieux humides et aquatiques correspondent à des espèces introduites, la plupart du temps à partir d'échappées de captivité. En effet, la finalité principale de l'apport de ces nouvelles espèces a été, à l'origine, l'élevage pour la fourrure, même si la chasse et l'agrément ont joué un rôle non négligeable. L'introduction active des mammifères exotiques sur le territoire métropolitain a débuté à la fin du XIXème siècle et s'est poursuivie jusque dans les années 1960. Par la suite, quelques cas d'introductions, accidentelles pour l'essentiel, ont encore été enregistrés. La communauté scientifique et naturaliste a insisté depuis longtemps sur les conséquences souvent néfastes de ces apports exogènes. De fait, la réglementation s'est renforcée récemment, pour tenter d'empêcher toute nouvelle initiative incontrôlée. À l'inverse, les actions de réintroductions sont soutenues et considérées comme des outils de gestion et de conservation du patrimoine naturel
On the existence of effective potentials in time-dependent density functional theory
We investigate the existence and properties of effective potentials in
time-dependent density functional theory. We outline conditions for a general
solution of the corresponding Sturm-Liouville boundary value problems. We
define the set of potentials and v-representable densities, give a proof of
existence of the effective potentials under certain restrictions, and show the
set of v-representable densities to be independent of the interaction.Comment: 13 page
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