850 research outputs found
Temporal distortion of annual modulation at low recoil energies
We show that the main features of the annual modulation of the signal
expected in a WIMP direct detection experiment, i.e. its sinusoidal dependence
with time, the occurrence of its maxima and minima during the year and (under
some circumstances) even the one-year period, may be affected by relaxing the
isothermal sphere hypothesis in the description of the WIMP velocity phase
space. The most relevant effect is a distortion of the time-behaviour at low
recoil energies for anisotropic galactic halos. While some of these effects
turn out to be relevant at recoil energies below the current detector
thresholds, some others could already be measurable, although some degree of
tuning between the WIMP mass and the experimental parameters would be required.
Either the observation or non-observation of these effects could provide clues
on the phase space distribution of our galactic halo.Comment: 4 pages, 4 figures, typeset with ReVTeX4. The paper may also be found
at http://www.to.infn.it/~fornengo/papers/distortion.ps.g
Do current WIMP direct measurements constrain light relic neutralinos?
New upper bounds on direct detection rates have recently been presented by a
number of experimental collaborations working on searches for WIMPs. In this
paper we analyze how the constraints on relic neutralinos which can be derived
from these results is affected by the uncertainties in the distribution
function of WIMPs in the halo. Various different categories of velocity
distribution functions are considered, and the ensuing implications for
supersymmetric configurations derived. We conservatively conclude that current
experimental data do not constrain neutralinos of small mass (below 50 GeV).Comment: 9 pages, 7 figures, typeset with ReVTeX4. The paper may also be found
at http://www.to.infn.it/~fornengo/papers/constraints05.ps.gz or through
http://www.astroparticle.to.infn.it/index.htm
Mechanisms of the Vertical Secular Heating of a Stellar Disk
We investigate the nonlinear growth stages of bending instability in stellar
disks with exponential radial density profiles.We found that the unstable modes
are global (the wavelengths are larger than the disk scale lengths) and that
the instability saturation level is much higher than that following from a
linear criterion. The instability saturation time scales are of the order of
one billion years or more. For this reason, the bending instability can play an
important role in the secular heating of a stellar disk in the direction.
In an extensive series of numerical -body simulations with a high spatial
resolution, we were able to scan in detail the space of key parameters (the
initial disk thickness , the Toomre parameter , and the ratio of dark
halo mass to disk mass ). We revealed three distinct
mechanisms of disk heating in the direction: bending instability of the
entire disk, bending instability of the bar, and heating on vertical
inhomogeneities in the distribution of stellar matter.Comment: 22 pages including 8 figures. To be published in Astronomy Letters
(v.29, 2003
Theoretical Directional and Modulated Rates for Direct SUSY Dark Matter Detection
Exotic dark matter together with the vacuum energy (cosmological constant)
seem to dominate in the flat Universe. Thus direct dark matter detection is
central to particle physics and cosmology. Supersymmetry provides a natural
dark matter candidate, the lightest supersymmetric particle (LSP). Furthermore
from the knowledge of the density and velocity distribution of the LSP, the
quark substructure of the nucleon and the nuclear structure (form factor and/or
spin response function), one is able to evaluate the event rate for LSP-nucleus
elastic scattering. The thus obtained event rates are, however, very low. So it
is imperative to exploit the two signatures of the reaction, namely the
modulation effect, i.e. the dependence of the event rate on the Earth's motion,
and the directional asymmetry, i.e. the dependence of the rate on the the
relative angle between the direction of the recoiling nucleus and the sun's
velocity. These two signatures are studied in this paper employing various
velocity distributions and a supersymmetric model with universal boundary
conditions at large tan(beta).Comment: 11 LATEX pages, 1 table and 4 ps figures included. Paper presented in
DARK2002, Fourth Heidelberg International Conference on Dark Matter in Astro-
and Particle Physics, Cape Town, South Africa, 4-9 February, 2002, to appear
in the proceedings (to be published by Springer Verlag
Dark matter and Colliders searches in the MSSM
We study the complementarity between dark matter experiments (direct
detection and indirect detections) and accelerator facilities (the CERN LHC and
a TeV Linear Collider) in the framework of the
constrained Minimal Supersymmetric Standard Model (MSSM). We show how
non--universality in the scalar and gaugino sectors can affect the experimental
prospects to discover the supersymmetric particles. The future experiments will
cover a large part of the parameter space of the MSSM favored by WMAP
constraint on the relic density, but there still exist some regions beyond
reach for some extreme (fine tuned) values of the supersymmetric parameters.
Whereas the Focus Point region characterized by heavy scalars will be easily
probed by experiments searching for dark matter, the regions with heavy
gauginos and light sfermions will be accessible more easily by collider
experiments. More informations on both supersymmetry and astrophysics
parameters can be thus obtained by correlating the different signals.Comment: 25 pages, 10 figures, corrected typos and reference adde
Shading by Napier Grass Reduces Malaria Vector Larvae in Natural Habitats in Western Kenya Highlands
Increased human population in the Western Kenya highlands has led to reclamation of natural swamps resulting in the creation of habitats suitable for the breeding of Anopheles gambiae, the major malaria vector in the region. Here we report on a study to restore the reclaimed swamp and reverse its suitability as a habitat for malaria vectors. Napier grass-shaded and non-shaded water channels in reclaimed sites in Western Kenya highlands were studied for the presence and density of mosquito larvae, mosquito species composition, and daily variation in water temperature. Shading was associated with 75.5% and 88.4% (P < 0.0001) reduction in anopheline larvae densities and 78.1% and 88% (P < 0.0001) reduction in Anopheles gambiae sensu lato (s.l.) densities in two sites, respectively. Shading was associated with a 5.7°C, 5.0°C, and 4.7°C, and 1.6°C, 3.9°C, and 2.8°C (for maximum, minimum, and average temperatures, respectively) reduction (P < 0.0001) in water temperatures in the two locations, respectively. An. gambiae s.l. was the dominant species, constituting 83.2% and 73.1%, and 44.5% and 42.3%, of anophelines in non-shaded and shaded channels, respectively, in the two sites, respectively. An. gambiae sensu stricto (s.s.) constituted the majority (97.4%) of An. gambiae s.l., while the rest (2.6%) comprised of Anopheles arabiensis. Minimum water temperature decreased with increasing grass height (P = 0.0039 and P = 0.0415 for Lunyerere and Emutete sites, respectively). The results demonstrate how simple environmental strategies can have a strong impact on vector densities
New records and checklist of aquatic and semi-aquatic Heteroptera (Insecta: Hemiptera: Gerromorpha and Nepomorpha) from the Southern region of Mato Grosso do Sul, Brazil
Water vapour in the atmosphere of a transiting extrasolar planet
Water is predicted to be among, if not the most abundant molecular species
after hydrogen in the atmospheres of close-in extrasolar giant planets
(hot-Jupiters) Several attempts have been made to detect water on an exoplanet,
but have failed to find compelling evidence for it or led to claims that should
be taken with caution. Here we report an analysis of recent observations of the
hot-Jupiter HD189733b taken during the transit, where the planet passed in
front of its parent star. We find that absorption by water vapour is the most
likely cause of the wavelength-dependent variations in the effective radius of
the planet at the infrared wavelengths 3.6, 5.8 and 8 microns. The larger
effective radius observed at visible wavelengths may be due to either star
variability or the presence of clouds/hazes. We explain the most recent thermal
infrared observations of the planet during secondary transit behind the star,
reporting a non-detection of water on HD189733b, as being a consequence of the
nearly isothermal vertical profile of the planet.s atmosphere. Our results show
that water is detectable on extrasolar planets using the primary transit
technique and that the infrared should be a better wavelength region than the
visible, for such searches
Effects of Temperature, Salinity and Fish in Structuring the Macroinvertebrate Community in Shallow Lakes: Implications for Effects of Climate Change
Climate warming may lead to changes in the trophic structure and diversity of shallow lakes as a combined effect of increased temperature and salinity and likely increased strength of trophic interactions. We investigated the potential effects of temperature, salinity and fish on the plant-associated macroinvertebrate community by introducing artificial plants in eight comparable shallow brackish lakes located in two climatic regions of contrasting temperature: cold-temperate and Mediterranean. In both regions, lakes covered a salinity gradient from freshwater to oligohaline waters. We undertook day and night-time sampling of macroinvertebrates associated with the artificial plants and fish and free-swimming macroinvertebrate predators within artificial plants and in pelagic areas. Our results showed marked differences in the trophic structure between cold and warm shallow lakes. Plant-associated macroinvertebrates and free-swimming macroinvertebrate predators were more abundant and the communities richer in species in the cold compared to the warm climate, most probably as a result of differences in fish predation pressure. Submerged plants in warm brackish lakes did not seem to counteract the effect of fish predation on macroinvertebrates to the same extent as in temperate freshwater lakes, since small fish were abundant and tended to aggregate within the macrophytes. The richness and abundance of most plant-associated macroinvertebrate taxa decreased with salinity. Despite the lower densities of plant-associated macroinvertebrates in the Mediterranean lakes, periphyton biomass was lower than in cold temperate systems, a fact that was mainly attributed to grazing and disturbance by fish. Our results suggest that, if the current process of warming entails higher chances of shallow lakes becoming warmer and more saline, climatic change may result in a decrease in macroinvertebrate species richness and abundance in shallow lakes
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