5,398 research outputs found
Indirect Detection of CMSSM Neutralino Dark Matter with Neutrino Telescopes
We review the prospects of detecting supersymmetric dark matter in the
framework of the Constrained Minimal Supersymmetric Standard Model, and compare
indirect with direct detection capabilities.Comment: 6 pages, 4 figures, presented by J. Orloff at the York IDM02 workshop
(http://www.shef.ac.uk/~phys/idm2002
Neutrino Indirect Detection of Neutralino Dark Matter in the CMSSM
We study potential signals of neutralino dark matter indirect detection by
neutrino telescopes in a wide range of CMSSM parameters. We also compare with
direct detection potential signals taking into account in both cases present
and future experiment sensitivities. Only models with neutralino annihilation
into gauge bosons can satisfy cosmological constraints and current neutrino
indirect detection sensitivities. For both direct and indirect detection, only
next generation experiments will be able to really test this kind of models.Comment: 16 pages, 19 figures; v4: a few clarifications and significant
improvement of reference
Global fluctuations and Gumbel statistics
We explain how the statistics of global observables in correlated systems can
be related to extreme value problems and to Gumbel statistics. This
relationship then naturally leads to the emergence of the generalized Gumbel
distribution G_a(x), with a real index a, in the study of global fluctuations.
To illustrate these findings, we introduce an exactly solvable nonequilibrium
model describing an energy flux on a lattice, with local dissipation, in which
the fluctuations of the global energy are precisely described by the
generalized Gumbel distribution.Comment: 4 pages, 3 figures; final version with minor change
The Kovacs effect in model glasses
We discuss the `memory effect' discovered in the 60's by Kovacs in
temperature shift experiments on glassy polymers, where the volume (or energy)
displays a non monotonous time behaviour. This effect is generic and is
observed on a variety of different glassy systems (including granular
materials). The aim of this paper is to discuss whether some microscopic
information can be extracted from a quantitative analysis of the `Kovacs hump'.
We study analytically two families of theoretical models: domain growth and
traps, for which detailed predictions of the shape of the hump can be obtained.
Qualitatively, the Kovacs effect reflects the heterogeneity of the system: its
description requires to deal not only with averages but with a full probability
distribution (of domain sizes or of relaxation times). We end by some
suggestions for a quantitative analysis of experimental results.Comment: 17 pages, 6 figures; revised versio
Effects of surface cooling and of roughness on the heating (including transition) to the windward plane-of-symmetry of the shuttle orbiter
The theoretical heat-transfer distributions are compared with experimental heat-transfer distributions obtained in Tunnel B at AEDC using a 0.0175 scale model of the space shuttle orbiter configuration for which the first 80% of the windward surface was roughened by a simulated tile misalignment. The theoretical solutions indicate that thinning the boundary layer by surface cooling increased the nondimensionalized value of the local heat-transfer coefficient. Tile misalignment did not significantly affect the heat-transfer rate in regions where the boundary layer was either laminar or turbulent
Dynamical Analysis of Nearby ClustErs. Automated astrometry from the ground: precision proper motions over wide field
The kinematic properties of the different classes of objects in a given
association hold important clues about its member's history, and offer a unique
opportunity to test the predictions of the various models of stellar formation
and evolution. DANCe (standing for Dynamical Analysis of Nearby ClustErs) is a
survey program aimed at deriving a comprehensive and homogeneous census of the
stellar and substellar content of a number of nearby (<1kpc) young (<500Myr)
associations. Whenever possible, members will be identified based on their
kinematics properties, ensuring little contamination from background and
foreground sources. Otherwise, the dynamics of previously confirmed members
will be studied using the proper motion measurements. We present here the
method used to derive precise proper motion measurements, using the Pleiades
cluster as a test bench. Combining deep wide field multi-epoch panchromatic
images obtained at various obervatories over up to 14 years, we derive accurate
proper motions for the sources present in the field of the survey. The datasets
cover ~80 square degrees, centered around the Seven Sisters. Using new tools,
we have computed a catalog of 6116907 unique sources, including proper motion
measurements for 3577478 of them. The catalogue covers the magnitude range
between i=12~24mag, achieving a proper motion accuracy <1mas/yr for sources as
faint as i=22.5mag. We estimate that our final accuracy reaches 0.3mas/yr in
the best cases, depending on magnitude, observing history, and the presence of
reference extragalactic sources for the anchoring onto the ICRS.Comment: Accepted for publication in A&
Linear and non linear response in the aging regime of the 1D trap model
We investigate the behaviour of the response function in the one dimensional
trap model using scaling arguments that we confirm by numerical simulations. We
study the average position of the random walk at time tw+t given that a small
bias h is applied at time tw. Several scaling regimes are found, depending on
the relative values of t, tw and h. Comparison with the diffusive motion in the
absence of bias allows us to show that the fluctuation dissipation relation is,
in this case, valid even in the aging regime.Comment: 5 pages, 3 figures, 3 references adde
Orion revisited. II. The foreground population to Orion A
Following the recent discovery of a large population of young stars in front
of the Orion Nebula, we carried out an observational campaign with the DECam
wide-field camera covering ~10~deg^2 centered on NGC 1980 to confirm, probe the
extent of, and characterize this foreground population of pre-main-sequence
stars. We confirm the presence of a large foreground population towards the
Orion A cloud. This population contains several distinct subgroups, including
NGC1980 and NGC1981, and stretches across several degrees in front of the Orion
A cloud. By comparing the location of their sequence in various color-magnitude
diagrams with other clusters, we found a distance and an age of 380pc and
5~10Myr, in good agreement with previous estimates. Our final sample includes
2123 candidate members and is complete from below the hydrogen-burning limit to
about 0.3Msun, where the data start to be limited by saturation. Extrapolating
the mass function to the high masses, we estimate a total number of ~2600
members in the surveyed region. We confirm the presence of a rich, contiguous,
and essentially coeval population of about 2600 foreground stars in front of
the Orion A cloud, loosely clustered around NGC1980, NGC1981, and a new group
in the foreground of the OMC-2/3. For the area of the cloud surveyed, this
result implies that there are more young stars in the foreground population
than young stars inside the cloud. Assuming a normal initial mass function, we
estimate that between one to a few supernovae must have exploded in the
foreground population in the past few million years, close to the surface of
Orion A, which might be responsible, together with stellar winds, for the
structure and star formation activity in these clouds. This long-overlooked
foreground stellar population is of great significance, calling for a revision
of the star formation history in this region of the Galaxy.Comment: Accepted for publication in A&
Comparison between S. T. radar and in situ balloon measurements
A campaign for simultaneous in situ and remote observation of both troposphere and stratosphere took place near Aire-sur-l'Adour (in southeastern France) on May 4, 1984. The aim of this campaign was a better understanding of the physics of radar echoes. The backscattered signal obtained with a stratosphere-troposphere radar both at the vertical and 15 deg. off vertical is compared with the velocity and temperature measurements made in the same region (about 10 km north of the radar site) by balloon-borne ionic anenometers and temperature sensors. In situ measurements clearly indicate that the temperature fluctuations are not always consistent with the standard turbulent theory. Nevertheless, the assumptions generally made (isotropy and turbulent field in k) and the classical formulation so derived for radar reflectivity are able to reproduce the shape of the radar return power profiles in oblique directions. Another significant result is the confirmation of the role played by the atmospheric stratification in the vertical echo power. It is important to develop these simultaneous in situ and remote experiments for a better description of the dynamical and thermal structure of the atmosphere and for a better understanding of the mechanisms governing clear-air radar reflectivity
Cluster membership probabilities from proper motions and multiwavelength photometric catalogues: I. Method and application to the Pleiades cluster
We present a new technique designed to take full advantage of the high
dimensionality (photometric, astrometric, temporal) of the DANCe survey to
derive self-consistent and robust membership probabilities of the Pleiades
cluster. We aim at developing a methodology to infer membership probabilities
to the Pleiades cluster from the DANCe multidimensional astro-photometric data
set in a consistent way throughout the entire derivation. The determination of
the membership probabilities has to be applicable to censored data and must
incorporate the measurement uncertainties into the inference procedure.
We use Bayes' theorem and a curvilinear forward model for the likelihood of
the measurements of cluster members in the colour-magnitude space, to infer
posterior membership probabilities. The distribution of the cluster members
proper motions and the distribution of contaminants in the full
multidimensional astro-photometric space is modelled with a
mixture-of-Gaussians likelihood. We analyse several representation spaces
composed of the proper motions plus a subset of the available magnitudes and
colour indices. We select two prominent representation spaces composed of
variables selected using feature relevance determination techniques based in
Random Forests, and analyse the resulting samples of high probability
candidates. We consistently find lists of high probability (p > 0.9975)
candidates with 1000 sources, 4 to 5 times more than obtained in the
most recent astro-photometric studies of the cluster.
The methodology presented here is ready for application in data sets that
include more dimensions, such as radial and/or rotational velocities, spectral
indices and variability.Comment: 14 pages, 4 figures, accepted by A&
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