398 research outputs found
Recherche de coalescences binaires - Etalonnage du détecteur d'ondes gravitationnelles VIRGO
Ce compte-rendu présente la préparation en cours de l'analyse des données du détecteur d'ondes gravitationnelles VIRGO pour la recherche de coalescences binaires, et plus particulièrement de l'étalonnage du détecteur pour la reconstruction des données et de la recherche de signal
Remarks on endomorphisms and rational points
Let X be a variety over a number field and let f: X --> X be an "interesting"
rational self-map with a fixed point q. We make some general remarks concerning
the possibility of using the behaviour of f near q to produce many rational
points on X. As an application, we give a simplified proof of the potential
density of rational points on the variety of lines of a cubic fourfold
(originally obtained by Claire Voisin and the first author in 2007).Comment: LaTeX, 22 pages. v2: some minor observations added, misprints
corrected, appendix modified
Holomorphic symplectic geometry: a problem list
A list of open problems on holomorphic symplectic, contact and Poisson
manifolds
Template-based searches for gravitational waves: efficient lattice covering of flat parameter spaces
The construction of optimal template banks for matched-filtering searches is
an example of the sphere covering problem. For parameter spaces with
constant-coefficient metrics a (near-) optimal template bank is achieved by the
A_n* lattice, which is the best lattice-covering in dimensions n <= 5, and is
close to the best covering known for dimensions n <= 16. Generally this
provides a substantially more efficient covering than the simpler hyper-cubic
lattice. We present an algorithm for generating lattice template banks for
constant-coefficient metrics and we illustrate its implementation by generating
A_n* template banks in n=2,3,4 dimensions.Comment: 10 pages, submitted to CQG for proceedings of GWDAW1
Upper Limits from Counting Experiments with Multiple Pipelines
In counting experiments, one can set an upper limit on the rate of a Poisson
process based on a count of the number of events observed due to the process.
In some experiments, one makes several counts of the number of events, using
different instruments, different event detection algorithms, or observations
over multiple time intervals. We demonstrate how to generalize the classical
frequentist upper limit calculation to the case where multiple counts of events
are made over one or more time intervals using several (not necessarily
independent) procedures. We show how different choices of the rank ordering of
possible outcomes in the space of counts correspond to applying different
levels of significance to the various measurements. We propose an ordering that
is matched to the sensitivity of the different measurement procedures and show
that in typical cases it gives stronger upper limits than other choices. As an
example, we show how this method can be applied to searches for
gravitational-wave bursts, where multiple burst-detection algorithms analyse
the same data set, and demonstrate how a single combined upper limit can be set
on the gravitational-wave burst rate.Comment: 26 pages (CQG style), 8 figures. Added study of robustness of limits
Multi-Hamiltonian structures for r-matrix systems
For the rational, elliptic and trigonometric r-matrices, we exhibit the links
between three "levels" of Poisson spaces: (a) Some finite-dimensional spaces of
matrix-valued holomorphic functions on the complex line; (b) Spaces of spectral
curves and sheaves supported on them; (c) Symmetric products of a surface. We
have, at each level, a linear space of compatible Poisson structures, and the
maps relating the levels are Poisson. This leads in a natural way to Nijenhuis
coordinates for these spaces. At level (b), there are Hamiltonian systems on
these spaces which are integrable for each Poisson structure in the family, and
which are such that the Lagrangian leaves are the intersections of the
symplective leaves over the Poisson structures in the family. Specific examples
include many of the well-known integrable systems.Comment: 26 pages, Plain Te
Benefits of joint LIGO -- Virgo coincidence searches for burst and inspiral signals
We examine the benefits of performing a joint LIGO--Virgo search for
transient signals. We do this by adding burst and inspiral signals to 24 hours
of simulated detector data. We find significant advantages to performing a
joint coincidence analysis, above either a LIGO only or Virgo only search.
These include an increased detection efficiency, at a fixed false alarm rate,
to both burst and inspiral events and an ability to reconstruct the sky
location of a signal.Comment: 11 pages 8 figures, Amaldi 6 proceeding
Contact Moishezon threefolds with second Betti number one
We prove that the only contact Moishezon threefold having second Betti number
equal to one is the projective space.Comment: 5 pages. v2: exposition improved as suggested by the referee. To
appear in Archiv der Mat
A comparison of methods for gravitational wave burst searches from LIGO and Virgo
The search procedure for burst gravitational waves has been studied using 24
hours of simulated data in a network of three interferometers (Hanford 4-km,
Livingston 4-km and Virgo 3-km are the example interferometers). Several
methods to detect burst events developed in the LIGO Scientific Collaboration
(LSC) and Virgo collaboration have been studied and compared. We have performed
coincidence analysis of the triggers obtained in the different interferometers
with and without simulated signals added to the data. The benefits of having
multiple interferometers of similar sensitivity are demonstrated by comparing
the detection performance of the joint coincidence analysis with LSC and Virgo
only burst searches. Adding Virgo to the LIGO detector network can increase by
50% the detection efficiency for this search. Another advantage of a joint
LIGO-Virgo network is the ability to reconstruct the source sky position. The
reconstruction accuracy depends on the timing measurement accuracy of the
events in each interferometer, and is displayed in this paper with a fixed
source position example.Comment: LIGO-Virgo working group submitted to PR
A template bank to search for gravitational waves from inspiralling compact binaries: II. Phenomenological model
Matched filtering is used to search for gravitational waves emitted by
inspiralling compact binaries in data from ground-based interferometers. One of
the key aspects of the detection process is the deployment of a set of
templates, also called a template bank, to cover the astrophysically
interesting region of the parameter space. In a companion paper, we described
the template-bank algorithm used in the analysis of LIGO data to search for
signals from non-spinning binaries made of neutron star and/or stellar-mass
black holes; this template bank is based upon physical template families. In
this paper, we describe the phenomenological template bank that was used to
search for gravitational waves from non-spinning black hole binaries (from
stellar mass formation) in the second, third and fourth LIGO science runs. We
briefly explain the design of the bank, whose templates are based on a
phenomenological detection template family. We show that this template bank
gives matches greater than 95% with the physical template families that are
expected to be captured by the phenomenological templates.Comment: 10 pages, 9 figure
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