15,824 research outputs found
Searches for Gravitational Waves from Binary Neutron Stars: A Review
A new generation of observatories is looking for gravitational waves. These
waves, emitted by highly relativistic systems, will open a new window for ob-
servation of the cosmos when they are detected. Among the most promising
sources of gravitational waves for these observatories are compact binaries in
the final min- utes before coalescence. In this article, we review in brief
interferometric searches for gravitational waves emitted by neutron star
binaries, including the theory, instru- mentation and methods. No detections
have been made to date. However, the best direct observational limits on
coalescence rates have been set, and instrumentation and analysis methods
continue to be refined toward the ultimate goal of defining the new field of
gravitational wave astronomy.Comment: 30 pages, 5 Figures, to appear in "Short-Period Binary Stars:
Observations, Analyses, and Results", Ed.s Eugene F. Milone, Denis A. Leahy,
David W. Hobil
The path to the enhanced and advanced LIGO gravitational-wave detectors
We report on the status of the Laser Interferometric Gravitational-Wave
Observatory (LIGO) and the plans and progress towards Enhanced and Advanced
LIGO. The initial LIGO detectors have finished a two year long data run during
which a full year of triple-coincidence data was collected at design
sensitivity. Much of this run was also coincident with the data runs of
interferometers in Europe, GEO600 and Virgo. The joint analysis of data from
this international network of detectors is ongoing. No gravitational wave
signals have been detected in analyses completed to date. Currently two of the
LIGO detectors are being upgraded to increase their sensitivity in a program
called Enhanced LIGO. The Enhanced LIGO detectors will start another roughly
one year long data run with increased sensitivity in 2009. In parallel,
construction of Advanced LIGO, a major upgrade to LIGO, has begun. Installation
and commissioning of Advanced LIGO hardware at the LIGO sites will commence at
the end of the Enhanced LIGO data run in 2011. When fully commissioned, the
Advanced LIGO detectors will be ten times as sensitive as the initial LIGO
detectors. Advanced LIGO is expected to make several gravitational wave
detections per year.Comment: 11 pages, 5 figure
Analysis of millimetre-wave polarization diverse multiple-input multiple-output capacity
Millimetre-waves offer the possibility of wide bandwidth and consequently high data rate for wireless communications. For both uni- and dual-polarized systems, signals sent over a link may suffer severe degradation due to antenna misalignment. Orientation robustness may be enhanced by the use of mutual orthogonality in three dimensions. Multiple-input multiple-output polarization diversity offers a way of improving signal reception without the limitations associated with spatial diversity. Scattering effects often assist propagation through multipath. However, high path loss at millimetre-wave frequencies may limit any reception enhancement through scattering. We show that the inclusion of a third orthogonal dipole provides orientation robustness in this setting, as well as in a rich scattering environment, by means of a Rician fading channel model covering all orientations for a millimetre-wave, tri-orthogonal, half-wave dipole transmitter and receiver employing polarization diversity. Our simulation extends the analysis into three dimensions, fully exploiting individual sub-channel paths. In both the presence and absence of multipath effects, capacity is observed to be higher than that of a dual-polarized system over the majority of a field of view.Nicholas P. Lawrence, Brian W.-H.Ng, Hedley J. Hansen, and Derek Abbot
Methods for Reducing False Alarms in Searches for Compact Binary Coalescences in LIGO Data
The LIGO detectors are sensitive to a variety of noise transients of
non-astrophysical origin. Instrumental glitches and environmental disturbances
increase the false alarm rate in the searches for gravitational waves. Using
times already identified when the interferometers produced data of questionable
quality, or when the channels that monitor the interferometer indicated
non-stationarity, we have developed techniques to safely and effectively veto
false triggers from the compact binary coalescences (CBCs) search pipeline
Renormalizing Heavy Quark Effective Theory at O(1/m_Q^3)
We present a calculation of the renormalized HQET Lagrangian at order
O(1/m_Q^3) in the one particle sector. The anomalous dimensions of local
operators and time ordered products of dimension 7 contributing at this order
are calculated in the one loop approximation. We show that a careful treatment
of the time ordered products is necessary to arrive at a gauge independent
renormalized lagrangian. Our result sets the stage for an investigation of
reparametrization invariance at O(1/m_Q^3).Comment: Latex, epsfig. Improved teXnology and modified conclusions. The
complete paper, including figures, is also available via anonymous ftp at
ftp://ttpux2.physik.uni-karlsruhe.de/ , or via www at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints
Progress towards Gravitational Wave Astronomy
I will review the most recent and interesting results from gravitational wave
detection experiments, concentrating on recent results from the LIGO Scientific
Collaboration (LSC). I will outline the methodologies utilized in the searches,
explain what can be said in the case of a null result, what quantities may be
constrained. I will compare these results with prior expectations and discuss
their significance. As I go along I will outline the prospects for future
improvements.Comment: Based on a talk presented at the joint "18th International Conference
on General Relativity and Gravitation" and "7th Amaldi Conference on
Gravitational Waves", 8-13 July 2007, Sydney, Australi
Search for Gravitational Wave Ringdowns from Perturbed Intermediate Mass Black Holes in LIGO-Virgo Data from 2005-2010
We report results from a search for gravitational waves produced by perturbed intermediate mass black holes (IMBH) in data collected by LIGO and Virgo between 2005 and 2010. The search was sensitive to astrophysical sources that produced damped sinusoid gravitational wave signals, also known as ringdowns, with frequency 50 less than or equal to italic f0/Hz less than or equal to 2000 and decay timescale 0.0001 approximately less than t/s approximately less than 0.1 characteristic of those produced in mergers of IMBH pairs. No significant gravitational wave candidate was detected. We report upper limits on the astrophysical coalescence rates of IMBHs with total binary mass 50 less than or equal to M/solar mass less than or equal to 450 and component mass ratios of either 1:1 or 4:1. For systems with total mass 100 less than or equal to M/solar mass 150, we report a 90%-confidence upper limit on the rate of binary IMBH mergers with non-spinning and equal mass components of 6:9 x 10(exp 8) Mpc(exp -3)yr(exp -1). We also report a rate upper limit for ringdown waveforms from perturbed IMBHs, radiating 1% of their mass as gravitational waves in the fundamental, l=m=2, oscillation mode, that is nearly three orders of magnitude more stringent than previous results
Electron-deuteron scattering in the equal-time formalism: beyond the impulse approximation
Using a three-dimensional formalism that includes relativistic kinematics,
the effects of negative-energy states, approximate boosts of the two-body
system, and current conservation, we calculate the electromagnetic form factors
of the deuteron up to Q^2 of 4 GeV^2. This is done using a dynamical boost for
two-body systems with spin. We first compute form factors in impulse
approxmation, but then also add an isoscalar meson-exchange current of pion
range that involves the gamma-pi contact operator associated with pseudovector
pi-N coupling. We also consider effects of the rho-pi-gamma meson-exchange
current. The experimentally measured quantities A, B, and t20 are calculated
over the kinematic range probed in recent Jefferson Laboratory experiments. The
rho-pi-gamma meson-exchange current provides significant strength in A at large
Q^2 and the gamma-pi contact-term exchange current shifts t20, providing good
agreement with the JLab data. Relativistic effects and the gamma-pi
meson-exchange current do not provide an explanation of the B observable, but
the rho-pi-gamma current could help to provide agreement if a nonstandard value
is used for the tensor rho-N coupling that enters this contribution.Comment: 15 pages, 10 figures. (v2) Added references on rho-pi-gamma current
as well as comparison to recent Novosibirsk data on T20. Implemented
\includegraphics in place of \BoxedEPSF. (v3) Modified in order to clarify
the nature of the boost we implemented for particles with spin. Other minor
changes. Version to be published in Physical Review
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