636 research outputs found
The optimal search for an astrophysical gravitational-wave background
Roughly every 2-10 minutes, a pair of stellar mass black holes merge
somewhere in the Universe. A small fraction of these mergers are detected as
individually resolvable gravitational-wave events by advanced detectors such as
LIGO and Virgo. The rest contribute to a stochastic background. We derive the
statistically optimal search strategy for a background of unresolved binaries.
Our method applies Bayesian parameter estimation to all available data. Using
Monte Carlo simulations, we demonstrate that the search is both "safe" and
effective: it is not fooled by instrumental artefacts such as glitches, and it
recovers simulated stochastic signals without bias. Given realistic
assumptions, we estimate that the search can detect the binary black hole
background with about one day of design sensitivity data versus
months using the traditional cross-correlation search. This framework
independently constrains the merger rate and black hole mass distribution,
breaking a degeneracy present in the cross-correlation approach. The search
provides a unified framework for population studies of compact binaries, which
is cast in terms of hyper-parameter estimation. We discuss a number of
extensions and generalizations including: application to other sources (such as
binary neutron stars and continuous-wave sources), simultaneous estimation of a
continuous Gaussian background, and applications to pulsar timing.Comment: 16 pages, 9 figure
Fast Simulation of Gaussian-Mode Scattering for Precision Interferometry
Understanding how laser light scatters from realistic mirror surfaces is
crucial for the design, com- missioning and operation of precision
interferometers, such as the current and next generation of gravitational-wave
detectors. Numerical simulations are indispensable tools for this task but
their utility can in practice be limited by the computational cost of
describing the scattering process. In this paper we present an efficient method
to significantly reduce the computational cost of optical simulations that
incorporate scattering. This is accomplished by constructing a near optimal
representation of the complex, multi-parameter 2D overlap integrals that
describe the scattering process (referred to as a reduced order quadrature). We
demonstrate our technique by simulating a near-unstable Fabry-Perot cavity and
its control signals using similar optics to those installed in one of the LIGO
gravitational-wave detectors. We show that using reduced order quadrature
reduces the computational time of the numerical simulation from days to minutes
(a speed-up of ) whilst incurring negligible errors. This
significantly increases the feasibility of modelling interferometers with
realistic imperfections to overcome current limits in state-of-the-art optical
systems. Whilst we focus on the Hermite-Gaussian basis for describing the
scattering of the optical fields, our method is generic and could be applied
with any suitable basis. An implementation of this reduced order quadrature
method is provided in the open source interferometer simulation software
Finesse.Comment: 15 pages, 11 figure
Parallelized Inference for Gravitational-Wave Astronomy
Bayesian inference is the workhorse of gravitational-wave astronomy, for
example, determining the mass and spins of merging black holes, revealing the
neutron star equation of state, and unveiling the population properties of
compact binaries. The science enabled by these inferences comes with a
computational cost that can limit the questions we are able to answer. This
cost is expected to grow. As detectors improve, the detection rate will go up,
allowing less time to analyze each event. Improvement in low-frequency
sensitivity will yield longer signals, increasing the number of computations
per event. The growing number of entries in the transient catalog will drive up
the cost of population studies. While Bayesian inference calculations are not
entirely parallelizable, key components are embarrassingly parallel:
calculating the gravitational waveform and evaluating the likelihood function.
Graphical processor units (GPUs) are adept at such parallel calculations. We
report on progress porting gravitational-wave inference calculations to GPUs.
Using a single code - which takes advantage of GPU architecture if it is
available - we compare computation times using modern GPUs (NVIDIA P100) and
CPUs (Intel Gold 6140). We demonstrate speed-ups of for
compact binary coalescence gravitational waveform generation and likelihood
evaluation and more than for population inference within the
lifetime of current detectors. Further improvement is likely with continued
development. Our python-based code is publicly available and can be used
without familiarity with the parallel computing platform, CUDA.Comment: 5 pages, 4 figures, submitted to PRD, code can be found at
https://github.com/ColmTalbot/gwpopulation
https://github.com/ColmTalbot/GPUCBC
https://github.com/ADACS-Australia/ADACS-SS18A-RSmith Add demonstration of
improvement in BNS spi
Measuring eccentricity in binary black hole inspirals with gravitational waves
When binary black holes form in the field, it is expected that their orbits
typically circularize before coalescence. In galactic nuclei and globular
clusters, binary black holes can form dynamically. Recent results suggest that
of mergers in globular clusters result from three-body
interactions. These three-body interactions are expected to induce significant
orbital eccentricity when they enter the Advanced LIGO band at a
gravitational-wave frequency of 10 Hz. Measurements of binary black hole
eccentricity therefore provide a means for determining whether or not dynamic
formation is the primary channel for producing binary black hole mergers. We
present a framework for performing Bayesian parameter estimation on
gravitational-wave observations of black hole inspirals. Using this framework,
and employing the non-spinning, inspiral-only EccentricFD waveform approximant,
we determine the minimum detectable eccentricity for an event with masses and
distance similar to GW150914. At design sensitivity, we find that the current
generation of advanced observatories will be sensitive to orbital
eccentricities of at a gravitational-wave frequency of 10 Hz,
demonstrating that existing detectors can use eccentricity to distinguish
between circular field binaries and globular cluster triples. We compare this
result to eccentricity distributions predicted to result from three black hole
binary formation channels, showing that measurements of eccentricity could be
used to infer the population properties of binary black holes.Comment: 12 pages, 7 figures, 2 table
An analysis and visualization of the output mode-matching requirements for squeezing in Advanced LIGO and future gravitational wave detectors
The sensitivity of ground-based gravitational wave (GW) detectors will be
improved in the future via the injection of frequency-dependent squeezed
vacuum. The achievable improvement is ultimately limited by losses of the
interferometer electromagnetic field that carries the GW signal. The analysis
and reduction of optical loss in the GW signal chain will be critical for
optimal squeezed light-enhanced interferometry. In this work we analyze a
strategy for reducing output-side losses due to spatial mode mismatch between
optical cavities with the use of adaptive optics. Our goal is not to design a
detector from the top down, but rather to minimize losses within the current
design. Accordingly, we consider actuation on optics already present and one
transmissive optic to be added between the signal recycling mirror and the
output mode cleaner. The results of our calculation show that adaptive
mode-matching with the current Advanced LIGO design is a suitable strategy for
loss reduction that provides less than 2% mean output mode-matching loss. The
range of actuation required is +47 uD on SR3, +140 mD on OM1 and OM2, +50 mD on
the SRM substrate, and -50 mD on the added new transmissive optic. These
requirements are within the demonstrated ranges of real actuators in similar or
identical configurations to the proposed implementation. We also present a
novel technique that graphically illustrates the matching of interferometer
modes and allows for a quantitative comparison of different combinations of
actuators.Comment: Matches version accepted in PR
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