28 research outputs found
Bayesian Limits on Primordial Isotropy Breaking
It is often assumed that primordial perturbations are statistically
isotropic, which implies, among other properties, that their power spectrum is
invariant under rotations. In this article, we test this assumption by placing
model-independent bounds on deviations from rotational invariance of the
primordial spectrum. Using five-year WMAP cosmic microwave anisotropy maps, we
set limits on the overall norm and the amplitude of individual components of
the primordial spectrum quadrupole. We find that there is no significant
evidence for primordial isotropy breaking, and that an eventually non-vanishing
quadrupole has to be subdominant.Comment: 6 double-column pages, 2 figues and 2 tables. Uses REVTeX
Characterization of Enhanced Interferometric Gravitational Wave Detectors and Studies of Numeric Simulations for Compact-Binary Coalescences
Gravitational waves are a consequence of the general theory of relativity. Direct detection of such waves will provide a wealth of information about physics, astronomy, and cosmology. A worldwide effort is currently underway to make the first direct detection of gravitational waves. The global network of detectors includes the Laser Interferometer Gravitational-wave Observatory (LIGO), which recently completed its sixth science run.
A particularly promising source of gravitational waves is a binary system consisting of two neutron stars and/or black holes. As the objects orbit each other they emit gravitational radiation, lose energy, and spiral inwards. This produces a characteristic ``chirp\u27\u27 signal for which we can search in the LIGO data. Currently this is done using matched-filter techniques, which correlate the detector data against analytic models of the emitted gravitational waves. Several choices must be made in constructing a search for signals from such binary coalescences.
Any discrepancy between the signals and the models used will reduce the effectiveness of the matched filter. However, the analytic models are based on approximations which are not valid through the entire evolution of the binary. In recent years numerical relativity has had impressive success in simulating the final phases of the coalescence of binary black holes. While numerical relativity is too computationally expensive to use directly in the search, this progress has made it possible to perform realistic tests of the LIGO searches. The results of such tests can be used to improve the efficiency of searches.
Conversely, noise in the LIGO and Virgo detectors can reduce the efficiency. This must be addressed by characterizing the quality of the data from the detectors, and removing from the analysis times that will be detrimental to the search.
In this thesis we utilize recent results from numerical relativity to study both the degree to which analytic models match realistic waveforms and the ability of LIGO searches to make detections. We also apply the matched-filter search to the problem of removing times of excess noise from the search
The PyCBC search for gravitational waves from compact binary coalescence
We describe the PyCBC search for gravitational waves from compact-object
binary coalescences in advanced gravitational-wave detector data. The search
was used in the first Advanced LIGO observing run and unambiguously identified
two black hole binary mergers, GW150914 and GW151226. At its core, the PyCBC
search performs a matched-filter search for binary merger signals using a bank
of gravitational-wave template waveforms. We provide a complete description of
the search pipeline including the steps used to mitigate the effects of noise
transients in the data, identify candidate events and measure their statistical
significance. The analysis is able to measure false-alarm rates as low as one
per million years, required for confident detection of signals. Using data from
initial LIGO's sixth science run, we show that the new analysis reduces the
background noise in the search, giving a 30% increase in sensitive volume for
binary neutron star systems over previous searches.Comment: 29 pages, 7 figures, accepted by Classical and Quantum Gravit
Comparison of high-accuracy numerical simulations of black-hole binaries with stationary phase post-Newtonian template waveforms for Initial and Advanced LIGO
We study the effectiveness of stationary-phase approximated post-Newtonian
waveforms currently used by ground-based gravitational-wave detectors to search
for the coalescence of binary black holes by comparing them to an accurate
waveform obtained from numerical simulation of an equal-mass non-spinning
binary black hole inspiral, merger and ringdown. We perform this study for the
Initial- and Advanced-LIGO detectors. We find that overlaps between the
templates and signal can be improved by integrating the match filter to higher
frequencies than used currently. We propose simple analytic frequency cutoffs
for both Initial and Advanced LIGO, which achieve nearly optimal matches, and
can easily be extended to unequal-mass, spinning systems. We also find that
templates that include terms in the phase evolution up to 3.5 pN order are
nearly always better, and rarely significantly worse, than 2.0 pN templates
currently in use. For Initial LIGO we recommend a strategy using templates that
include a recently introduced pseudo-4.0 pN term in the low-mass (M \leq 35
\MSun) region, and 3.5 pN templates allowing unphysical values of the
symmetric reduced mass above this. This strategy always achieves
overlaps within 0.3% of the optimum, for the data used here. For Advanced LIGO
we recommend a strategy using 3.5 pN templates up to M=12 \MSun, 2.0 pN
templates up to M=21 \MSun, pseudo-4.0 pN templates up to 65 \MSun, and 3.5
pN templates with unphysical for higher masses. This strategy always
achieves overlaps within 0.7% of the optimum for Advanced LIGO.Comment: 20 pages, 11 figures. Presented at NRDA 200
Testing gravitational-wave searches with numerical relativity waveforms: Results from the first Numerical INJection Analysis (NINJA) project
The Numerical INJection Analysis (NINJA) project is a collaborative effort
between members of the numerical relativity and gravitational-wave data
analysis communities. The purpose of NINJA is to study the sensitivity of
existing gravitational-wave search algorithms using numerically generated
waveforms and to foster closer collaboration between the numerical relativity
and data analysis communities. We describe the results of the first NINJA
analysis which focused on gravitational waveforms from binary black hole
coalescence. Ten numerical relativity groups contributed numerical data which
were used to generate a set of gravitational-wave signals. These signals were
injected into a simulated data set, designed to mimic the response of the
Initial LIGO and Virgo gravitational-wave detectors. Nine groups analysed this
data using search and parameter-estimation pipelines. Matched filter
algorithms, un-modelled-burst searches and Bayesian parameter-estimation and
model-selection algorithms were applied to the data. We report the efficiency
of these search methods in detecting the numerical waveforms and measuring
their parameters. We describe preliminary comparisons between the different
search methods and suggest improvements for future NINJA analyses.Comment: 56 pages, 25 figures; various clarifications; accepted to CQ