58 research outputs found
Noise residuals for GW150914 using maximum likelihood and numerical relativity templates
We reexamine the results presented in a recent work by Nielsen et al. [1], in
which the properties of the noise residuals in the 40\,ms chirp domain of
GW150914 were investigated. This paper confirmed the presence of strong (i.e.,
about 0.80) correlations between residual noise in the Hanford and Livingston
detectors in the chirp domain as previously seen by us [2] when using a
numerical relativity template given in [3]. It was also shown in [1] that a
so-called maximum likelihood template can reduce these statistically
significant cross-correlations. Here, we demonstrate that the reduction of
correlation and statistical significance is due to (i) the use of a peculiar
template which is qualitatively different from the properties of GW150914
originally published by LIGO, (ii) a suspicious MCMC chain, (iii) uncertainties
in the matching of the maximum likelihood (ML) template to the data in the
Fourier domain, and (iv) a biased estimation of the significance that gives
counter-intuitive results. We show that rematching the maximum likelihood
template to the data in the 0.2\,s domain containing the GW150914 signal
restores these correlations at the level of of those found in [1]. With
necessary corrections, the probability given in [1] will decrease by more than
one order of magnitude. Since the ML template is itself problematic, results
associated with this template are illustrative rather than final.Comment: Minor correction
On the time lags of the LIGO signals
To date, the LIGO collaboration has detected three gravitational wave (GW)
events appearing in both its Hanford and Livingston detectors. In this article
we reexamine the LIGO data with regard to correlations between the two
detectors. With special focus on GW150914, we report correlations in the
detector noise which, at the time of the event, happen to be maximized for the
same time lag as that found for the event itself. Specifically, we analyze
correlations in the calibration lines in the vicinity of 35\,Hz as well as the
residual noise in the data after subtraction of the best-fit theoretical
templates. The residual noise for the other two events, GW151226 and GW170104,
exhibits similar behavior. A clear distinction between signal and noise
therefore remains to be established in order to determine the contribution of
gravitational waves to the detected signals.Comment: The body of the current version is essentially identical to the
previous one submitted to arxiv and JCAP. In order to meet the various
suggestions of the referees, we have included an extended and detailed
Appendix. This Appendix also contains significant new results that provide
additional support for our conclusions. This version of our manuscript has
been accepted for publication by JCA
Degeneracy of gravitational waveforms in the context of GW150914
We study the degeneracy of theoretical gravitational waveforms for binary
black hole mergers using an aligned-spin effective-one-body model. After
appropriate truncation, bandpassing, and matching, we identify regions in the
mass--spin parameter space containing waveforms similar to the template
proposed for GW150914, with masses and , using the cross-correlation coefficient as a measure of
the similarity between waveforms. Remarkably high cross-correlations are found
across broad regions of parameter space. The associated uncertanties exceed
these from LIGO's Bayesian analysis considerably. We have shown that waveforms
with greatly increased masses, such as and , and strong anti-aligned spins ( and )
yield almost the same signal-to-noise ratio in the strain data for GW150914.Comment: Accepted for publication in JCA
Auto and cross correlation of phases of the whole-sky CMB and foreground maps from the 1-year WMAP data
The issue of non-Gaussianity is not only related to distinguishing the
theories of the origin of primordial fluctuations, but also crucial for the
determination of cosmological parameters in the framework of inflation
paradigm. We present an advenced method for testing non-Gaussianity on the
whole-sky CMB anisotropies. This method is based on the Kuiper's statistic to
probe the two-dimensional uniformity on a periodic mapping square associating
phases: return mapping of phases of the derived CMB (similar to auto
correlation) and cross correlations between phases of the derived CMB and
foregrounds. Since phases reflect morphology, detection of cross correlation of
phases signifies the contamination of foreground signals in the derived CMB
map. The advantage of this method is that one can cross check the auto and
cross correlation of phases of the derived CMB and foregrounds, and mark off
those multipoles in which the non-Gaussianity results from the foreground
contaminations. We apply this statistic on the derived signals from the 1-year
WMAP data. The auto-correlations of phases from the ILC map shows the
significance above 95% CL against the random phase hypothesis on 17 spherical
harmonic multipoles, among which some have pronounced cross correlations with
the foreground maps. We conclude that most of the non-Gaussianity found in the
derived CMB maps are from foreground contaminations, except, among others, l=6.
With this method we are better equipped to approach the issue of
non-Gaussianity of primordial origin for the upcoming PLANCK mission.Comment: 2 figures added: new representation of reconstructed (from 1D Fourier
composition) DT distribution for each multipole number el
Primordial magnetic field and non-Gaussianity of the 1-year Wilkinson Microwave Anisotropy Probe (WMAP) data
Alfven turbulence caused by statistically isotropic and homogeneous
primordial magnetic field induces correlations in the cosmic microwave
background anisotropies. The correlations are specifically between spherical
harmonic modes a_{l-1,m} and a_{l+1,m}. In this paper we approach this issue
from phase analysis of the CMB maps derived from the WMAP data sets. Using
circular statistics and return phase mapping we examine phase correlation of
\Delta l=2 for the primordial non-Gaussianity caused by the Alfven turbulence
at the epoch of recombination. Our analyses show that such specific features
from the power-law Alfven turbulence do not contribute significantly in the
phases of the maps and could not be a source of primordial non-Gaussianity of
the CMB.Comment: 8 pages, 7 figures, ApJ accepted with minor changes and the
explanation on the whitened derived CMB map
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