4,091 research outputs found
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
Survey of vector-like fermion extensions of the Standard Model and their phenomenological implications
With the renewed interest in vector-like fermion extensions of the Standard
Model, we present here a study of multiple vector-like theories and their
phenomenological implications. Our focus is mostly on minimal flavor conserving
theories that couple the vector-like fermions to the SM gauge fields and mix
only weakly with SM fermions so as to avoid flavor problems. We present
calculations for precision electroweak and vector-like state decays, which are
needed to investigate compatibility with currently known data. We investigate
the impact of vector-like fermions on Higgs boson production and decay,
including loop contributions, in a wide variety of vector-like extensions and
their parameter spaces.Comment: 43 pages, 17 figures; v2: text modified to improve readability,
references added, journal versio
Angle-dependence of quantum oscillations in YBa2Cu3O6.59 shows free spin behaviour of quasiparticles
Measurements of quantum oscillations in the cuprate superconductors afford a
new opportunity to assess the extent to which the electronic properties of
these materials yield to a description rooted in Fermi liquid theory. However,
such an analysis is hampered by the small number of oscillatory periods
observed. Here we employ a genetic algorithm to globally model the field,
angular, and temperature dependence of the quantum oscillations observed in the
resistivity of YBa2Cu3O6.59. This approach successfully fits an entire data set
to a Fermi surface comprised of two small, quasi-2-dimensional cylinders. A key
feature of the data is the first identification of the effect of Zeeman
splitting, which separates spin-up and spin-down contributions, indicating that
the quasiparticles in the cuprates behave as nearly free spins, constraining
the source of the Fermi surface reconstruction to something other than a
conventional spin density wave with moments parallel to the CuO2 planes.Comment: 8 pages, 4 figure
Severe Lumbar Disability Is Associated With Decreased Psoas Cross-Sectional Area in Degenerative Spondylolisthesis
Study Design: Retrospective cohort. Objectives: Alterations in lumbar paraspinal muscle cross-sectional area (CSA) may correlate with lumbar pathology. The purpose of this study was to compare paraspinal CSA in patients with degenerative spondylolisthesis and severe lumbar disability to those with mild or moderate lumbar disability, as determined by the Oswestry Disability Index (ODI). Methods: We retrospectively reviewed the medical records of 101 patients undergoing lumbar fusion for degenerative spondylolisthesis. Patients were divided into ODI score ≤40 (mild/moderate disability, MMD) and ODI score \u3e40 (severe disability, SD) groups. The total CSA of the psoas and paraspinal muscles were measured on preoperative magnetic resonance imaging (MRI). Results: There were 37 patients in the SD group and 64 in the MMD group. Average age and body mass index were similar between groups. For the paraspinal muscles, we were unable to demonstrate any significant differences in total CSA between the groups. Psoas muscle CSA was significantly decreased in the SD group compared with the MMD group (1010.08 vs 1178.6 mm2, P =.041). Multivariate analysis found that psoas CSA in the upper quartile was significantly protective against severe disability (P =.013). Conclusions: We found that patients with severe lumbar disability had no significant differences in posterior lumbar paraspinal CSA when compared with those with mild/moderate disability. However, severely disabled patients had significantly decreased psoas CSA, and larger psoas CSA was strongly protective against severe disability, suggestive of a potential association with psoas atrophy and worsening severity of lumbar pathology. © The Author(s) 2018
A blind search for a common signal in gravitational wave detectors
We propose a blind, template-free method for the extraction of a common
signal between the Hanford and Livingston detectors and apply it especially to
the GW150914 event. We construct a log-likelihood method that maximizes the
cross-correlation between each detector and the common signal and minimizes the
cross-correlation between the residuals. The reliability of this method is
tested using simulations with an injected common signal. Finally, our method is
used to assess the quality of theoretical gravitational wave templates for
GW150914.Comment: Accepted for publication in JCA
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