2,164 research outputs found
Identification of stable endogenous reference genes for real-time PCR in the human fetal gonad using an external standard technique
Peer reviewedPostprin
Bounds on Expected Black Hole Spins in Inspiraling Binaries
As a first step towards understanding the angular momentum evolution history
of black holes in merging black-hole/neutron-star binaries, we perform
population synthesis calculations to track the distribution of accretion
histories of compact objects in such binaries. We find that there are three
distinct processes which can possibly contribute to the black-hole spin
magnitude: a birth spin for the black hole, imparted at either (i) the collapse
of a massive progenitor star to a black hole or (ii) the accretion-induced
collapse of a neutron star to a black hole; and (iii) an accretion spin-up when
the already formed black hole [via (i) or (ii)] goes through an accretion
episode (through an accretion disk or a common-envelope phase). Our results
show that, with regard to accretion-induced spinup in merging BH-NS binaries
[method (iii) above], only
{\em accretion episodes associated with common-envelope phases and
hypercritical accretion rates} occur in the formation history of merging black
hole/neutron star binaries. Lacking unambiguous experimental information about
BH birth spins [i.e., regarding the results of processes (i) and (ii)], we
choose two fiducial values for the BH birth angular momentum parameter a=J/M^2,
consistent with observations of (i) NS birth spins (a roughly 0) and (ii) X-ray
binaries (a=0.5). Using these two fiducial values and a conservative upper
bound on the specific angular momentum of accreted matter, we discuss the
expected range of black hole spins in the binaries of interest. We conclude
with comments on the significance of these results for ground-based
gravitational-wave searches of inspiral signals from black hole binaries.Comment: Submitted to ApJ. (v1) Uses emulateapj.cls. 5 figures. (v2):
corrected reference list and uses smaller figures (v3): Includes changes in
response to referee comments, including new discussion of XRBs. Figures
merged, so only 3 figures (v4) Minor typo correction, plus updated abstract
posted onlin
Precession during merger 1: Strong polarization changes are observationally accessible features of strong-field gravity during binary black hole merger
The short gravitational wave signal from the merger of compact binaries
encodes a surprising amount of information about the strong-field dynamics of
merger into frequencies accessible to ground-based interferometers. In this
paper we describe a previously-unknown "precession" of the peak emission
direction with time, both before and after the merger, about the total angular
momentum direction. We demonstrate the gravitational wave polarization encodes
the orientation of this direction to the line of sight. We argue the effects of
polarization can be estimated nonparametrically, directly from the
gravitational wave signal as seen along one line of sight, as a slowly-varying
feature on top of a rapidly-varying carrier. After merger, our results can be
interpreted as a coherent excitation of quasinormal modes of different angular
orders, a superposition which naturally "precesses" and modulates the
line-of-sight amplitude. Recent analytic calculations have arrived at a similar
geometric interpretation. We suspect the line-of-sight polarization content
will be a convenient observable with which to define new high-precision tests
of general relativity using gravitational waves. Additionally, as the nonlinear
merger process seeds the initial coherent perturbation, we speculate the
amplitude of this effect provides a new probe of the strong-field dynamics
during merger. To demonstrate the ubiquity of the effects we describe, we
summarize the post-merger evolution of 104 generic precessing binary mergers.
Finally, we provide estimates for the detectable impacts of precession on the
waveforms from high-mass sources. These expressions may identify new precessing
binary parameters whose waveforms are dissimilar from the existing sample.Comment: 11 figures; v2 includes response to referee suggestion
Testing gravitational parity violation with coincident gravitational waves and short gamma-ray bursts
Gravitational parity violation is a possibility motivated by particle
physics, string theory and loop quantum gravity. One effect of it is amplitude
birefringence of gravitational waves, whereby left and right
circularly-polarized waves propagate at the same speed but with different
amplitude evolution. Here we propose a test of this effect through coincident
observations of gravitational waves and short gamma-ray bursts from binary
mergers involving neutron stars. Such gravitational waves are highly left or
right circularly-polarized due to the geometry of the merger. Using
localization information from the gamma-ray burst, ground-based gravitational
wave detectors can measure the distance to the source with reasonable accuracy.
An electromagnetic determination of the redshift from an afterglow or host
galaxy yields an independent measure of this distance. Gravitational parity
violation would manifest itself as a discrepancy between these two distance
measurements. We exemplify such a test by considering one specific effective
theory that leads to such gravitational parity-violation, Chern-Simons gravity.
We show that the advanced LIGO-Virgo network and all-sky gamma-ray telescopes
can be sensitive to the propagating sector of Chern-Simons gravitational parity
violation to a level roughly two orders of magnitude better than current
stationary constraints from the LAGEOS satellites.Comment: 21 pages, 2 figures, submitted to Phys. Rev.
Coating thermal noise for arbitrary shaped beams
Advanced LIGO's sensitivity will be limited by coating noise. Though this
noise depends on beam shape, and though nongaussian beams are being seriously
considered for advanced LIGO, no published analysis exists to compare the
quantitative thermal noise improvement alternate beams offer. In this paper, we
derive and discuss a simple integral which completely characterizes the
dependence of coating thermal noise on shape. The derivation used applies
equally well, with minor modifications, to all other forms of thermal noise in
the low-frequency limit.Comment: 3 pages. Originally performed in August 2004. Submitted to CQG. (v2)
: Corrections from referee and other
The dependence of test-mass thermal noises on beam shape in gravitational-wave interferometers
In second-generation, ground-based interferometric gravitational-wave
detectors such as Advanced LIGO, the dominant noise at frequencies
Hz to Hz is expected to be due to thermal fluctuations in the
mirrors' substrates and coatings which induce random fluctuations in the shape
of the mirror face. The laser-light beam averages over these fluctuations; the
larger the beam and the flatter its light-power distribution, the better the
averaging and the lower the resulting thermal noise. In semi-infinite mirrors,
scaling laws for the influence of beam shape on the four dominant types of
thermal noise (coating Brownian, coating thermoelastic, substrate Brownian, and
substrate thermoelastic) have been suggested by various researchers and derived
with varying degrees of rigour. Because these scaling laws are important tools
for current research on optimizing the beam shape, it is important to firm up
our understanding of them. This paper (1) gives a summary of the prior work and
of gaps in the prior analyses, (2) gives a unified and rigorous derivation of
all four scaling laws, and (3) explores, relying on work by J. Agresti,
deviations from the scaling laws due to finite mirror size.Comment: 25 pages, 10 figures, submitted to Class. Quantum Gra
Systematic challenges for future gravitational wave measurements of precessing binary black holes
The properties of precessing, coalescing binary black holes are presently
inferred through comparison with two approximate models of compact binary
coalescence. In this work we show these two models often disagree substantially
when binaries have modestly large spins () and modest mass ratios
(). We demonstrate these disagreements using standard figures of
merit and the parameters inferred for recent detections of binary black holes.
By comparing to numerical relativity, we confirm these disagreements reflect
systematic errors. We provide concrete examples to demonstrate that these
systematic errors can significantly impact inferences about astrophysically
significant binary parameters. For the immediate future, parameter inference
for binary black holes should be performed with multiple models (including
numerical relativity), and carefully validated by performing inference under
controlled circumstances with similar synthetic events.Comment: 12 pages, 9 figure
The Slowly Formed Guiselin Brush
We study polymer layers formed by irreversible adsorption from a polymer
melt. Our theory describes an experiment which is a ``slow'' version of that
proposed by Guiselin [Europhys. Lett., v. 17 (1992) p. 225] who considered
instantaneously irreversibly adsorbing chains and predicted a universal density
profile of the layer after swelling with solvent to produce the ``Guiselin
brush.'' Here we ask what happens when adsorption is not instantaneous. The
classic example is chemisorption. In this case the brush is formed slowly and
the final structure depends on the experiment's duration, . We find
the swollen layer consists of an inner region of thickness with approximately constant density and an outer region
extending up to height which has the same density decay as for the Guiselin case.Comment: 7 pages, submitted to Europhysics Letter
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