1,084 research outputs found
High Sensitivity Torsion Balance Tests for LISA Proof Mass Modeling
We have built a highly sensitive torsion balance to investigate small forces
between closely spaced gold coated surfaces. Such forces will occur between the
LISA proof mass and its housing. These forces are not well understood and
experimental investigations are imperative. We describe our torsion balance and
present the noise of the system. A significant contribution to the LISA noise
budget at low frequencies is the fluctuation in the surface potential
difference between the proof mass and its housing. We present first results of
these measurements with our apparatus.Comment: 6th International LISA Symposiu
Test of the Equivalence Principle Using a Rotating Torsion Balance
We used a continuously rotating torsion balance instrument to measure the
acceleration difference of beryllium and titanium test bodies towards sources
at a variety of distances. Our result Delta a=(0.6+/-3.1)x10^-15 m/s^2 improves
limits on equivalence-principle violations with ranges from 1 m to infinity by
an order of magnitude. The Eoetvoes parameter is eta=(0.3+/-1.8)x10^-13. By
analyzing our data for accelerations towards the center of the Milky Way we
find equal attractions of Be and Ti towards galactic dark matter, yielding
eta=(-4 +/- 7)x10^-5. Space-fixed differential accelerations in any direction
are limited to less than 8.8x10^-15 m/s^2 with 95% confidence.Comment: 4 pages, 4 figures; accepted for publication in PR
Late Time Tail of Wave Propagation on Curved Spacetime
The late time behavior of waves propagating on a general curved spacetime is
studied. The late time tail is not necessarily an inverse power of time. Our
work extends, places in context, and provides understanding for the known
results for the Schwarzschild spacetime. Analytic and numerical results are in
excellent agreement.Comment: 11 pages, WUGRAV-94-1
Evolution equations for slowly rotating stars
We present a hyperbolic formulation of the evolution equations describing
non-radial perturbations of slowly rotating relativistic stars in the
Regge--Wheeler gauge. We demonstrate the stability preperties of the new
evolution set of equations and compute the polar w-modes for slowly rotating
stars.Comment: 27 pages, 2 figure
Tests of the Gravitational Inverse-Square Law below the Dark-Energy Length Scale
We conducted three torsion-balance experiments to test the gravitational
inverse-square law at separations between 9.53 mm and 55 micrometers, probing
distances less than the dark-energy length scale m. We find with 95% confidence
that the inverse-square law holds () down to a length scale
m and that an extra dimension must have a size m.Comment: 4 pages, 6 figure
Universality of massive scalar field late-time tails in black-hole spacetimes
The late-time tails of a massive scalar field in the spacetime of black holes
are studied numerically. Previous analytical results for a Schwarzschild black
hole are confirmed: The late-time behavior of the field as recorded by a static
observer is given by , where
depends weakly on time. This result is carried over to the case of
a Kerr black hole. In particular, it is found that the power-law index of -5/6
depends on neither the multipole mode nor on the spin rate of the black
hole . In all black hole spacetimes, massive scalar fields have the same
late-time behavior irrespective of their initial data (i.e., angular
distribution). Their late-time behavior is universal.Comment: 11 pages, 14 figures, published versio
Testing numerical relativity with the shifted gauge wave
Computational methods are essential to provide waveforms from coalescing
black holes, which are expected to produce strong signals for the gravitational
wave observatories being developed. Although partial simulations of the
coalescence have been reported, scientifically useful waveforms have so far not
been delivered. The goal of the AppleswithApples (AwA) Alliance is to design,
coordinate and document standardized code tests for comparing numerical
relativity codes. The first round of AwA tests have now being completed and the
results are being analyzed. These initial tests are based upon periodic
boundary conditions designed to isolate performance of the main evolution code.
Here we describe and carry out an additional test with periodic boundary
conditions which deals with an essential feature of the black hole excision
problem, namely a non-vanishing shift. The test is a shifted version of the
existing AwA gauge wave test. We show how a shift introduces an exponentially
growing instability which violates the constraints of a standard harmonic
formulation of Einstein's equations. We analyze the Cauchy problem in a
harmonic gauge and discuss particular options for suppressing instabilities in
the gauge wave tests. We implement these techniques in a finite difference
evolution algorithm and present test results. Although our application here is
limited to a model problem, the techniques should benefit the simulation of
black holes using harmonic evolution codes.Comment: Submitted to special numerical relativity issue of Classical and
Quantum Gravit
Analytical solutions for black-hole critical behaviour
Dynamical Einstein cluster is a spherical self-gravitating system of
counterrotating particles, which may expand, oscillate and collapse. This
system exhibits critical behaviour in its collapse at the threshold of black
hole formation. It appears when the specific angular momentum of particles is
tuned finely to the critical value. We find the unique exact self-similar
solution at the threshold. This solution begins with a regular surface,
involves timelike naked singularity formation and asymptotically approaches a
static self-similar cluster.Comment: 4 pages, 3 figures, accepted for publication in General Relativity
and Gravitation, typos correcte
Vacuum induced torque between corrugated metallic plates
We study the torque arising between two corrugated metallic plates due to the
interaction with electromagnetic vacuum. This Casimir torque can be measured
with torsion pendulum techniques for separation distances as large as 1m.
It allows one to probe the nontrivial geometry dependence of the Casimir energy
in a configuration which can be evaluated theoretically with accuracy. In the
optimal experimental configuration, the commonly used proximity force
approximation turns out to overestimate the torque by a factor 2 or larger.Comment: 7 pages, 4 figures, to appear in Europhysics Letters. Technical
problem with eps file for figure 4 was fixe
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