23 research outputs found
Simple solutions to the Einstein Equations in spaces with unusual topology
We discuss simple vacuum solutions to the Einstein Equations in five
dimensional space-times compactified in two different ways. In such spaces, one
black hole phase and more then one black string phase may exist. Several old
metrics are adapted to new background topologies to yield new solutions to the
Einstein Equations. We then briefly talk about the angular momentum they may
carry, the horizon topology and phase transitions that may occur.Comment: Published versions. Includes referee input. 10 pages, 3 figure
The Potential of Continuous, Local Atomic Clock Measurements for Earthquake Prediction and Volcanology
Modern optical atomic clocks along with the optical fiber technology
currently being developed can measure the geoid, which is the equipotential
surface that extends the mean sea level on continents, to a precision that
competes with existing technology. In this proceeding, we point out that atomic
clocks have the potential to not only map the sea level surface on continents,
but also look at variations of the geoid as a function of time with
unprecedented timing resolution. The local time series of the geoid has a
plethora of applications. These include potential improvement in the
predictions of earthquakes and volcanoes, and closer monitoring of ground
uplift in areas where hydraulic fracturing is performed.Comment: 7 pages, one figure, proceeding for ICNFP 201
Numerical Simulations of Oscillating Soliton Stars: Excited States in Spherical Symmetry and Ground State Evolutions in 3D
Excited state soliton stars are studied numerically for the first time. The
stability of spherically symmetric S-branch excited state oscillatons under
radial perturbations is investigated using a 1D code. We find that these stars
are inherently unstable either migrating to the ground state or collapsing to
black holes. Higher excited state configurations are observed to cascade
through intermediate excited states during their migration to the ground state.
This is similar to excited state boson stars. Ground state oscillatons are then
studied in full 3D numerical relativity. Finding the appropriate gauge
condition for the dynamic oscillatons is much more challenging than in the case
of boson stars. Different slicing conditions are explored, and a customized
gauge condition that approximates polar slicing in spherical symmetry is
implemented. Comparisons with 1D results and convergence tests are performed.
The behavior of these stars under small axisymmetric perturbations is studied
and gravitational waveforms are extracted. We find that the gravitational waves
damp out on a short timescale, enabling us to obtain the complete waveform.
This work is a starting point for the evolution of real scalar field systems
with arbitrary symmetries.Comment: 12 pages, 11 figures, typos corrected, includes referee input,
references corrected, published versio
A New Family of Light Beams and Mirror Shapes for Future LIGO Interferometers
Advanced LIGO's present baseline design uses arm cavities with Gaussian light
beams supported by spherical mirrors. Because Gaussian beams have large
intensity gradients in regions of high intensity, they average poorly over
fluctuating bumps and valleys on the mirror surfaces, caused by random thermal
fluctuations (thermoelastic noise). Flat-topped light beams (mesa beams) are
being considered as an alternative because they average over the thermoelastic
fluctuations much more effectively. However, the proposed mesa beams are
supported by nearly flat mirrors, which experience a very serious tilt
instability. In this paper we propose an alternative configuration in which
mesa-shaped beams are supported by nearly concentric spheres, which experience
only a weak tilt instability. The tilt instability is analyzed for these
mirrors in a companion paper by Savov and Vyatchanin. We also propose a
one-parameter family of light beams and mirrors in which, as the parameter
alpha varies continuously from 0 to pi, the beams and supporting mirrors get
deformed continuously from the nearly flat-mirrored mesa configuration ("FM")
at alpha=0, to the nearly concentric-mirrored mesa configuration ("CM") at
alpha=pi. The FM and CM configurations at the endpoints are close to optically
unstable, and as alpha moves away from 0 or pi, the optical stability improves.Comment: Submitted to Physical Review D on 21 September 2004; RevTeX, 6 pages,
4 Figure
Atomic clocks as a tool to monitor vertical surface motion
Atomic clock technology is advancing rapidly, now reaching stabilities of
, which corresponds to resolving cm in equivalent
geoid height over an integration timescale of about 7 hours. At this level of
performance, ground-based atomic clock networks emerge as a tool for monitoring
a variety of geophysical processes by directly measuring changes in the
gravitational potential. Vertical changes of the clock's position due to
magmatic, volcanic, post-seismic or tidal deformations can result in measurable
variations in the clock tick rate. As an example, we discuss the geopotential
change arising due to an inflating point source (Mogi model), and apply it to
the Etna volcano. Its effect on an observer on the Earth's surface can be
divided into two different terms: one purely due to uplift and one due to the
redistribution of matter. Thus, with the centimetre-level precision of current
clocks it is already possible to monitor volcanoes. The matter redistribution
term is estimated to be 2-3 orders of magnitude smaller than the uplift term,
and should be resolvable when clocks improve their stability to the
sub-millimetre level. Additionally, clocks can be compared over distances of
thousands of kilometres on a short-term basis (e.g. hourly). These clock
networks will improve our ability to monitor periodic effects with
long-wavelength like the solid Earth tide.Comment: 11 pages, 5 figures, accepted as express letter in the Geophysical
Journal Internationa
Finite Mirror Effects in Advanced Interferometric Gravitational Wave Detectors
Thermal noise is expected to be the dominant source of noise in the most
sensitive frequency band of second generation ground based gravitational wave
detectors. Reshaping the beam to a flatter wider profile which probes more of
the mirror surface reduces this noise. The "Mesa" beam shape has been proposed
for this purpose and was subsequently generalized to a family of hyperboloidal
beams with two parameters: twist angle alpha and beam width D. Varying alpha
allows a continuous transition from the nearly-flat to the nearly-concentric
Mesa beam configurations. We analytically prove that in the limit of infinite D
hyperboloidal beams become Gaussians. The Advanced LIGO diffraction loss design
constraint is 1 ppm per bounce. In the past the diffraction loss has often been
calculated using the clipping approximation that, in general, underestimates
the diffraction loss. We develop a code using pseudo-spectral methods to
compute the diffraction loss directly from the propagator. We find that the
diffraction loss is not a strictly monotonic function of beam width, but has
local minima that occur due to finite mirror effects and leads to natural
choices of D. For the Mesa beam a local minimum occurs at D = 10.67 cm and
leads to a diffraction loss of 1.4 ppm. We find that if one requires a
diffraction loss of strictly 1 ppm, the alpha = 0.91 pi hyperboloidal beam is
optimal, leading to the coating thermal noise being lower by about 10% than for
a Mesa beam while other types of thermal noise decrease as well. We then
develop an iterative process that reconstructs the mirror to specifically
account for finite mirror effects. This allows us to increase the D parameter
and lower the coating noise by about 30% compared to the original Mesa
configuration.Comment: 13 pages, 12 figures, 4 tables. Referee input included and typos
fixed. Accepted by Phys. Rev.