2,266 research outputs found
LIGO's "Science Reach"
Technical discussions of the Laser Interferometer Gravitational Wave
Observatory (LIGO) sensitivity often focus on its effective sensitivity to
gravitational waves in a given band; nevertheless, the goal of the LIGO Project
is to ``do science.'' Exploiting this new observational perspective to explore
the Universe is a long-term goal, toward which LIGO's initial instrumentation
is but a first step. Nevertheless, the first generation LIGO instrumentation is
sensitive enough that even non-detection --- in the form of an upper limit ---
is also informative. In this brief article I describe in quantitative terms
some of the science we can hope to do with first and future generation LIGO
instrumentation: it short, the ``science reach'' of the detector we are
building and the ones we hope to build.Comment: 13 pages, including 1 inlined figure
No statistical excess in Explorer/Nautilus observations in the year 2001
A recent report on gravitational wave detector data from the NAUTILUS and
EXPLORER detector groups claims a statistically significant excess of
coincident events when the detectors are oriented in a way that maximizes their
sensitivity to gravitational wave sources in the galactic plane. While not
claiming a detection of gravitational waves, they do strongly suggest that the
origin of the excess is of gravitational wave origin. In this note we show that
the statistical analysis that led them to the conclusion that there is a
statistical excess is flawed and that the reported observation is entirely
consistent with the normal Poisson statistics of the reported detector
background.Comment: 11 pages, 3 figures, to appear in CQ
Spectral Methods for Numerical Relativity. The Initial Data Problem
Numerical relativity has traditionally been pursued via finite differencing.
Here we explore pseudospectral collocation (PSC) as an alternative to finite
differencing, focusing particularly on the solution of the Hamiltonian
constraint (an elliptic partial differential equation) for a black hole
spacetime with angular momentum and for a black hole spacetime superposed with
gravitational radiation. In PSC, an approximate solution, generally expressed
as a sum over a set of orthogonal basis functions (e.g., Chebyshev
polynomials), is substituted into the exact system of equations and the
residual minimized. For systems with analytic solutions the approximate
solutions converge upon the exact solution exponentially as the number of basis
functions is increased. Consequently, PSC has a high computational efficiency:
for solutions of even modest accuracy we find that PSC is substantially more
efficient, as measured by either execution time or memory required, than finite
differencing; furthermore, these savings increase rapidly with increasing
accuracy. The solution provided by PSC is an analytic function given
everywhere; consequently, no interpolation operators need to be defined to
determine the function values at intermediate points and no special
arrangements need to be made to evaluate the solution or its derivatives on the
boundaries. Since the practice of numerical relativity by finite differencing
has been, and continues to be, hampered by both high computational resource
demands and the difficulty of formulating acceptable finite difference
alternatives to the analytic boundary conditions, PSC should be further pursued
as an alternative way of formulating the computational problem of finding
numerical solutions to the field equations of general relativity.Comment: 15 pages, 5 figures, revtex, submitted to PR
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