1,594 research outputs found
Nucleation of vacuum phase transitions by topological defects
The Euclidean action is calculated in the thin-wall approximation for a
first-order vacuum phase transition in which the bubble appears symmetrically
around either a global monopole or a gauge cosmic string. The bubble is assumed
to be much larger than the core size of the monopole or string. In both cases
the value of the Euclidean action is shown to be reduced below the
symmetric action value, indicating that the topological defects act as
effective nucleation sites for vacuum decay.Comment: 10 pages, LaTe
From Wormholes to the Warp Drive: Using theoretical physics to place ultimate bounds on technology
The serious study of such science fiction staples as wormholes, time travel,
and the warp drive, as a means of understanding and constraining possible
realistic solutions within General Relativity is reviewed.Comment: 10 pages LaTeX; to appear in Phi Kappa Phi Foru
Conformal Properties of an Evaporating Black Hole Model
We use a new, conformally-invariant method of analysis to test incomplete
null geodesics approaching the singularity in a model of an evaporating black
hole for the possibility of extensions of the conformal metric. In general, a
local conformal extension is possible from the future but not from the past
Are naked singularites forbidden by the second law of thermodynamics?
By now, many examples of naked singularities in classical general relativity
are known. It may however be that a physical principle over and above the
general theory prevents the occurrence of such singularities in nature.
Assuming the validity of the Weyl curvature hypothesis, we propose that naked
singularities are forbidden by the second law of thermodynamics.Comment: 6 pages, Latex file. This essay was selected for honorable mention by
the Gravity Research Foundatio
Zero temperature black holes in semiclassical gravity
The semiclassical Einstein equations are solved to first order in for the case of an extreme or nearly extreme Reissner-Nordstr\"{o}m
black hole perturbed by the vacuum stress-energy of quantized free fields. It
is shown that, for realistic fields of spin 0, 1/2, or 1, any zero temperature
black hole solution to the equations must have an event horizon at ,
with the charge of the black hole. It is further shown that no black hole
solutions with can be obtained by solving the semiclassical
Einstein equations perturbatively.Comment: 7 pages, to appear in the Proceedings of the Ninth Marcel Grossmann
Meeting, change in titl
Unequal arm space-borne gravitational wave detectors
Unlike ground-based interferometric gravitational wave detectors, large
space-based systems will not be rigid structures. When the end-stations of the
laser interferometer are freely flying spacecraft, the armlengths will change
due to variations in the spacecraft positions along their orbital trajectories,
so the precise equality of the arms that is required in a laboratory
interferometer to cancel laser phase noise is not possible. However, using a
method discovered by Tinto and Armstrong, a signal can be constructed in which
laser phase noise exactly cancels out, even in an unequal arm interferometer.
We examine the case where the ratio of the armlengths is a variable parameter,
and compute the averaged gravitational wave transfer function as a function of
that parameter. Example sensitivity curve calculations are presented for the
expected design parameters of the proposed LISA interferometer, comparing it to
a similar instrument with one arm shortened by a factor of 100, showing how the
ratio of the armlengths will affect the overall sensitivity of the instrument.Comment: 14 pages, 7 figures, REVTeX
Low Frequency Gravitational Waves from Black Hole MACHO Binaries
Nakamura, Sasaki, Tanaka, and Thorne have recently estimated the initial
distribution of binary MACHOs in the galactic halo assuming that the MACHOs are
primordial half solar mass black holes, and considered their coalescence as a
possible source for ground-based interferometer gravitational wave detectors
such as LIGO. Evolving their binary distribution forward in time to the
present, the low-frequency (10^{-5} < f < 10^{-1} Hz) spectrum of gravitational
waves associated with such a population of compact binaries is calculated. The
resulting gravitational waves would form a strong stochastic background in
proposed space interferometers such as LISA and OMEGA. Low frequency
gravitational waves are likely to become a key tool for determining the
properties of binaries within the dark MACHO population.Comment: 8 pages + 2 ps figures; AASTe
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