65,418 research outputs found
Waveforms for Gravitational Radiation from Cosmic String Loops
We obtain general formulae for the plus- and cross- polarized waveforms of
gravitational radiation emitted by a cosmic string loop in transverse,
traceless (synchronous, harmonic) gauge. These equations are then specialized
to the case of piecewise linear loops, and it is shown that the general
waveform for such a loop is a piecewise linear function. We give several simple
examples of the waveforms from such loops. We also discuss the relation between
the gravitational radiation by a smooth loop and by a piecewise linear
approximation to it.Comment: 16 pages, 6 figures, Revte
The Weyl tensor two-point function in de Sitter spacetime
We present an expression for the Weyl-Weyl two-point function in de Sitter
spacetime, based on a recently calculated covariant graviton two-point function
with one gauge parameter. We find that the Weyl-Weyl two-point function falls
off with distance like r^{-4}, where r is spacelike coordinate separation
between the two points.Comment: 9 pages, no figure
Simultaneous calculation of the helical pitch and the twist elastic constant in chiral liquid crystals from intermolecular torques
We present a molecular simulation method that yields simultaneously the equilibrium pitch wave number q and the twist elastic constant K2 of a chiral nematic liquid crystal by sampling the torque density. A simulation of an untwisted system in periodic boundary conditions gives the product K2q; a further simulation with a uniform twist applied provides enough information to separately determine the two factors. We test our new method for a model potential, comparing the results with K2q from a thermodynamic integration route, and with K2 from an order fluctuation analysis. We also present a thermodynamic perturbation theory analysis valid in the limit of weak chirality
Numerical study of resistivity of model disordered three-dimensional metals
We calculate the zero-temperature resistivity of model 3-dimensional
disordered metals described by tight-binding Hamiltonians. Two different
mechanisms of disorder are considered: diagonal and off-diagonal. The
non-equilibrium Green function formalism provides a Landauer-type formula for
the conductance of arbitrary mesoscopic systems. We use this formula to
calculate the resistance of finite-size disordered samples of different
lengths. The resistance averaged over disorder configurations is linear in
sample length and resistivity is found from the coefficient of proportionality.
Two structures are considered: (1) a simple cubic lattice with one s-orbital
per site, (2) a simple cubic lattice with two d-orbitals. For small values of
the disorder strength, our results agree with those obtained from the Boltzmann
equation. Large off-diagonal disorder causes the resistivity to saturate,
whereas increasing diagonal disorder causes the resistivity to increase faster
than the Boltzmann result. The crossover toward localization starts when the
Boltzmann mean free path relative to the lattice constant has a value between
0.5 and 2.0 and is strongly model dependent.Comment: 4 pages, 5 figure
Spinor Parallel Propagator and Green's Function in Maximally Symmetric Spaces
We introduce the spinor parallel propagator for maximally symmetric spaces in
any dimension. Then, the Dirac spinor Green's functions in the maximally
symmetric spaces R^n, S^n and H^n are calculated in terms of intrinsic
geometric objects. The results are covariant and coordinate-independent.Comment: 7 page
Analytic Results for the Gravitational Radiation from a Class of Cosmic String Loops
Cosmic string loops are defined by a pair of periodic functions and
, which trace out unit-length closed curves in three-dimensional
space. We consider a particular class of loops, for which lies along
a line and lies in the plane orthogonal to that line. For this class
of cosmic string loops one may give a simple analytic expression for the power
radiated in gravitational waves. We evaluate exactly in
closed form for several special cases: (1) a circle traversed
times; (2) a regular polygon with sides and interior vertex angle
; (3) an isosceles triangle with semi-angle .
We prove that case (1) with is the absolute minimum of within
our special class of loops, and identify all the stationary points of
in this class.Comment: 15 pages, RevTex 3.0, 7 figures available via anonymous ftp from
directory pub/pcasper at alpha1.csd.uwm.edu, WISC-MILW-94-TH-1
BRST quantization of the massless minimally coupled scalar field in de Sitter space (zero modes, euclideanization and quantization)
We consider the massless scalar field on the four-dimensional sphere .
Its classical action is degenerate
under the global invariance . We then quantize
the massless scalar field as a gauge theory by constructing a BRST-invariant
quantum action. The corresponding gauge-breaking term is a non-local one of the
form where
is a gauge parameter and is the volume of . It allows us to
correctly treat the zero mode problem. The quantum theory is invariant under
SO(5), the symmetry group of , and the associated two-point functions have
no infrared divergence. The well-known infrared divergence which appears by
taking the massless limit of the massive scalar field propagator is therefore a
gauge artifact. By contrast, the massless scalar field theory on de Sitter
space - the lorentzian version of - is not invariant under the
symmetry group of that spacetime SO(1,4). Here, the infrared divergence is
real. Therefore, the massless scalar quantum field theories on and
cannot be linked by analytic continuation. In this case, because of zero modes,
the euclidean approach to quantum field theory does not work. Similar
considerations also apply to massive scalar field theories for exceptional
values of the mass parameter (corresponding to the discrete series of the de
Sitter group).Comment: This paper has been published under the title "Zero modes,
euclideanization and quantization" [Phys. Rev. D46, 2553 (1992)
A New Waveform Consistency Test for Gravitational Wave Inspiral Searches
Searches for binary inspiral signals in data collected by interferometric
gravitational wave detectors utilize matched filtering techniques. Although
matched filtering is optimal in the case of stationary Gaussian noise, data
from real detectors often contains "glitches" and episodes of excess noise
which cause filter outputs to ring strongly. We review the standard \chi^2
statistic which is used to test whether the filter output has appropriate
contributions from several different frequency bands. We then propose a new
type of waveform consistency test which is based on the time history of the
filter output. We apply one such test to the data from the first LIGO science
run and show that it cleanly distinguishes between true inspiral waveforms and
large-amplitude false signals which managed to pass the standard \chi^2 test.Comment: 10 pages, 6 figures, submitted to Classical and Quantum Gravity for
the proceedings of the Eighth Gravitational Wave Data Analysis Workshop
(GWDAW-8
Is the squeezing of relic gravitational waves produced by inflation detectable?
Grishchuk has shown that the stochastic background of gravitational waves
produced by an inflationary phase in the early Universe has an unusual
property: it is not a stationary Gaussian random process. Due to squeezing, the
phases of the different waves are correlated in a deterministic way, arising
from the process of parametric amplification that created them. The resulting
random process is Gaussian but non-stationary. This provides a unique signature
that could in principle distinguish a background created by inflation from
stationary stochastic backgrounds created by other types of processes. We
address the question: could this signature be observed with a gravitational
wave detector? Sadly, the answer appears to be "no": an experiment which could
distinguish the non-stationary behavior would have to last approximately the
age of the Universe at the time of measurement. This rules out direct detection
by ground and space based gravitational wave detectors, but not indirect
detections via the electromagnetic Cosmic Microwave Background Radiation
(CMBR).Comment: 17 pages, 4 Postscript figures, uses revtex, psfig, to be submitted
to PRD, minor revisions - appendix B clarified, corrected typos, added
reference
Gravitational wave generation in hybrid quintessential inflationary models
We investigate the generation of gravitational waves in the hybrid
quintessential inflationary model. The full gravitational-wave energy spectrum
is calculated using the method of continuous Bogoliubov coefficients. The
post-inflationary kination period, characteristic of quintessential
inflationary models, leaves a clear signature on the spectrum, namely, a peak
at high frequencies. The maximum of the peak is firmly located at the MHz-GHz
region of the spectrum and corresponds to . This
peak is substantially smaller than the one appearing in the gravitational-wave
energy spectrum of the original quintessential inflationary model, therefore
avoiding any conflict with the nucleosynthesis constraint on
\Omega_\Omega_{GW}.Comment: 10 pages, 11 figures, one reference adde
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