54,418 research outputs found
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
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
Competition between charge and spin order in the extended Hubbard model on the triangular lattice
Several new classes of compounds can be modeled in first approximation by
electrons on the triangular lattice that interact through on-site repulsion
as well as nearest-neighbor repulsion . This extended Hubbard model on a
triangular lattice has been studied mostly in the strong coupling limit for
only a few types of instabilities. Using the extended two-particle self
consistent approach (ETPSC), that is valid at weak to intermediate coupling, we
present an unbiased study of the density and interaction dependent crossover
diagram for spin and charge density wave instabilities of the normal state at
arbitrary wave vector. When dominates over and electron filling is
large, instabilities are chiefly in the spin sector and are controlled mostly
by Fermi surface properties. Increasing eventually leads to charge
instabilities. In the latter case, it is mostly the wave vector dependence of
the vertex that determines the wave vector of the instability rather than Fermi
surface properties. At small filling, non-trivial instabilities appear only
beyond the weak coupling limit. There again, charge density wave instabilities
are favored over a wide range of dopings by large at wave vectors
corresponding to superlattice in real space.
Commensurate fillings do not play a special role for this instability.
Increasing leads to competition with ferromagnetism. At negative values of
or , neglecting superconducting fluctuations, one finds that charge
instabilities are favored. In general, the crossover diagram presents a rich
variety of instabilities. We also show that thermal charge-density wave
fluctuations in the renormalized classical regime can open a pseudogap in the
single-particle spectral weight, just as spin or superconducting fluctuations
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
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
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)
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
Vacuum polarization near cosmic string in RS2 brane world
Gravitational field of cosmic strings in theories with extra spatial
dimensions must differ significantly from that in the Einstein's theory. This
means that all gravity induced properties of cosmic strings need to be revised
too. Here we consider the effect of vacuum polarization outside a straight
infinitely thin cosmic string embedded in a RS2 brane world. Perturbation
technique combined with the method of dimensional regularization is used to
calculate for a massless scalar field.Comment: 8 pages, RevTeX
Stochastic background from extra-galactic double neutron stars
We present Monte Carlo simulations of the extra galactic population of
inspiralling double neutron stars, and estimate its contribution to the
astrophysical gravitational wave background, in the frequency range of ground
based interferometers, corresponding to the last thousand seconds before the
last stable orbit when more than 96 percent of the signal is released. We show
that sources at redshift z>0.5 contribute to a truly continuous background
which may be detected by correlating third generation interferometers.Comment: 13 pages, 7 figures - proceeding of a talk given at the 11th GWDAW,
to appear in CQ
The Mauna Kea Observatories Near-Infrared Filter Set. I: Defining Optimal 1-5 m Bandpasses
A new MKO-NIR infrared filter set is described, including techniques and
considerations given to designing a new set of bandpasses that are useful at
both mid- and high-altitude sites. These filters offer improved photometric
linearity and in many cases reduced background, as well as preserve good
throughput within the JHKLM atmospheric windows. MKO-NIR filters have already
been deployed with a number of instruments around the world as part of a filter
consortium purchase to reduce the unit cost of filters. Through this effort we
hope to establish, for the first time, a single standard set of infrared
fitlers at as many observatories as possible.Comment: PASP, in press; 32 pages, 11 figures, 3 Table
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