1,086 research outputs found
Maximally Symmetric Spin-Two Bitensors on and
The transverse traceless spin-two tensor harmonics on and may be
denoted by . The index labels the (degenerate) eigenvalues
of the Laplacian and the other indices. We compute the bitensor
where are distinct
points on a sphere or hyperboloid of unit radius. These quantities may be used
to find the correlation function of a stochastic background of gravitational
waves in spatially open or closed Friedman-Robertson-Walker cosmologies.Comment: 12 pages, RevTeX, uuencoded compressed .tex file, minor typos
correcte
A rapid screening, âcombinatorial-typeâ survey of the metalloligand chemistry of Ptâ(PPhâ)â(ÎŒ-S)â using electrospray mass spectrometry
Electrospray mass spectrometry is a rapid and powerful technique for a combinatorial-like survey of the chemistry of the metalloligand Ptâ(PPhâ)â(ÎŒ-S)â, leading to the successful isolation and crystallographic characterisation of the novel protonated species Ptâ(PPhâ)â(ÎŒ-S)(ÎŒ-SH) together with a range of metallated derivatives
The Growth of Black Holes and Bulges at the Cores of Cooling Flows
Central cluster galaxies (cDs) in cooling flows are growing rapidly through
gas accretion and star formation. At the same time, AGN outbursts fueled by
accretion onto supermassive black holes are generating X-ray cavity systems and
driving outflows that exceed those in powerful quasars. We show that the
resulting bulge and black hole growth follows a trend that is roughly
consistent with the slope of the local (Magorrian) relation between bulge and
black hole mass for nearby quiescent ellipticals. However, a large scatter
suggests that cD bulges and black holes do not always grow in lock-step. New
measurements made with XMM, Chandra, and FUSE of the condensation rates in
cooling flows are now approaching or are comparable to the star formation
rates, alleviating the need for an invisible sink of cold matter. We show that
the remaining radiation losses can be offset by AGN outbursts in more than half
of the systems in our sample, indicating that the level of cooling and star
formation is regulated by AGN feedback.Comment: 3 pages, 4 figures, to appear in the proceedings of "Heating vs.
Cooling in Galaxies and Clusters of Galaxies," edited by H. Boehringer, P.
Schuecker, G. W. Pratt, and A. Finogueno
Gravitational Waves in Open de Sitter Space
We compute the spectrum of primordial gravitational wave perturbations in
open de Sitter spacetime. The background spacetime is taken to be the
continuation of an O(5) symmetric instanton saddle point of the Euclidean no
boundary path integral. The two-point tensor fluctuations are computed directly
from the Euclidean path integral. The Euclidean correlator is then analytically
continued into the Lorentzian region where it describes the quantum mechanical
vacuum fluctuations of the graviton field. Unlike the results of earlier work,
the correlator is shown to be unique and well behaved in the infrared. We show
that the infrared divergence found in previous calculations is due to the
contribution of a discrete gauge mode inadvertently included in the spectrum.Comment: 17 pages, compressed and RevTex file, including one postscript figure
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Green's function for the Hodge Laplacian on some classes of Riemannian and Lorentzian symmetric spaces
We compute the Green's function for the Hodge Laplacian on the symmetric
spaces M\times\Sigma, where M is a simply connected n-dimensional Riemannian or
Lorentzian manifold of constant curvature and \Sigma is a simply connected
Riemannian surface of constant curvature. Our approach is based on a
generalization to the case of differential forms of the method of spherical
means and on the use of Riesz distributions on manifolds. The radial part of
the Green's function is governed by a fourth order analogue of the Heun
equation.Comment: 18 page
Gravity Waves from Instantons
We perform a first principles computation of the spectrum of gravity waves
produced in open inflationary universes. The background spacetime is taken to
be the continuation of an instanton saddle point of the Euclidean no boundary
path integral. The two-point tensor correlator is computed directly from the
path integral and is shown to be unique and well behaved in the infrared. We
discuss the tensor contribution to the cosmic microwave background anisotropy
and show how it may provide an observational discriminant between different
types of primordial instantons.Comment: 19 pages, RevTex file, including two postscript figure file
Searching for galaxy clusters in the VST-KiDS Survey
We present the methods and first results of the search for galaxy clusters in
the Kilo Degree Survey (KiDS). The adopted algorithm and the criterium for
selecting the member galaxies are illustrated. Here we report the preliminary
results obtained over a small area (7 sq. degrees), and the comparison of our
cluster candidates with those found in the RedMapper and SZ Planck catalogues;
the analysis to a larger area (148 sq. degrees) is currently in progress. By
the KiDS cluster search, we expect to increase the completeness of the clusters
catalogue to z = 0.6-0.7 compared to RedMapper.Comment: 5 pages, 4 figures, to be published in the Proceedings of the
Conference "The Universe of Digital Sky Surveys", Naples, November 25-28 201
A Superluminal Subway: The Krasnikov Tube
The ``warp drive'' metric recently presented by Alcubierre has the problem
that an observer at the center of the warp bubble is causally separated from
the outer edge of the bubble wall. Hence such an observer can neither create a
warp bubble on demand nor control one once it has been created. In addition,
such a bubble requires negative energy densities. One might hope that
elimination of the first problem might ameliorate the second as well. We
analyze and generalize a metric, originally proposed by Krasnikov for two
spacetime dimensions, which does not suffer from the first difficulty. As a
consequence, the Krasnikov metric has the interesting property that although
the time for a one-way trip to a distant star cannot be shortened, the time for
a round trip, as measured by clocks on Earth, can be made arbitrarily short. In
our four dimensional extension of this metric, a ``tube'' is constructed along
the path of an outbound spaceship, which connects the Earth and the star.
Inside the tube spacetime is flat, but the light cones are opened out so as to
allow superluminal travel in one direction. We show that, although a single
Krasnikov tube does not involve closed timelike curves, a time machine can be
constructed with a system of two non-overlapping tubes. Furthermore, it is
demonstrated that Krasnikov tubes, like warp bubbles and traversable wormholes,
also involve unphysically thin layers of negative energy density, as well as
large total negative energies, and therefore probably cannot be realized in
practice.Comment: 20 pages, LATEX, 5 eps figures, uses \eps
Thermodynamic properties, multiphase gas, and AGN feedback in a large sample of giant ellipticals
We present a study of the thermal structure of the hot X-ray emitting
atmospheres for a sample of 49 nearby X-ray and optically bright elliptical
galaxies using {\it Chandra} X-ray data. We focus on the connection between the
properties of the hot X-ray emitting gas and the cooler H+[NII]
emitting phase, and the possible role of the latter in the AGN (Active Galactic
Nuclei) feedback cycle. We do not find evident correlations between the
H+[NII] emission and global properties such as X-ray luminosity, mass
of hot gas, and gas mass fraction. We find that the presence of H+[NII]
emission is more likely in systems with higher densities, lower entropies,
shorter cooling times, shallower entropy profiles, lower values of min(), and disturbed X-ray morphologies (linked to turbulent
motions). However, we see no clear separations in the observables obtained for
galaxies with and without optical emission line nebulae. The AGN jet powers of
the galaxies with X-ray cavities show hint of a possible weak positive
correlation with their H+[NII] luminosities. This correlation and the
observed trends in the thermodynamic properties may result from chaotic cold
accretion (CCA) powering AGN jets, as seen in some high-resolution hydrodynamic
simulations.Comment: Published in MNRA
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