10,803 research outputs found
Path Integral Over Black Hole Fluctuations
Evaluating a functional integral exactly over a subset of metrics that
represent the quantum fluctuations of the horizon of a black hole, we obtain a
Schroedinger equation in null coordinate time for the key component of the
metric. The equation yields a current that preserves probability if we use the
most natural choice of functional measure. This establishes the existence of
blurred horizons and a thermal atmosphere. It has been argued previously that
the existence of a thermal atmosphere is a direct concomitant of the thermal
radiation of black holes when the temperature of the hole is greater than that
of its larger environment, which we take as zero.Comment: 5 pages, added a couple of clarification
A Survey of Metal Lines at High-redshift (I) : SDSS Absorption Line Studies - The Methodology and First Search Results for OVI
We report the results of a systematic search for signatures of metal lines in
quasar spectra of the Sloan Digital Sky Survey (SDSS) Data Release 3(DR3),
focusing on finding intervening absorbers via detection of their OVI doublet.
Here we present the search algorithm, and criteria for distinguishing
candidates from spurious Lyman {} forest lines. In addition, we compare
our findings with simulations of the Lyman {} forest in order to
estimate the detectability of OVI doublets over various redshift intervals. We
have obtained a sample of 1756 OVI doublet candidates with rest-frame
equivalent width > 0.05 \AA{} in 855 AGN spectra (out of 3702 objects with
redshifts in the accessible range for OVI detection). This sample is further
subdivided into 3 groups according to the likelihood of being real and the
potential for follow-up observation of the candidate. The group with the
cleanest and most secure candidates is comprised of 145 candidates. 69 of these
reside at a velocity separation > 5000 km/s from the QSO, and can therefore be
classified tentatively as intervening absorbers. Most of these absorbers have
not been picked up by earlier, automated QSO absorption line detection
algorithms. This sample increases the number of known OVI absorbers at
redshifts beyond z$_{abs} > 2.7 substantially.Comment: 41 pages, 10 figures, 2 tables, accepted by AJ. This is a
substantially altered version, including an appendix with details on the
validity of the search algorithm on one pixel rather than binning. Also note
that M. Pieri was added as autho
Decoherence induced CPT violation and entangled neutral mesons
We discuss two classes of semi-microscopic theoretical models of stochastic
space-time foam in quantum gravity and the associated effects on entangled
states of neutral mesons, signalling an intrinsic breakdown of CPT invariance.
One class of models deals with a specific model of foam, initially constructed
in the context of non-critical (Liouville) string theory, but viewed here in
the more general context of effective quantum-gravity models. The relevant
Hamiltonian perturbation, describing the interaction of the meson with the foam
medium, consists of off-diagonal stochastic metric fluctuations, connecting
distinct mass eigenstates (or the appropriate generalisation thereof in the
case of K-mesons), and it is proportional to the relevant momentum transfer
(along the direction of motion of the meson pair). There are two kinds of
CPT-violating effects in this case, which can be experimentally disentangled:
one (termed ``omega-effect'') is associated with the failure of the
indistinguishability between the neutral meson and its antiparticle, and
affects certain symmetry properties of the initial state of the two-meson
system; the second effect is generated by the time evolution of the system in
the medium of the space-time foam, and can result in time-dependent
contributions of the $omega-effect type in the time profile of the two meson
state. Estimates of both effects are given, which show that, at least in
certain models, such effects are not far from the sensitivity of experimental
facilities available currently or in the near future. The other class of
quantum gravity models involves a medium of gravitational fluctuations which
behaves like a ``thermal bath''. In this model both of the above-mentioned
intrinsic CPT violation effects are not valid.Comment: 16 pages revtex, no figure
Gauge-invariant variables in general-relativistic perturbations: globalization and zero-mode problem
An outline of a proof of the local decomposition of linear metric
perturbations into gauge-invariant and gauge-variant parts on an arbitrary
background spacetime is briefly explained. We explicitly construct the
gauge-invariant and gauge-variant parts of the linear metric perturbations
based on some assumptions. We also point out the zero-mode problem is an
essential problem to globalize of this decomposition of linear metric
perturbations. The resolution of this zero-mode problem implies the possibility
of the development of the higher-order gauge-invariant perturbation theory on
an arbitrary background spacetime in a global sense.Comment: (v1) 16 pages, no figure; (v2) 9 pages, no figure. Compactified for
"2012 Awards for Essays on Gravitation" promoted by Gravity Research
Foundation. References are deleted. no ingredients is changed. This version
received Honorable Mention for 201
Youth Leadership for Changing Attitudes towards People with Disabilities: Changing Attitudes and Self Esteem
Action and Energy of the Gravitational Field
We present a detailed examination of the variational principle for metric
general relativity as applied to a ``quasilocal'' spacetime region \M (that
is, a region that is both spatially and temporally bounded). Our analysis
relies on the Hamiltonian formulation of general relativity, and thereby
assumes a foliation of \M into spacelike hypersurfaces . We allow for
near complete generality in the choice of foliation. Using a field--theoretic
generalization of Hamilton--Jacobi theory, we define the quasilocal
stress-energy-momentum of the gravitational field by varying the action with
respect to the metric on the boundary \partial\M. The gravitational
stress-energy-momentum is defined for a two--surface spanned by a spacelike
hypersurface in spacetime. We examine the behavior of the gravitational
stress-energy-momentum under boosts of the spanning hypersurface. The boost
relations are derived from the geometrical and invariance properties of the
gravitational action and Hamiltonian. Finally, we present several new examples
of quasilocal energy--momentum, including a novel discussion of quasilocal
energy--momentum in the large-sphere limit towards spatial infinity.Comment: To be published in Annals of Physics. This final version includes two
new sections, one giving examples of quasilocal energy and the other
containing a discussion of energy at spatial infinity. References have been
added to papers by Bose and Dadhich, Anco and Tun
The warp drive: hyper-fast travel within general relativity
It is shown how, within the framework of general relativity and without the
introduction of wormholes, it is possible to modify a spacetime in a way that
allows a spaceship to travel with an arbitrarily large speed. By a purely local
expansion of spacetime behind the spaceship and an opposite contraction in
front of it, motion faster than the speed of light as seen by observers outside
the disturbed region is possible. The resulting distortion is reminiscent of
the ``warp drive'' of science fiction. However, just as it happens with
wormholes, exotic matter will be needed in order to generate a distortion of
spacetime like the one discussed here.Comment: 10 pages, 1 figure. Not previously available in gr-q
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