360 research outputs found
Colliding Axion-Dilaton Plane Waves from Black Holes
The colliding plane wave metric discovered by Ferrari and Iba\~{n}ez to be
locally isometric to the interior of a Schwarzschild black hole is extended to
the case of general axion-dilaton black holes. Because the transformation maps
either black hole horizon to the focal plane of the colliding waves, this
entire class of colliding plane wave spacetimes only suffers from the formation
of spacetime singularities in the limits where the inner horizon itself is
singular, which occur in the Schwarzschild and dilaton black hole limits. The
supersymmetric limit corresponding to the extreme axion-dilaton black hole
yields the Bertotti-Robinson metric with the axion and dilaton fields flowing
to fixed constant values. The maximal analytic extension of this metric across
the Cauchy horizon yields a spacetime in which two sandwich waves in a
cylindrical universe collide to produce a semi-infinite chain of
Reissner-Nordstrom-like wormholes. The focussing of particle and string
geodesics in this spacetime is explored.Comment: 19 pages, 6 figure
Algebraic approach to quantum field theory on non-globally-hyperbolic spacetimes
The mathematical formalism for linear quantum field theory on curved
spacetime depends in an essential way on the assumption of global
hyperbolicity. Physically, what lie at the foundation of any formalism for
quantization in curved spacetime are the canonical commutation relations,
imposed on the field operators evaluated at a global Cauchy surface. In the
algebraic formulation of linear quantum field theory, the canonical commutation
relations are restated in terms of a well-defined symplectic structure on the
space of smooth solutions, and the local field algebra is constructed as the
Weyl algebra associated to this symplectic vector space. When spacetime is not
globally hyperbolic, e.g. when it contains naked singularities or closed
timelike curves, a global Cauchy surface does not exist, and there is no
obvious way to formulate the canonical commutation relations, hence no obvious
way to construct the field algebra. In a paper submitted elsewhere, we report
on a generalization of the algebraic framework for quantum field theory to
arbitrary topological spaces which do not necessarily have a spacetime metric
defined on them at the outset. Taking this generalization as a starting point,
in this paper we give a prescription for constructing the field algebra of a
(massless or massive) Klein-Gordon field on an arbitrary background spacetime.
When spacetime is globally hyperbolic, the theory defined by our construction
coincides with the ordinary Klein-Gordon field theory on aComment: 21 pages, UCSBTH-92-4
The Effect of Sources on the Inner Horizon of Black Holes
Single pulse of null dust and colliding null dusts both transform a regular
horizon into a space-like singularity in the space of colliding waves. The
local isometry between such space-times and black holes extrapolates these
results to the realm of black holes. However, inclusion of particular scalar
fields instead of null dusts creates null singularities rather than space-like
ones on the inner horizons of black holes.Comment: Final version to appear in PR
Quantum field theory and time machines
We analyze the "F-locality condition" (proposed by Kay to be a mathematical
implementation of a philosophical bias related to the equivalence principle, we
call it the "GH-equivalence principle"), which is often used to build a
generalization of quantum field theory to non-globally hyperbolic spacetimes.
In particular we argue that the theorem proved by Kay, Radzikowski, and Wald to
the effect that time machines with compactly generated Cauchy horizons are
incompatible with the F-locality condition actually does not support the
"chronology protection conjecture", but rather testifies that the F-locality
condition must be modified or abandoned. We also show that this condition
imposes a severe restriction on the geometry of the world (it is just this
restriction that comes into conflict with the existence of a time machine),
which does not follow from the above mentioned philosophical bias. So, one need
not sacrifice the GH-equivalence principle to "emend" the F-locality condition.
As an example we consider a particular modification, the "MF-locality
condition". The theory obtained by replacing the F-locality condition with the
MF-locality condition possesses a few attractive features. One of them is that
it is consistent with both locality and the existence of time machines.Comment: Revtex, 14 pages, 1 .ps figure. To appear in Phys. Rev. D More
detailed discussion is given on the MF-locality condition. Minor corrections
in terminolog
No time machines in classical general relativity
Irrespective of local conditions imposed on the metric, any extendible
spacetime U has a maximal extension containing no closed causal curves outside
the chronological past of U. We prove this fact and interpret it as
impossibility (in classical general relativity) of the time machines, insofar
as the latter are defined to be causality-violating regions created by human
beings (as opposed to those appearing spontaneously).Comment: A corrigendum (to be published in CQG) has been added to correct an
important mistake in the definition of localit
The averaged null energy condition and difference inequalities in quantum field theory
Recently, Larry Ford and Tom Roman have discovered that in a flat cylindrical
space, although the stress-energy tensor itself fails to satisfy the averaged
null energy condition (ANEC) along the (non-achronal) null geodesics, when the
``Casimir-vacuum" contribution is subtracted from the stress-energy the
resulting tensor does satisfy the ANEC inequality. Ford and Roman name this
class of constraints on the quantum stress-energy tensor ``difference
inequalities." Here I give a proof of the difference inequality for a minimally
coupled massless scalar field in an arbitrary two-dimensional spacetime, using
the same techniques as those we relied on to prove ANEC in an earlier paper
with Robert Wald. I begin with an overview of averaged energy conditions in
quantum field theory.Comment: 20 page
From wormhole to time machine: Comments on Hawking's Chronology Protection Conjecture
The recent interest in ``time machines'' has been largely fueled by the
apparent ease with which such systems may be formed in general relativity,
given relatively benign initial conditions such as the existence of traversable
wormholes or of infinite cosmic strings. This rather disturbing state of
affairs has led Hawking to formulate his Chronology Protection Conjecture,
whereby the formation of ``time machines'' is forbidden. This paper will use
several simple examples to argue that the universe appears to exhibit a
``defense in depth'' strategy in this regard. For appropriate parameter regimes
Casimir effects, wormhole disruption effects, and gravitational back reaction
effects all contribute to the fight against time travel. Particular attention
is paid to the role of the quantum gravity cutoff. For the class of model
problems considered it is shown that the gravitational back reaction becomes
large before the Planck scale quantum gravity cutoff is reached, thus
supporting Hawking's conjecture.Comment: 43 pages,ReV_TeX,major revision
“You Can’t Dispose of Mercedes Lightly”: Mercedes de Acosta, Queer Women, and Queer Female Desire in the Early Twentieth Century
This thesis is based off of the life of Mercedes de Acosta (1893-1968), an out lesbian who was very active in the literary, theatrical, and screenwriting spheres at different points in her life. While many could consider her a “failed” artist, given that none of her works were financial successes, she is notable in this time period for the noted quality of her work, her many interpersonal relationships (romantic or otherwise) with others in her trade, and her artistic exploits on both sides of the Atlantic. Being out was incredibly unusual for LGBT+ identified people in this time period, and the homophobia of the period paired with the lack of financial success of her works may have contributed to the fact that she died in poverty. This thesis looks at the life and the historiography of Mercedes de Acosta in an attempt to reconstruct what a lesbian identity meant in this period for women and how her lesbian identity affected both de Acosta\u27s life and her relationships, as well as how she was remembered afterward
The Near-Linear Regime of Gravitational Waves in Numerical Relativity
We report on a systematic study of the dynamics of gravitational waves in
full 3D numerical relativity. We find that there exists an interesting regime
in the parameter space of the wave configurations: a near-linear regime in
which the amplitude of the wave is low enough that one expects the geometric
deviation from flat spacetime to be negligible, but nevertheless where
nonlinearities can excite unstable modes of the Einstein evolution equations
causing the metric functions to evolve out of control. The implications of this
for numerical relativity are discussed.Comment: 10 pages, 2 postscript figures, revised tex
Towards photostatistics from photon-number discriminating detectors
We study the properties of a photodetector that has a number-resolving
capability. In the absence of dark counts, due to its finite quantum
efficiency, photodetection with such a detector can only eliminate the
possibility that the incident field corresponds to a number of photons less
than the detected photon number. We show that such a {\em non-photon}
number-discriminating detector, however, provides a useful tool in the
reconstruction of the photon number distribution of the incident field even in
the presence of dark counts.Comment: 7 pages, 4 figure
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