224 research outputs found
Radiation from a uniformly accelerating harmonic oscillator
We consider a radiation from a uniformly accelerating harmonic oscillator
whose minimal coupling to the scalar field changes suddenly. The exact time
evolutions of the quantum operators are given in terms of a classical solution
of a forced harmonic oscillator. After the jumping of the coupling constant
there occurs a fast absorption of energy into the oscillator, and then a slow
emission follows. Here the absorbed energy is independent of the acceleration
and proportional to the log of a high momentum cutoff of the field. The emitted
energy depends on the acceleration and also proportional to the log of the
cutoff. Especially, if the coupling is comparable to the natural frequency of
the detector () enormous energies are radiated away
from the oscillator.Comment: 26 pages, 1 eps figure, RevTeX, minor correction in grammar, add a
discussio
Acoustic black holes for relativistic fluids
We derive a new acoustic black hole metric from the Abelian Higgs model. In
the non-relativistic limit, while the Abelian Higgs model becomes the
Ginzburg-Landau model, the metric reduces to an ordinary Unruh type. We
investigate the possibility of using (type I and II) superconductors as the
acoustic black holes. We propose to realize experimental acoustic black holes
by using spiral vortices solutions from the Navier-stokes equation in the
non-relativistic classical fluids.Comment: 16 pages. typos corrected, contents expande
A Liquid Model Analogue for Black Hole Thermodynamics
We are able to characterize a 2--dimensional classical fluid sharing some of
the same thermodynamic state functions as the Schwarzschild black hole. This
phenomenological correspondence between black holes and fluids is established
by means of the model liquid's pair-correlation function and the two-body
atomic interaction potential. These latter two functions are calculated exactly
in terms of the black hole internal (quasilocal) energy and the isothermal
compressibility. We find the existence of a ``screening" like effect for the
components of the liquid.Comment: 20 pages and 6 Encapsulated PostScript figure
Towards a Singularity-Proof Scheme in Numerical Relativity
Progress in numerical relativity has been hindered for 30 years because of
the difficulties of avoiding spacetime singularities in numerical evolution. We
propose a scheme which excises a region inside an apparent horizon containing
the singularity. Two major ingredients of the scheme are the use of a
horizon-locking coordinate and a finite differencing which respects the causal
structure of the spacetime. Encouraging results of the scheme in the spherical
collapse case are given.Comment: 9 page
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Mathematical model of thermal spikes in microwave heating of ceramic oxide fibers
Experiments on microwave sintering of ceramic fibers in a single-mode cavity have revealed the presence of thermal spikes and `hot spots` which sometimes travel along the fiber and eventually disappear. They are triggered by relatively small increases in microwave power, and thus have obvious implications for the development of practical microwave-based fiber processing systems. These hot spots are conjectured to originate at slight irregularities in the tow morphology, and propagate as the result of solid phase transitions which take place at elevated temperatures and reduce the dielectric loss coefficient {epsilon}{double_prime}. An elementary mathematical model of the heat transfer process was developed which reproduces the essential features of the observed phenomena, thus lending support to the conjecture. This model is based on the assumption of one-dimensional heat conduction along the axis of the fiber tow, and radiation losses at the surface
Stochastically Fluctuating Black-Hole Geometry, Hawking Radiation and the Trans-Planckian Problem
We study the propagation of null rays and massless fields in a black hole
fluctuating geometry. The metric fluctuations are induced by a small
oscillating incoming flux of energy. The flux also induces black hole mass
oscillations around its average value. We assume that the metric fluctuations
are described by a statistical ensemble. The stochastic variables are the
phases and the amplitudes of Fourier modes of the fluctuations. By averaging
over these variables, we obtain an effective propagation for massless fields
which is characterized by a critical length defined by the amplitude of the
metric fluctuations: Smooth wave packets with respect to this length are not
significantly affected when they are propagated forward in time. Concomitantly,
we find that the asymptotic properties of Hawking radiation are not severely
modified. However, backward propagated wave packets are dissipated by the
metric fluctuations once their blue shifted frequency reaches the inverse
critical length. All these properties bear many resemblences with those
obtained in models for black hole radiation based on a modified dispersion
relation. This strongly suggests that the physical origin of these models,
which were introduced to confront the trans-Planckian problem, comes from the
fluctuations of the black hole geometry.Comment: 32 page
Quantum Logic with a Single Trapped Electron
We propose the use of a trapped electron to implement quantum logic
operations. The fundamental controlled-NOT gate is shown to be feasible. The
two quantum bits are stored in the internal and external (motional) degrees of
freedom.Comment: 7 Pages, REVTeX, No Figures, To appear in Phys. Rev.
Quantum Geometrodynamics I: Quantum-Driven Many-Fingered Time
The classical theory of gravity predicts its own demise -- singularities. We
therefore attempt to quantize gravitation, and present here a new approach to
the quantization of gravity wherein the concept of time is derived by imposing
the constraints as expectation-value equations over the true dynamical degrees
of freedom of the gravitational field -- a representation of the underlying
anisotropy of space. This self-consistent approach leads to qualitatively
different predictions than the Dirac and the ADM quantizations, and in
addition, our theory avoids the interpretational conundrums associated with the
problem of time in quantum gravity. We briefly describe the structure of our
functional equations, and apply our quantization technique to two examples so
as to illustrate the basic ideas of our approach.Comment: 11, (No Figures), (Typeset using RevTeX
Problem of Time in Quantum Gravity
The Problem of Time occurs because the `time' of GR and of ordinary Quantum
Theory are mutually incompatible notions. This is problematic in trying to
replace these two branches of physics with a single framework in situations in
which the conditions of both apply, e.g. in black holes or in the very early
universe. Emphasis in this Review is on the Problem of Time being multi-faceted
and on the nature of each of the eight principal facets. Namely, the Frozen
Formalism Problem, Configurational Relationalism Problem (formerly Sandwich
Problem), Foliation Dependence Problem, Constraint Closure Problem (formerly
Functional Evolution Problem), Multiple Choice Problem, Global Problem of Time,
Problem of Beables (alias Problem of Observables) and Spacetime
Reconstruction/Replacement Problem. Strategizing in this Review is not just
centred about the Frozen Formalism Problem facet, but rather about each of the
eight facets. Particular emphasis is placed upon A) relationalism as an
underpinning of the facets and as a selector of particular strategies
(especially a modification of Barbour relationalism, though also with some
consideration of Rovelli relationalism). B) Classifying approaches by the full
ordering in which they embrace constrain, quantize, find time/history and find
observables, rather than only by partial orderings such as "Dirac-quantize". C)
Foliation (in)dependence and Spacetime Reconstruction for a wide range of
physical theories, strategizing centred about the Problem of Beables, the
Patching Approach to the Global Problem of Time, and the role of the
question-types considered in physics. D) The Halliwell- and
Gambini-Porto-Pullin-type combined Strategies in the context of semiclassical
quantum cosmology.Comment: Invited Review: 26 pages including 2 Figures. This v2 has a number of
minor improvements and correction
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