2,271 research outputs found
Sonoluminescence as a QED vacuum effect. II: Finite Volume Effects
In a companion paper [quant-ph/9904013] we have investigated several
variations of Schwinger's proposed mechanism for sonoluminescence. We
demonstrated that any realistic version of Schwinger's mechanism must depend on
extremely rapid (femtosecond) changes in refractive index, and discussed ways
in which this might be physically plausible. To keep that discussion tractable,
the technical computations in that paper were limited to the case of a
homogeneous dielectric medium. In this paper we investigate the additional
complications introduced by finite-volume effects. The basic physical scenario
remains the same, but we now deal with finite spherical bubbles, and so must
decompose the electromagnetic field into Spherical Harmonics and Bessel
functions. We demonstrate how to set up the formalism for calculating Bogolubov
coefficients in the sudden approximation, and show that we qualitatively retain
the results previously obtained using the homogeneous-dielectric (infinite
volume) approximation.Comment: 23 pages, LaTeX 209, ReV-TeX 3.2, five figure
Schwinger's Dynamical Casimir Effect: Bulk Energy Contribution
Schwinger's Dynamical Casimir Effect is one of several candidate explanations
for sonoluminescence. Recently, several papers have claimed that Schwinger's
estimate of the Casimir energy involved is grossly inaccurate. In this letter,
we show that these calculations omit the crucial volume term. When the missing
term is correctly included one finds full agreement with Schwinger's result for
the Dynamical Casimir Effect. We have nothing new to say about sonoluminescence
itself except to affirm that the Casimir effect is energetically adequate as a
candidate explanation.Comment: 6 pages. Uses LaTeX with RevTeX package in two-column forma
Sonoluminescence as a QED vacuum effect: Probing Schwinger's proposal
Several years ago Schwinger proposed a physical mechanism for
sonoluminescence in terms of photon production due to changes in the properties
of the quantum-electrodynamic (QED) vacuum arising from a collapsing dielectric
bubble. This mechanism can be re-phrased in terms of the Casimir effect and has
recently been the subject of considerable controversy. The present paper probes
Schwinger's suggestion in detail: Using the sudden approximation we calculate
Bogolubov coefficients relating the QED vacuum in the presence of the expanded
bubble to that in the presence of the collapsed bubble. In this way we derive
an estimate for the spectrum and total energy emitted. We verify that in the
sudden approximation there is an efficient production of photons, and further
that the main contribution to this dynamic Casimir effect comes from a volume
term, as per Schwinger's original calculation. However, we also demonstrate
that the timescales required to implement Schwinger's original suggestion are
not physically relevant to sonoluminescence. Although Schwinger was correct in
his assertion that changes in the zero-point energy lead to photon production,
nevertheless his original model is not appropriate for sonoluminescence. In
other works (see quant-ph/9805023, quant-ph/9904013, quant-ph/9904018,
quant-ph/9905034) we have developed a variant of Schwinger's model that is
compatible with the physically required timescales.Comment: 18 pages, ReV_TeX 3.2, 9 figures. Major revisions: This document is
now limited to providing a probe of Schwinger's original suggestion for
sonoluminescence. For details on our own variant of Schwinger's ideas see
quant-ph/9805023, quant-ph/9904013, quant-ph/9904018, quant-ph/990503
A modified Schwinger's formula for the Casimir effect
After briefly reviewing how the (proper-time) Schwinger's formula works for
computing the Casimir energy in the case of "scalar electrodynamics" where the
boundary conditions are dictated by two perfectly conducting parallel plates
with separation "a" in the Z-axis, we propose a slightly modification in the
previous approach based on an analytical continuation method. As we will see,
for the case at hand our formula does not need the use of Poisson summation to
get a (renormalized) finite result.Comment: 6 pages, DFTUZ/93/14 (a short version will appear in the Letters in
Math. Phys.
Magnetic Permeability of Constrained Fermionic Vacuum
We obtain using Schwinger's proper time approach the Casimir-Euler-Heisenberg
effective action of fermion fluctuations for the case of an applied magnetic
field. We implement here the compactification of one space dimension into a
circle through anti-periodic boundary condition. Aside of higher order
non-linear field effects we identify a novel contribution to the vacuum
permeability. These contributions are exceedingly small for normal
electromagnetism due to the smallness of the electron Compton wavelength
compared to the size of the compactified dimension, if we take the latter as
the typical size of laboratory cavities, but their presence is thought
provoking, also considering the context of strong interactions.Comment: 8 pages, LaTex, 1 postscript figure, Phys. Let. B in press, slight
text revisions, references adde
THE DYSON-SCHWINGER EQUATION FOR A MODEL WITH INSTANTONS - THE SCHWINGER MODEL
Using the exact path integral solution of the Schwinger model -- a model
where instantons are present -- the Dyson-Schwinger equation is shown to hold
by explicit computation. It turns out that the Dyson-Schwinger equation
separately holds for every instanton sector. This is due to Theta-invariance of
the Schwinger model.Comment: LATEX file 11 pages, no figure
Sonoluminescence as a QED vacuum effect. I: The Physical Scenario
Several years ago Schwinger proposed a physical mechanism for
sonoluminescence in terms of changes in the properties of the
quantum-electrodynamic (QED) vacuum state. This mechanism is most often phrased
in terms of changes in the Casimir Energy: changes in the distribution of
zero-point energies and has recently been the subject of considerable
controversy. The present paper further develops this quantum-vacuum approach to
sonoluminescence: We calculate Bogolubov coefficients relating the QED vacuum
states in the presence of a homogeneous medium of changing dielectric constant.
In this way we derive an estimate for the spectrum, number of photons, and
total energy emitted. We emphasize the importance of rapid spatio-temporal
changes in refractive indices, and the delicate sensitivity of the emitted
radiation to the precise dependence of the refractive index as a function of
wavenumber, pressure, temperature, and noble gas admixture. Although the
physics of the dynamical Casimir effect is a universal phenomenon of QED,
specific experimental features are encoded in the condensed matter physics
controlling the details of the refractive index. This calculation places rather
tight constraints on the possibility of using the dynamical Casimir effect as
an explanation for sonoluminescence, and we are hopeful that this scenario will
soon be amenable to direct experimental probes. In a companion paper we discuss
the technical complications due to finite-size effects, but for reasons of
clarity in this paper we confine attention to bulk effects.Comment: 25 pages, LaTeX 209, ReV-TeX 3.2, eight figures. Minor revisions:
Typos fixed, references updated, minor changes in numerical estimates, minor
changes in some figure
Decay widths and scattering processes in massive QED
Using mass perturbation theory, we infer the bound-state spectrum of massive
QED and compute some decay widths of unstable bound states. Further, we
discuss scattering processes, where all the resonances and particle production
thresholds are properly taken into account by our methods.Comment: Latex file, 5 pages, 8 ps-figures & 1 style-file; written version of
a talk given at the QCD97 conference in Montpellier, Franc
Boundary conditions in local electrostatics algorithms
We study the simulation of charged systems in the presence of general
boundary conditions in a local Monte Carlo algorithm based on a constrained
electric field. We firstly show how to implement constant-potential, Dirichlet,
boundary conditions by introducing extra Monte Carlo moves to the algorithm.
Secondly, we show the interest of the algorithm for studying systems which
require anisotropic electrostatic boundary conditions for simulating planar
geometries such as membranes.Comment: 8 pages, 6 figures, accepted in JC
Quantum radiation in external background fields
A canonical formalism is presented which allows for investigations of quantum
radiation induced by localized, smooth disturbances of classical background
fields by means of a perturbation theory approach. For massless,
non-selfinteracting quantum fields at zero temperature we demonstrate that the
low-energy part of the spectrum of created particles exhibits a non-thermal
character. Applied to QED in varying dielectrics the response theory approach
facilitates to study two distinct processes contributing to the production of
photons: the squeezing effect due to space-time varying properties of the
medium and of the velocity effect due to its motion. The generalization of this
approach to finite temperatures as well as the relation to sonoluminescence is
indicated.Comment: 20 page
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