3,150 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
Can the QCD Effective Charge Be Symmetrical in the Euclidean and the Minkowskian Regions?
We study a possible symmetrical behavior of the effective charges defined in
the Euclidean and Minkowskian regions and prove that such symmetry is
inconsistent with the causality principle.Comment: 5 pages, REVTe
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
Casimir Energy for a Spherical Cavity in a Dielectric: Applications to Sonoluminescence
In the final few years of his life, Julian Schwinger proposed that the
``dynamical Casimir effect'' might provide the driving force behind the
puzzling phenomenon of sonoluminescence. Motivated by that exciting suggestion,
we have computed the static Casimir energy of a spherical cavity in an
otherwise uniform material. As expected the result is divergent; yet a
plausible finite answer is extracted, in the leading uniform asymptotic
approximation. This result agrees with that found using zeta-function
regularization. Numerically, we find far too small an energy to account for the
large burst of photons seen in sonoluminescence. If the divergent result is
retained, it is of the wrong sign to drive the effect. Dispersion does not
resolve this contradiction. In the static approximation, the Fresnel drag term
is zero; on the mother hand, electrostriction could be comparable to the
Casimir term. It is argued that this adiabatic approximation to the dynamical
Casimir effect should be quite accurate.Comment: 23 pages, no figures, REVTe
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
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
Leptogenesis from Spin-Gravity Coupling Following Inflation
The energy levels of the left and the right handed neutrinos is split in the
background of gravitational waves generated during inflation which in presence
of lepton number violating interactions gives rise to a net lepton asymmetry at
equilibrium. Lepton number violation is achieved by the same dimension five
operator which gives rise to neutrino masses after electro-weak symmetry
breaking. A net baryon asymmetry of the same magnitude can be generated from
this lepton asymmetry by electroweak sphaleron processes.Comment: Journal version (accepted for publication in Phys. Rev. Lett.
Quantum radiation in a plane cavity with moving mirrors
We consider the electromagnetic vacuum field inside a perfect plane cavity
with moving mirrors, in the nonrelativistic approximation. We show that low
frequency photons are generated in pairs that satisfy simple properties
associated to the plane geometry. We calculate the photon generation rates for
each polarization as functions of the mechanical frequency by two independent
methods: on one hand from the analysis of the boundary conditions for moving
mirrors and with the aid of Green functions; and on the other hand by an
effective Hamiltonian approach. The angular and frequency spectra are discrete,
and emission rates for each allowed angular direction are obtained. We discuss
the dependence of the generation rates on the cavity length and show that the
effect is enhanced for short cavity lengths. We also compute the dissipative
force on the moving mirrors and show that it is related to the total radiated
energy as predicted by energy conservation.Comment: 17 pages, 1 figure, published in Physical Review
Algebraic structure of the Feynman propagator and a new correspondence for canonical transformations
We investigate the algebraic structure of the Feynman propagator with a
general time-dependent quadratic Hamiltonian system. Using the Lie-algebraic
technique we obtain a normal-ordered form of the time-evolution operator, and
then the propagator is easily derived by a simple ``Integration Within Ordered
Product" (IWOP) technique.It is found that this propagator contains a classical
generating function which demonstrates a new correspondence between classical
and quantum mechanics
Hybrid noiseless subsystems for quantum communication over optical fibers
We derive the general structure of noiseless subsystems for optical radiation
contained in a sequence of pulses undergoing collective depolarization in an
optical fiber. This result is used to identify optimal ways to implement
quantum communication over a collectively depolarizing channel, which in
general combine various degrees of freedom, such as polarization and phase,
into joint hybrid schemes for protecting quantum coherence.Comment: 5 pages, 1 figur
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