6,624 research outputs found

### Explicit expression for the photon number emission in synchrotron radiation

An explicit and remarkably simple one-dimensional integral expression is
derived for the mean number of photons emitted per revolution in
synchrotron radiation. The familiar high-energy expression
$5\pi\alpha/\sqrt{3(1-\beta^2)}$, printed repeatedly in the literature, is
found to be inaccurate and only truly asymptotic with relative errors of 160%,
82% for $\beta=0.8$, 0.9, respectively. A new improved high-energy expression
for is given.Comment: LaTeX, 3 pages, no figur

### Sonoluminescence: Bogolubov coefficients for the QED vacuum of a time-dependent dielectric bubble

We extend Schwinger's ideas regarding sonoluminescence by explicitly
calculating the Bogolubov coefficients relating the QED vacuum states
associated with changes in a dielectric bubble. Sudden (non-adiabatic) changes
in the refractive index lead to an efficient production of real photons with a
broadband spectrum, and a high-frequency cutoff that arises from the asymptotic
behaviour of the dielectric constant.Comment: 4 pages, RevTeX, 2 figures (.eps file) included with graphics.sty.
Major revisions: physical scenario clarified, additional numerical estimate

### Casimir energy of dielectric systems

A new formula for the Casimir energy of a dispersive dilute dielectric ball
is discussed. The formula for the Casimir energy of a polarizable particle
situated in a perfectly conducting wedge-shaped cavity is derived by a
path-integral coordinate space method in quantum field theory.Comment: Latex 2e, 4 pages, no figures, a talk given at the International
Meeting "Quantum Gravity and Spectral Geometry" (Naples, Italy, July 2-7,
2001

### Functional treatment of quantum scattering via the dynamical principle

A careful functional treatment of quantum scattering is given using
Schwinger's dynamical principle which involves a functional differentiation
operation applied to a generating functional written in closed form. For long
range interactions, such as for the Coulomb one, it is shown that this
expression may be used to obtain explicitly the asymptotic "free" modified
Green function near the energy shell.Comment: 7 page

### Quantum Corrections to Synchrotron Radiation from Wave-Packet

We calculate the radiated energy to $O(\hbar)$ from a charged wave-packet in
the uniform magnetic field. In the high-speed and weak-field limit, while the
non-commutativity of the system reduces the classical radiation, the additional
corrections originated from the velocity uncertainty of the wave-packet leads
to an enhancement of the radiation.Comment: 7 pages, no figur

### 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. 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

### Relativistic, Causal Description of Quantum Entanglement and Gravity

A possible solution to the problem of providing a spacetime description of
the transmission of signals for quantum entangled states is obtained by using a
bimetric spacetime structure, in which quantum entanglement measurements alter
the structure of the classical relativity spacetime. A bimetric gravity theory
locally has two lightcones, one which describes classical special relativity
and a larger lightcone which allows light signals to communicate quantum
information between entangled states, after a measurement device detects one of
the entangled states. The theory would remove the tension that exists between
macroscopic classical, local gravity and macroscopic nonlocal quantum
mechanics.Comment: 12 pages. LaTex file. 1 figure. Additional text. To be published in
Int. J. Mod. Phys.

### Generally covariant quantization and the Dirac field

Canonical Hamiltonian field theory in curved spacetime is formulated in a
manifestly covariant way. Second quantization is achieved invoking a
correspondence principle between the Poisson bracket of classical fields and
the commutator of the corresponding quantum operators. The Dirac theory is
investigated and it is shown that, in contrast to the case of bosonic fields,
in curved spacetime, the field momentum does not coincide with the generators
of spacetime translations. The reason is traced back to the presence of second
class constraints occurring in Dirac theory. Further, it is shown that the
modification of the Dirac Lagrangian by a surface term leads to a momentum
transfer between the Dirac field and the gravitational background field,
resulting in a theory that is free of constraints, but not manifestly
hermitian.Comment: final version, to appear in Annals Phy

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