202 research outputs found
Push on a Casimir apparatus in a weak gravitational field
The influence of the gravity acceleration on the regularized energy-momentum
tensor of the quantized electromagnetic field between two plane parallel
conducting plates is derived. We use Fermi coordinates and work to first order
in the constant acceleration parameter. A new simple formula for the trace
anomaly is found to first order in the constant acceleration, and a more
systematic derivation is therefore obtained of the theoretical prediction
according to which the Casimir device in a weak gravitational field will
experience a tiny push in the upwards direction.Comment: 14 pages, Plain Tex. Talk given at the 17th SIGRAV Conference on
General Relativity and Gravitational Physics, Torino, September 200
Variations of Casimir energy from a superconducting transition
We consider a five-layer Casimir cavity, including a thin superconducting
film. We show that when the cavity is cooled below the critical temperature for
the onset of superconductivity, the sharp variation (in the microwave region)
of the reflection coefficient of the film produces a variation in the value of
the Casimir energy. Even though the relative variation in the Casimir energy is
very small, its magnitude can be comparable to the condensation energy of the
superconducting film, and thus causes a significant increase in the value of
the critical magnetic field, required to destroy the superconductivity of the
film. The proposed scheme might also help clarifying the current controversy
about the magnitude of the contribution to Casimir free energy from the TE zero
mode, as we find that alternative treatments of this mode strongly affect the
shift of critical field.Comment: RevTex 4, 15 pages, 8 figures. Revised version with improved
presentation, a brief description of the ALADIN experiment, and a few
references adde
Towards measuring variations of Casimir energy by a superconducting cavity
We consider a Casimir cavity, one plate of which is a thin superconducting
film. We show that when the cavity is cooled below the critical temperature for
the onset of superconductivity, the sharp variation (in the far infrared) of
the reflection coefficient of the film engenders a variation in the value of
the Casimir energy. Even though the relative variation in the Casimir energy is
very small, its magnitude can be comparable to the condensation energy of the
superconducting film, and this gives rise to a number of testable effects,
including a significant increase in the value of the critical magnetic field,
required to destroy the superconductivity of the film. The theoretical ground
is therefore prepared for the first experiment ever aimed at measuring
variations of the Casimir energy itself.Comment: 4 pages, 2 figures. Substantial improvement of presentation, choice
of a more convenient cavity geometry. Accepted for publication in Phys. Rev.
Let
On the photon Green functions in curved space-time
Quantization of electrodynamics in curved space-time in the Lorenz gauge and
with arbitrary gauge parameter makes it necessary to study Green functions of
non-minimal operators with variable coefficients. Starting from the integral
representation of photon Green functions, we link them to the evaluation of
integrals involving Gamma functions. Eventually, the full asymptotic expansion
of the Feynman photon Green function at small values of the world function, as
well as its explicit dependence on the gauge parameter, are obtained without
adding by hand a mass term to the Faddeev--Popov Lagrangian. Coincidence limits
of second covariant derivatives of the associated Hadamard function are also
evaluated, as a first step towards the energy-momentum tensor in the
non-minimal case.Comment: 22 pages, plain Tex. All sections and appendices have been improve
The gravity of magnetic stresses and energy
In the framework of designing laboratory tests of relativistic gravity, we
investigate the gravitational field produced by the magnetic field of a
solenoid. Observing this field might provide a mean of testing whether stresses
gravitate as predicted by Einstein's theory. A previous study of this problem
by Braginsky, Caves and Thorne predicted that the contribution to the
gravitational field resulting from the stresses of the magnetic field and of
the solenoid walls would cancel the gravitational field produced by the
mass-energy of the magnetic field, resulting in a null magnetically-generated
gravitational force outside the solenoid. They claim that this null result,
once proved experimentally, would demonstrate the stress contribution to
gravity. We show that this result is incorrect, as it arises from an incomplete
analysis of the stresses, which neglects the axial stresses in the walls. Once
the stresses are properly evaluated, we find that the gravitational field
outside a long solenoid is in fact independent of Maxwell and material
stresses, and it coincides with the newtonian field produced by the linear mass
distribution equivalent to the density of magnetic energy stored in a unit
length of the solenoid. We argue that the gravity of Maxwell stress can be
directly measured in the vacuum region inside the solenoid, where the newtonian
noise is absent in principle, and the gravity generated by Maxwell stresses is
not screened by the negative gravity of magnetic-induced stresses in the
solenoid walls.Comment: 10 pages, final version accepted for publication in PR
The Aladin2 experiment: status and perspectives
Aladin2 is an experiment devoted to the first measurement of variations of
Casimir energy in a rigid cavity. The main scientific motivation relies on the
possibility of the first demonstration of a phase transition influenced by
vacuum fluctuations. The guiding principle of the measurement, based on the
behaviour of the critical field for an in-cavity superconducting film, will be
only briefly recalled. In this paper, after an introduction to the long term
motivations, the experimental apparatus and the results of the first
measurement of sensitivity will be presented in detail, particularly in
comparison with the expected signal. Last, the most important steps towards the
final measurement will be discussed.Comment: Talk given by Calloni at QFEXT05 Conference in Barcelona: Quantum
Field Theory Under the Influence of External Condition
Feasibility of a magnetic suspension for second generation Gravitational Wave interferometers
This paper deals with the use of a magnetic levitation system as a part of a
multi-stage seismic attenuator for gravitational wave interferometric antennas.
The proposed configuration uses permanent magnets in attraction to balance the
suspended weight, plus a closed loop position control to obtain a stable
levitation. The system is analyzed using a MATLAB simulation code to compute
the forces exerted by extended magnets. The validity of this model has been
tested by a comparison with the experimental data from a levitated suspension
prototype.Comment: Accepted for publication in Astroparticle Physic
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