169 research outputs found
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
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
Probing Gravitational Theories with Eccentric Eclipsing Detached Binary Stars
In this paper, we compare the effects of different theories of gravitation on the apsidal motion of eccentric eclipsing detached binary stars. The comparison is performed by using the formalism of the post-Newtonian parametrization to calculate the theoretical advance at periastron and compare it to the observed one, after having considered the effects of the structure and rotation of the involved stars. A variance analysis on the results of this comparison shows that no signicant difference can be found due to the effect of the different theories under test with respect to the standard general relativity (GR). It will be possible to observe differences, as we would expect, by checking the observed period variation on a much larger lapse of time
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