2,389 research outputs found
Spectral changes during six years of Scorpius X-1 monitoring with BeppoSAX Wide Field Cameras
We analyse a sample of fifty-five observations of Scorpius X-1 available in
the BeppoSAX Wide Field Camera public archive and spanning over the six years
of BeppoSAX mission life. Spectral changes are initially analysed by inspection
of colour-colour and colour-intensity diagrams, we also discuss the shift of
the Z tracks in these diagrams. Then we select two long observations for
spectral fitting analysis, a secular shift is evident between the tracks in
these observations. We finally extract spectra along the tracks and discuss the
best fit model, the parameter variations along the track and between tracks,
and their link to the accretion rate.Comment: 6 pages, 11 postscrpt figures.To appear in the conference proceedings
of `Interacting Binaries: Accretion, Evolution & Outcomes' (Cefalu', July
4-10 2004
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
Liquid actuated gravity experiments
We describe a new actuation technique for gravity experiments based on a
liquid field mass. The Characterizing idea is to modulate the gravity force
acting on a test mass by controlling the level of a liquid in a suitable
container. This allows to obtain a periodical gravity force without moving
parts (except the liquid level) close to the TM. We describe in detail the most
relevant aspects of the liquid actuator and discuss how it can be used in
gravity experiments. In particular we analyse an application to test the
inverse square law in the mm to cm distance region
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
Towards weighing the condensation energy to ascertain the Archimedes force of vacuum
The force exerted by the gravitational field on a Casimir cavity in terms of
Archimedes force of vacuum is discussed, the force that can be tested against
observation is identified, and it is shown that the present technology makes it
possible to perform the first experimental tests. The use of suitable high-Tc
superconductors as modulators of Archimedes force is motivated. The possibility
is analyzed of using gravitational wave interferometers as detectors of the
force, transported through an optical spring from the Archimedes vacuum force
apparatus to the gravitational interferometer test masses to maintain the two
systems well separated. The use of balances to actuate and detect the force is
also analyzed, the different solutions are compared, and the most important
experimental issues are discussed.Comment: Revtex, 33 pages, 8 figures. In the final version, the title has been
changed, and all sections have been improved, while 2 appendices have been
adde
A quasi-complete mechanical model for a double torsion pendulum
We present a dynamical model for the double torsion pendulum nicknamed PETER,
where one torsion pendulum hangs in cascade, but off-axis, from the other. The
dynamics of interest in these devices lies around the torsional resonance, that
is at very low frequencies (mHz). However, we find that, in order to properly
describe the forced motion of the pendulums, also other modes must be
considered, namely swinging and bouncing oscillations of the two suspended
masses, that resonate at higher frequencies (Hz). Although the system has
obviously 6+6 Degrees of Freedom, we find that 8 are sufficient for an accurate
description of the observed motion. This model produces reliable estimates of
the response to generic external disturbances and actuating forces or torques.
In particular, we compute the effect of seismic floor motion (tilt noise) on
the low frequency part of the signal spectra and show that it properly accounts
for most of the measured low frequency noise.Comment: 15 pages, 6 figure
Quantum time delay in the gravitational field of a rotating mass
We examine quantum corrections of time delay arising in the gravitational field of a spinning oblate source. Low-energy quantum effects occurring in Kerr geometry are derived within a framework where general relativity is fully seen as an effective field theory. By employing such a pattern, gravitational radiative modifications of Kerr metric are derived from the energy-momentum tensor of the source, which at lowest order in the fields is modelled as a point mass. Therefore, in order to describe a quantum corrected version of time delay in the case in which the source body has a finite extension, we introduce a hybrid scheme where quantum fluctuations affect only the monopole term occurring in the multipole expansion of the Newtonian potential. The predicted quantum deviation from the corresponding classical value turns out to be too small to be detected in the next future, showing that new models should be examined in order to test low-energy quantum gravity within the solar system
Quantum time delay in the gravitational field of a rotating mass
We examine quantum corrections of time delay arising in the gravitational field of a spinning oblate
source. Low-energy quantum effects occurring in Kerr geometry are derived within a framework
where general relativity is fully seen as an effective field theory. By employing such a pattern,
gravitational radiative modifications of Kerr metric are derived from the energy-momentum tensor
of the source, which at lowest order in the fields is modelled as a point mass. Therefore, in order to
describe a quantum corrected version of time delay in the case in which the source body has a finite
extension, we introduce a hybrid scheme where quantum fluctuations affect only the monopole term
occurring in the multipole expansion of the Newtonian potential. The predicted quantum deviation
from the corresponding classical value turns out to be too small to be detected in the next future,
showing that new models should be examined in order to test low-energy quantum gravity within
the solar system
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