274 research outputs found
A terrestrial search for dark contents of the vacuum, such as dark energy, using atom interferometry
We describe the theory and first experimental work on our concept for
searching on earth for the presence of dark content of the vacuum (DCV) using
atom interferometry. Specifically, we have in mind any DCV that has not yet
been detected on a laboratory scale, but might manifest itself as dark energy
on the cosmological scale. The experimental method uses two atom
interferometers to cancel the effect of earth's gravity and diverse noise
sources. It depends upon two assumptions: first, that the DCV possesses some
space inhomogeneity in density, and second that it exerts a sufficiently strong
non-gravitational force on matter. The motion of the apparatus through the DCV
should then lead to an irregular variation in the detected matter-wave phase
shift. We discuss the nature of this signal and note the problem of
distinguishing it from instrumental noise. We also discuss the relation of our
experiment to what might be learned by studying the noise in gravitational wave
detectors such as LIGO.The paper concludes with a projection that a future
search of this nature might be carried out using an atom interferometer in an
orbiting satellite. The apparatus is now being constructed
Evaluation of the optimal membrane thickness for direct contact membrane distillation desalination via modelling and experiments
Calibration and analysis of a direct contact membrane distillation (DCMD) model using the GLUE method
On Gravitational Waves in Spacetimes with a Nonvanishing Cosmological Constant
We study the effect of a cosmological constant on the propagation
and detection of gravitational waves. To this purpose we investigate the
linearised Einstein's equations with terms up to linear order in in a
de Sitter and an anti-de Sitter background spacetime. In this framework the
cosmological term does not induce changes in the polarization states of the
waves, whereas the amplitude gets modified with terms depending on .
Moreover, if a source emits a periodic waveform, its periodicity as measured by
a distant observer gets modified. These effects are, however, extremely tiny
and thus well below the detectability by some twenty orders of magnitude within
present gravitational wave detectors such as LIGO or future planned ones such
as LISA.Comment: 8 pages, 4 figures, accepted for publication in Physical Review
Analysis of salinity and membrane thickness influence on a Direct Contract Membrane Distillation module using the Dusty Gas model
A Note on the Integral Formulation of Einstein's Equations Induced on a Braneworld
We revisit the integral formulation (or Green's function approach) of
Einstein's equations in the context of braneworlds. The integral formulation
has been proposed independently by several authors in the past, based on the
assumption that it is possible to give a reinterpretation of the local metric
field in curved spacetimes as an integral expression involving sources and
boundary conditions. This allows one to separate source-generated and
source-free contributions to the metric field. As a consequence, an exact
meaning to Mach's Principle can be achieved in the sense that only
source-generated (matter fields) contributions to the metric are allowed for;
universes which do not obey this condition would be non-Machian. In this paper,
we revisit this idea concentrating on a Randall-Sundrum-type model with a
non-trivial cosmology on the brane. We argue that the role of the surface term
(the source-free contribution) in the braneworld scenario may be quite subtler
than in the 4D formulation. This may pose, for instance, an interesting issue
to the cosmological constant problem.Comment: 10 pages, no figures, accepted for publication in the General
Relativity and Gravitation Journa
On the possibility of measuring the solar oblateness and some relativistic effects from planetary ranging
In this paper we first calculate the post-Newtonian gravitoelectric secular
rate of the mean anomaly of a test particle freely orbiting a spherically
symmetric central mass. Then, we propose a novel approach to suitably combine
the presently available planetary ranging data to Mercury, Venus and Mars in
order to determine, simultaneously and independently of each other, the Sun's
quadrupole mass moment J_2 and the secular advances of the perihelion and the
mean anomaly. This would also allow to obtain the PPN parameters gamma and beta
independently. We propose to analyze the time series of three linear
combinations of the experimental residuals of the rates of the nodes, the
longitudes of perihelia and mean anomalies of Mercury, Venus and Mars built up
in order to absorb the secular precessions induced by the solar oblateness and
the post-Newtonian gravitoelectric forces. The values of the three investigated
parameters can be obtained by fitting the expected linear trends with straight
lines, determining their slopes in arcseconds per century and suitably
normalizing them. According to the present-day EPM2000 ephemerides accuracy,
the obtainable precision would be of the order of 10^-4-10^-5 for the PPN
parameters and, more interestingly, of 10^-9 for J_2. The future BepiColombo
mission should improve the Mercury's orbit by one order of magnitude.Comment: LaTex2e, 11 pages, no figures, 3 tables. Extensively rewritten
version. The role of the classical N-body secular precessions has been
discussed. New observable found for J2. Improved accuracy in it: 10^-9. The
role of BepiColombo discusse
Testing General Relativity with Satellite Laser Ranging: Recent Developments
In this paper the most recent developments in testing General Relativity in
the gravitational field of the Earth with the technique of Satellite Laser
Ranging are presented. In particular, we concentrate our attention on some
gravitoelectric and gravitomagnetic post--Newtonian orbital effects on the
motion of a test body in the external field of a central mass.Comment: Latex2e, 10 pages, no figures, no tables. Paper presented at
COSPAR2002 conference held in Houston, TX, from 10 October 2002 to 19 October
2002. To appear in Advance in Space Research. References added and update
"Cosmological" quasiparticle production in harmonically trapped superfluid gases
We show that a variety of cosmologically motivated effective quasiparticle
space-times can be produced in harmonically trapped superfluid Bose and Fermi
gases. We study the analogue of cosmological particle production in these
effective space-times, induced by trapping potentials and coupling constants
possessing an arbitrary time dependence. The WKB probabilities for phonon
creation from the superfluid vacuum are calculated, and an experimental
procedure to detect quasiparticle production by measuring density-density
correlation functions is proposed.Comment: 8 pages, 1 figure; references updated, as published in Physical
Review
Revisiting Weyl's calculation of the gravitational pull in Bach's two-body solution
When the mass of one of the two bodies tends to zero, Weyl's definition of
the gravitational force in an axially symmetric, static two-body solution can
be given an invariant formulation in terms of a force four-vector. The norm of
this force is calculated for Bach's two-body solution, that is known to be in
one-to-one correspondence with Schwarzschild's original solution when one of
the two masses l, l' is made to vanish. In the limit when, say, l' goes to
zero, the norm of the force divided by l' and calculated at the position of the
vanishing mass is found to coincide with the norm of the acceleration of a test
body kept at rest in Schwarzschild's field. Both norms happen thus to grow
without limit when the test body (respectively the vanishing mass l') is kept
at rest in a position closer and closer to Schwarzschild's two-surface.Comment: 11 pages, 2 figures. Text to appear in Classical and Quantum Gravit
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