5,529 research outputs found
Probing a r-nmodification of the Newtonian potential with exoplanets
The growing availability of increasingly accurate data on transiting exoplanets suggests the possibility of using these systems as possible testbeds for modified models of gravity. In particular, we suggest that the post-Keplerian (pK) dynamical effects from the perturbations of the Newtonian potential falling off as the square or the cube of the distance from the mass of the host star break the degeneracy of the anomalistic, draconitic and sidereal periods. The latter are characteristic temporal intervals in the motion of a binary system, and all coincide in the purely Keplerian case. We work out their analytical expressions in presence of the aforementioned perturbations to yield preliminary insights on the potential of the method proposed for constraining the modified models of gravity considered. A comparison with other results existing in the literature is made
Reference Frames and the Physical Gravito-Electromagnetic Analogy
The similarities between linearized gravity and electromagnetism are known
since the early days of General Relativity. Using an exact approach based on
tidal tensors, we show that such analogy holds only on very special conditions
and depends crucially on the reference frame. This places restrictions on the
validity of the "gravito-electromagnetic" equations commonly found in the
literature.Comment: 9 Pages, 1 figure. To appear in the Proceedings of the IAU Symposium
261 "Relativity in Fundamental Astronomy: Dynamics, Reference Frames, and
Data Analysis", Virginia Beach, USA, 27 April - 1 May 200
Einstein-Cartan theory as a theory of defects in space-time
The Einstein-Cartan theory of gravitation and the classical theory of defects
in an elastic medium are presented and compared. The former is an extension of
general relativity and refers to four-dimensional space-time, while we
introduce the latter as a description of the equilibrium state of a
three-dimensional continuum. Despite these important differences, an analogy is
built on their common geometrical foundations, and it is shown that a
space-time with curvature and torsion can be considered as a state of a
four-dimensional continuum containing defects. This formal analogy is useful
for illustrating the geometrical concept of torsion by applying it to concrete
physical problems. Moreover, the presentation of these theories using a common
geometrical basis allows a deeper understanding of their foundations.Comment: 18 pages, 7 EPS figures, RevTeX4, to appear in the American Journal
of Physics, revised version with typos correcte
Charged Particle Dynamics in the Field of a Slowly Rotating Compact Star
We study the dynamics of a charged particle in the field of a slowly rotating
compact star in the gravitoelectromagnetic approximation to the geodesic
equation . The star is assumed to be surrounded by an ideal, highly conducting
plasma (taken as a magnetohydrodynamic fluid) with a stationary, axially
symmetric electromagnetic field. The general relativistic Maxwell equations are
solved to obtain the effects of the background spacetime on the electromagnetic
field in the linearized Kerr spacetime. The equations of motion are then set up
and solved numerically to incorporate the gravitational as well as the
electromagnetic effects. The analysis shows that in the slow rotation
approximation the frame dragging effects on the electromagnetic field are
absent. However the particle is directly effected by the rotating gravitational
source such that close to the star the gravitational and electromagnetic field
produce contrary effects on the particle's trajectory.Comment: 10 pages, 6 figures in B & W PostScript Forma
Efficiency optimization for Atomic Frequency Comb storage
We study the efficiency of the Atomic Frequency Comb storage protocol. We
show that for a given optical depth, the preparation procedure can be optimize
to significantly improve the retrieval. Our prediction is well supported by the
experimental implementation of the protocol in a \TMYAG crystal. We observe a
net gain in efficiency from 10% to 17% by applying the optimized preparation
procedure. In the perspective of high bandwidth storage, we investigate the
protocol under different magnetic fields. We analyze the effect of the Zeeman
and superhyperfine interaction
Gravitomagnetism in superconductors and compact stars
There are three experimentally observed effects in rotating superconductors
that are so far unexplained. Some authors have tried to interpret such a
phenomena as possible new gravitational properties of coherent quantum systems:
in particular, they suggest that the gravitomagnetic field of that kind of
matter may be many orders of magnitude stronger than the one expected in the
standard theory. Here I show that this interpretation would be in conflict with
the common belief that neutron stars have neutrons in superfluid state and
protons in superconductive one.Comment: 9 pages, no figur
Gravitomagnetic time-varying effects on the motion of a test particle
We study the effects of a time-varying gravitomagnetic field on the motion of
test particles. Starting from recent results, we consider the gravitomagnetic
field of a source whose spin angular momentum has a linearly time-varying
magnitude. The acceleration due to such a time-varying gravitomagnetic field is
considered as a perturbation of the Newtonian motion, and we explicitly
evaluate the effects of this perturbation on the Keplerian elements of a closed
orbit. The theoretical predictions are compared with actual astronomical and
astrophysical scenarios, both in the solar system and in binary pulsars
systems, in order to evaluate the impact of these effects on real systems.Comment: 8 pages, RevTeX; revised to match the version accepted for
publication in General Relativity and Gravitatio
The Lense-Thirring effect in the Jovian system of the Galilean satellites and its measurability
In this paper we investigate the possibility of measuring the post-Newtonian
general relativistic gravitomagnetic Lense-Thirring effect in the Jovian system
of its Galilean satellites Io, Europa, Ganymede and Callisto in view of recent
developments in processing and modelling their optical observations spanning a
large time interval (125 years). The present day best observations have an
accuracy between several kilometers to few tens of kilometers, which is just
the order of magnitude of the Lense-Thirring shifts of the orbits of the
Galilean satellites over almost a century. From a comparison between analytical
development and numerical integration it turns out that, unfortunately, most of
the secular component of the gravitomagnetic signature is removed in the
process of fitting the initial conditions. Indeed, an estimation of the
magnitude of the Lense-Thirring effect in the ephemerides residuals is given;
the resulting residuals have a maximum magnitude of 20 meters only (over 125
years).Comment: Latex, 10 pages, 4 tables, 3 figures, 27 references. Invited paper
for a Special Issue of Int. J. Mod. Phys. D on the Lense-Thirring effect, D.
Grumiller edito
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