7,574 research outputs found
High Luminosity Issues for DAPhNE Upgrade
We give an overview of presentations and discussions during the Accelerator
Working Group Session dedicated to High Luminosity Issues for a future upgrade
of the Frascati e+e- Phi-Factory DAPhNE at the Workshop "e+e- in the 1-2 GeV
range: Physics and Accelerator Prospects" held at Alghero (Italy) on 10-13
September 2003.Comment: Invited talk at the Workshop on e+e- in the 1-2 GeV range, Alghero,
Italy, September 2003 (eConf c0309101
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
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
Pulsars as celestial beacons to detect the motion of the Earth
In order to show the principle viability of a recently proposed relativistic
positioning method based on the use of pulsed signals from sources at infinity,
we present an application example reconstructing the world-line of an idealized
Earth in the reference frame of distant pulsars. The method considers the null
four-vectors built from the period of the pulses and the direction cosines of
the propagation from each source. Starting from a simplified problem (a
receiver at rest) we have been able to calibrate our procedure, evidencing the
influence of the uncertainty on the arrival times of the pulses as measured by
the receiver, and of the numerical treatment of the data. The most relevant
parameter turns out to be the accuracy of the clock used by the receiver.
Actually the uncertainty used in the simulations combines both the accuracy of
the clock and the fluctuations in the sources. As an evocative example the
method has then been applied to the case of an ideal observer moving as a point
on the surface of the Earth. The input have been the simulated arrival times of
the signals from four pulsars at the location of the Parkes radiotelescope in
Australia. Some substantial simplifications have been made both excluding the
problems of visibility due to the actual size of the planet, and the behaviour
of the sources. A rough application of the method to a three days run gives a
correct result with a poor accuracy. The accuracy is then enhanced to the order
of a few hundred meters if a continuous set of data is assumed. The method
could actually be used for navigation across the solar system and be based on
artificial sources, rather than pulsars. The viability of the method, whose
additional value is in the self-sufficiency, i.e. independence from any control
from other operators, has been confirmed.Comment: 11 pages, 3 eps figures; revised to match the version accepted for
publication in IJMP
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
A post-Keplerian parameter to test gravito-magnetic effects in binary pulsar systems
We study the pulsar timing, focusing on the time delay induced by the
gravitational field of the binary systems. In particular, we study the
gravito-magnetic correction to the Shapiro time delay in terms of Keplerian and
post-Keplerian parameters, and we introduce a new post-Keplerian parameter
which is related to the intrinsic angular momentum of the stars. Furthermore,
we evaluate the magnitude of these effects for the binary pulsar systems known
so far. The expected magnitude is indeed small, but the effect is important per
se.Comment: 6 pages, RevTeX, 1 eps figure, accepted for publication in Physical
Review D; references adde
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
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