4,723 research outputs found
Gravitomagnetism in the Kerr-Newman-Taub-NUT spacetime
We study the motion of test particles and electromagnetic waves in the
Kerr-Newman-Taub-NUT spacetime in order to elucidate some of the effects
associated with the gravitomagnetic monopole moment of the source. In
particular, we determine in the linear approximation the contribution of this
monopole to the gravitational time delay and the rotation of the plane of the
polarization of electromagnetic waves. Moreover, we consider "spherical" orbits
of uncharged test particles in the Kerr-Taub-NUT spacetime and discuss the
modification of the Wilkins orbits due to the presence of the gravitomagnetic
monopole.Comment: 12 pages LaTeX iopart style, uses PicTex for 1 Figur
Electrocardiogram of the Mixmaster Universe
The Mixmaster dynamics is revisited in a new light as revealing a series of
transitions in the complex scale invariant scalar invariant of the Weyl
curvature tensor best represented by the speciality index , which
gives a 4-dimensional measure of the evolution of the spacetime independent of
all the 3-dimensional gauge-dependent variables except for the time used to
parametrize it. Its graph versus time characterized by correlated isolated
pulses in its real and imaginary parts corresponding to curvature wall
collisions serves as a sort of electrocardiogram of the Mixmaster universe,
with each such pulse pair arising from a single circuit or ``complex pulse''
around the origin in the complex plane. These pulses in the speciality index
and their limiting points on the real axis seem to invariantly characterize
some of the so called spike solutions in inhomogeneous cosmology and should
play an important role as a gauge invariant lens through which to view current
investigations of inhomogeneous Mixmaster dynamics.Comment: version 3: 20 pages iopart style, 19 eps figure files for 8 latex
figures; added example of a transient true spike to contrast with the
permanent true spike example from the Lim family of true spike solutions;
remarks in introduction and conclusion adjusted and toned down; minor
adjustments to the remaining tex
Holonomy Transformation in the FRW Metric
In this work we investigate loop variables in Friedman-Robertson-Walker
spacetime. We analyze the parallel transport of vectors and spinors in several
paths in this spacetime in order to classify its global properties. The band
holonomy invariance is analysed in this background.Comment: 8 page
The general relativistic Poynting-Robertson effect
The general relativistic version is developed for Robertson's discussion of
the Poynting-Robertson effect that he based on special relativity and Newtonian
gravity for point radiation sources like stars. The general relativistic model
uses a test radiation field of photons in outward radial motion with zero
angular momentum in the equatorial plane of the exterior Schwarzschild or Kerr
spacetime.Comment: 19 pages iop style, 8 eps figure files for 5 figure
Tracing a relativistic Milky Way within the RAMOD measurement protocol
Advancement in astronomical observations and technical instrumentation
implies taking into account the general relativistic effects due the
gravitational fields encountered by the light while propagating from the star
to the observer. Therefore, data exploitation for Gaia-like space astrometric
mission (ESA, launch 2013) requires a fully relativistic interpretation of the
inverse ray-tracing problem, namely the development of a highly accurate
astrometric models in accordance with the geometrical environment affecting
light propagation itself and the precepts of the theory of measurement. This
could open a new rendition of the stellar distances and proper motions, or even
an alternative detection perspective of many subtle relativistic effects
suffered by light while it is propagating and subsequently recorded in the
physical measurements.Comment: Proceeding for "Relativity and Gravitation, 100 Years after Einstein
in Prague" to be published by Edition Open Access, revised versio
Mechanics of extended masses in general relativity
The "external" or "bulk" motion of extended bodies is studied in general
relativity. Compact material objects of essentially arbitrary shape, spin,
internal composition, and velocity are allowed as long as there is no direct
(non-gravitational) contact with other sources of stress-energy. Physically
reasonable linear and angular momenta are proposed for such bodies and exact
equations describing their evolution are derived. Changes in the momenta depend
on a certain "effective metric" that is closely related to a non-perturbative
generalization of the Detweiler-Whiting R-field originally introduced in the
self-force literature. If the effective metric inside a self-gravitating body
can be adequately approximated by an appropriate power series, the
instantaneous gravitational force and torque exerted on it is shown to be
identical to the force and torque exerted on an appropriate test body moving in
the effective metric. This result holds to all multipole orders. The only
instantaneous effect of a body's self-field is to finitely renormalize the
"bare" multipole moments of its stress-energy tensor. The MiSaTaQuWa expression
for the gravitational self-force is recovered as a simple application. A
gravitational self-torque is obtained as well. Lastly, it is shown that the
effective metric in which objects appear to move is approximately a solution to
the vacuum Einstein equation if the physical metric is an approximate solution
to Einstein's equation linearized about a vacuum background.Comment: 39 pages, 2 figures; fixed equation satisfied by the Green function
used to construct the effective metri
Probing the statistical decay and alpha-clustering effects in 12c+12c and 14n+10b reactions
An experimental campaign has been undertaken at INFN Laboratori Nazionali di
Legnaro, Italy, in order to progress in our understanding of the statistical
properties of light nuclei at excitation energies above particle emission
threshold, by measuring exclusive data from fusion-evaporation reactions. A
first reaction 12C+12C at 7.9 AMeV beam energy has been measured, using the
GARFIELD+Ring Counter experimental setup. Fusion-evaporation events have been
exclusively selected. The comparison to a dedicated Hauser-Feshbach calculation
allows us to give constraints on the nuclear level density at high excitation
energy for light systems ranging from C up to Mg. Out-of-equilibrium emission
has been evidenced and attributed both to entrance channel effects favoured by
the cluster nature of reaction partners and, in more dissipative events, to the
persistence of cluster correlations well above the 24Mg threshold for 6 alphas
decay. The 24Mg compound nucleus has been studied with a new measurement 14N +
10B at 5.7 AMeV. The comparison between the two datasets would allow us to
further constrain the level density of light nuclei. Deviations from a
statistical behaviour can be analyzed to get information on nuclear clustering.Comment: 4 pages, 2 figures, Contribution to conference proceedings of the
25th International Nuclear Physics Conference (INPC 2013
Electromagnetic waves in NUT space: Solutions to the Maxwell equations
In this paper, using the Newman-Penrose formalism, we find the Maxwell
equations in NUT space and after separation into angular and radial components
solve them analytically. All the angular equations are solved in terms of
Jaccobi polynomials. The radial equations are transformed into Hypergeometric
and Heun's equations with the right hand sides including terms of different
order in the frequency of the perturbation which allow solutions in the
expansion of this parameter.Comment: 19 pages, Revtex format, Minor changes including an extention of the
discussion and typos correction, (Extended version of the article presented
to the GR16 conference, July 15-21 2001, Durban, South Africa
Charged black holes: Wave equations for gravitational and electromagnetic perturbations
A pair of wave equations for the electromagnetic and gravitational
perturbations of the charged Kerr black hole are derived. The perturbed
Einstein-Maxwell equations in a new gauge are employed in the derivation. The
wave equations refer to the perturbed Maxwell spinor and to the shear
of a principal null direction of the Weyl curvature. The whole
construction rests on the tripod of three distinct derivatives of the first
curvature of a principal null direction.Comment: 12 pages, to appear in Ap.
GARFIELD + RCo Digital Upgrade: a Modern Set-up for Mass and Charge Identification of Heavy Ion Reaction Products
An upgraded GARFIELD + Ring Counter (RCo) apparatus is presented with
improved performances as far as electronics and detectors are concerned. On one
side fast sampling digital read out has been extended to all detectors,
allowing for an important simplification of the signal processing chain
together with an enriched extracted information. On the other side a relevant
improvement has been made in the forward part of the setup (RCo): an increased
granularity of the CsI(Tl) crystals and a higher homogeneity in the silicon
detector resistivity. The renewed performances of the GARFIELD + RCo array make
it suitable for nuclear reaction measurements both with stable and with
Radioactive Ion Beams (RIB), like the ones foreseen for the SPES facility,
where the Physics of Isospin can be studied.Comment: 13 pages, 19 figures - paper submitted to Eur. Phys. J.
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