3,725 research outputs found
Giant Arc Statistics and Cosmological Parameters
We study with semi-analytical methods the statistics of pronounced arcs
caused by lensing of galaxies by foreground galaxy clusters. For the number
density and redshift distribution of rich clusters we use Press-Schechter
theory, normalized on the basis of empirical data. For the background sources
we make use of observational results in the Hubble Deep Field. We present
results for three different lens models, in particular for the universal
profile suggested by Navarro, Frenk and White. Our primary concern is the
dependence of the expected statistics on the cosmological parameters,
, . The theoretical estimates are compared with the
cluster arcs survey EMSS, and the resulting constraints in the -plane
are presented. In spite of considerable theoretical an observational
uncertainties a low-density universe is favored. Degeneracy curves for the
optical depth and likelihood regions for the arc statistics in the
-plane depend only weakly on the cosmological constant.Comment: Presented at the Journees Relativistes 1999, Weimar (September 12-17
Questioning the Equivalence Principle
The Equivalence Principle (EP) is not one of the ``universal'' principles of
physics (like the Action Principle). It is a heuristic hypothesis which was
introduced by Einstein in 1907, and used by him to construct his theory of
General Relativity. In modern language, the (Einsteinian) EP consists in
assuming that the only long-range field with gravitational-strength couplings
to matter is a massless spin-2 field. Modern unification theories, and notably
String Theory, suggest the existence of new fields (in particular, scalar
fields: ``dilaton'' and ``moduli'') with gravitational-strength couplings. In
most cases the couplings of these new fields ``violate'' the EP. If the field
is long-ranged, these EP violations lead to many observable consequences
(variation of ``constants'', non-universality of free fall, relative drift of
atomic clocks,...). The best experimental probe of a possible violation of the
EP is to compare the free-fall acceleration of different materials.Comment: 14 pages, contribution to the ONERA workshop on "Missions spatiales
en physique fondamentale" (Chatillon, 18-19 Jan 2001), to appear in a special
issue of the Comptes Rendus de l'Academie des Sciences (Paris), edited by C.
Borde and P. Toubou
Dimensional regularization of the gravitational interaction of point masses
We show how to use dimensional regularization to determine, within the
Arnowitt-Deser-Misner canonical formalism, the reduced Hamiltonian describing
the dynamics of two gravitationally interacting point masses. Implementing, at
the third post-Newtonian (3PN) accuracy, our procedure we find that dimensional
continuation yields a finite, unambiguous (no pole part) 3PN Hamiltonian which
uniquely determines the heretofore ambiguous ``static'' parameter: namely,
. Our work also provides a remarkable check of the perturbative
consistency (compatibility with gauge symmetry) of dimensional continuation
through a direct calculation of the ``kinetic'' parameter , giving
the unique answer compatible with global Poincar\'e invariance
() by summing different dimensionally continued
contributions.Comment: REVTeX, 8 pages, 1 figure; submitted to Phys. Lett.
Effective action approach to higher-order relativistic tidal interactions in binary systems and their effective one body description
The gravitational-wave signal from inspiralling neutron-star--neutron-star
(or black-hole--neutron-star) binaries will be influenced by tidal coupling in
the system. An important science goal in the gravitational-wave detection of
these systems is to obtain information about the equation of state of neutron
star matter via the measurement of the tidal polarizability parameters of
neutron stars. To extract this piece of information will require to have
accurate analytical descriptions of both the motion and the radiation of
tidally interacting binaries. We improve the analytical description of the late
inspiral dynamics by computing the next-to-next-to-leading order relativistic
correction to the tidal interaction energy. Our calculation is based on an
effective-action approach to tidal interactions, and on its transcription
within the effective-one-body formalism. We find that second-order relativistic
effects (quadratic in the relativistic gravitational potential ) significantly increase the effective tidal polarizability of
neutron stars by a distance-dependent amplification factor of the form where, say for an equal-mass binary,
(as previously known) and (as
determined here for the first time). We argue that higher-order relativistic
effects will lead to further amplification, and we suggest a Pad\'e-type way of
resumming them. We recommend to test our results by comparing
resolution-extrapolated numerical simulations of inspiralling-binary neutron
stars to their effective one body description.Comment: 29 pages, Physical Review D, to appea
Orbital Tests of Relativistic Gravity using Artificial Satellites
We reexamine non-Einsteinian effects observable in the orbital motion of
low-orbit artificial Earth satellites. The motivations for doing so are
twofold: (i) recent theoretical studies suggest that the correct theory of
gravity might contain a scalar contribution which has been reduced to a small
value by the effect of the cosmological expansion; (ii) presently developed
space technologies should soon give access to a new generation of satellites
endowed with drag-free systems and tracked in three dimensions at the
centimeter level. Our analysis suggests that such data could measure two
independent combinations of the Eddington parameters (beta - 1) and (gamma - 1)
at the 10^-4 level and probe the time variability of Newton's "constant" at the
d(ln G)/dt ~ 10^-13 yr^-1 level. These tests would provide well-needed
complements to the results of the Lunar Laser Ranging experiment, and of the
presently planned experiments aiming at measuring (gamma -1). In view of the
strong demands they make on the level of non- gravitational perturbations,
these tests might require a dedicated mission consisting of an optimized
passive drag-free satellite.Comment: 17 pages, IHES/P/94/22 and CPT-94/P.E.302
A characteristic observable signature of preferred frame effects in relativistic binary pulsars
In this paper we develop a consistent, phenomenological methodology to
measure preferred-frame effects (PFEs) in binary pulsars that exhibit a high
rate of periastron advance. We show that in these systems the existence of a
preferred frame for gravity leads to an observable characteristic `signature'
in the timing data, which uniquely identifies this effect. We expand the
standard Damour-Deruelle timing formula to incorporate this `signature' and
show how this new PFE timing model can be used to either measure or constrain
the parameters related to a violation of the local Lorentz invariance of
gravity in the strong internal fields of neutron stars. In particular, we
demonstrate that in the presence of PFEs we expect a set of the new timing
parameters to have a unique relationship that can be measured and tested
incontrovertibly. This new methodology is applied to the Double Pulsar, which
turns out to be the ideal test system for this kind of experiments.The
currently available dataset allows us only to study the impact of PFEs on the
orbital precession rate, d omega/dt, providing limits that are, at the moment,
clearly less stringent than existing limits on PFE strong-field parameters.
However, simulations show that the constraints improve fast in the coming
years, allowing us to study all new PFE timing parameters and to check for the
unique relationship between them. Finally, we show how a combination of several
suitable systems in a "PFE antenna array", expected to be availabe for instance
with the Square-Kilometre-Array (SKA), provides full sensitivity to possible
violations of local Lorentz invariance in strong gravitational fields in all
directions of the sky. This PFE antenna array may eventually allow us to
determine the direction of a preferred frame should it exist.Comment: Accepted for publication in MNRAS, 12 pages, 5 figures, figures 3 and
5 in reduced quality due to size limitation
Conservation laws for systems of extended bodies in the first post-Newtonian approximation.
The general form of the global conservation laws for -body systems in the
first post-Newtonian approximation of general relativity is considered. Our
approach applies to the motion of an isolated system of arbitrarily
composed and shaped, weakly self-gravitating, rotating, deformable bodies and
uses a framework recently introduced by Damour, Soffel and Xu (DSX). We succeed
in showing that seven of the first integrals of the system (total mass-energy,
total dipole mass moment and total linear momentum) can be broken up into a sum
of contributions which can be entirely expressed in terms of the basic
quantities entering the DSX framework: namely, the relativistic individual
multipole moments of the bodies, the relativistic tidal moments experienced by
each body, and the positions and orientations with respect to the global
coordinate system of the local reference frames attached to each body. On the
other hand, the total angular momentum of the system does not seem to be
expressible in such a form due to the unavoidable presence of irreducible
nonlinear gravitational effects.Comment: 18 pages, Revte
The impact of the Kuiper Belt Objects and of the asteroid ring on future high-precision relativistic Solar System tests
We preliminarily investigate the impact of the Kuiper Belt Objects (KBOs) and
of the asteroid ring on some proposed high-precision tests of Newtonian and
post-Newtonian gravity to be performed in the Solar System by means of
spacecraft in heliocentric \approx 1 AU orbits and accurate orbit determination
of some of the inner planets. It turns out that the Classical KBOSs (CKBOS),
which amount to \approx 70% of the observed population of Trans-Neptunian
bodies, induce a systematic secular error of about 1 m after one year in the
transverse direction T of the orbit of a test particle orbiting at 1 AU from
the Sun. For Mercury the ratios of the secular perihelion precessions induced
by CKBOs to the ones induced by the general relativity and the solar oblateness
J_2 amount to 6 10^-7 and 8 10^-4, respectively. The secular transverse
perturbation induced on a \approx 1 AU orbit by the asteroid ring, which
globally accounts for the action of the minor asteroids whose mass is about 5
10^-10 solar masses, is 10 m yr^-1; the bias on the relativistic and J_2
Mercury perihelion precessions is 6.1 10^-6 and 1 10^-2, respectively. Given
the very ambitious goals of many expensive and complex missions aimed to
testing gravitational theories to unprecedented levels of accuracy, these notes
may suggest further and more accurate investigations of such sources of
potentially insidious systematic bias.Comment: Latex2e, Elsevier macros, 5 pages, no figures, 1 table. To appear in
Planetary Space Science. Small change in table's captio
Primordial black hole evolution in tensor-scalar cosmology
A perturbative analysis shows that black holes do not remember the value of
the scalar field at the time they formed if changes in
tensor-scalar cosmology. Moreover, even when the black hole mass in the
Einstein frame is approximately unaffected by the changing of , in the
Jordan-Fierz frame the mass increases. This mass increase requires a reanalysis
of the evaporation of primordial black holes in tensor-scalar cosmology. It
also implies that there could have been a significant magnification of the
(Jordan-Fierz frame) mass of primordial black holes.Comment: 4 pages, revte
Phasing of gravitational waves from inspiralling eccentric binaries at the third-and-a-half post-Newtonian order
We obtain an efficient description for the dynamics of nonspinning compact
binaries moving in inspiralling eccentric orbits to implement the phasing of
gravitational waves from such binaries at the 3.5 post-Newtonian (PN) order.
Our computation heavily depends on the phasing formalism, presented in [T.
Damour, A. Gopakumar, and B. R. Iyer, Phys. Rev. D \textbf{70}, 064028 (2004)],
and the 3PN accurate generalized quasi-Keplerian parametric solution to the
conservative dynamics of nonspinning compact binaries moving in eccentric
orbits, available in [R.-M. Memmesheimer, A. Gopakumar, and G. Sch\"afer, Phys.
Rev. D \textbf{70}, 104011 (2004)]. The gravitational-wave (GW) polarizations
and with 3.5PN accurate phasing should be useful for the
earth-based GW interferometers, current and advanced, if they plan to search
for gravitational waves from inspiralling eccentric binaries. Our results will
be required to do \emph{astrophysics} with the proposed space-based GW
interferometers like LISA, BBO, and DECIGO.Comment: 22 pages including 2 figures; submitted to PR
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