1,799 research outputs found
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
Gravitational Self Force in a Schwarzschild Background and the Effective One Body Formalism
We discuss various ways in which the computation of conservative
Gravitational Self Force (GSF) effects on a point mass moving in a
Schwarzschild background can inform us about the basic building blocks of the
Effective One-Body (EOB) Hamiltonian. We display the information which can be
extracted from the recently published GSF calculation of the first-GSF-order
shift of the orbital frequency of the last stable circular orbit, and we
combine this information with the one recently obtained by comparing the EOB
formalism to high-accuracy numerical relativity (NR) data on coalescing binary
black holes. The information coming from GSF data helps to break the degeneracy
(among some EOB parameters) which was left after using comparable-mass NR data
to constrain the EOB formalism. We suggest various ways of obtaining more
information from GSF computations: either by studying eccentric orbits, or by
focussing on a special zero-binding zoom-whirl orbit. We show that logarithmic
terms start entering the post-Newtonian expansions of various (EOB and GSF)
functions at the fourth post-Newtonian (4PN) level, and we analytically compute
the first logarithm entering a certain, gauge-invariant "redshift" GSF function
(defined along the sequence of circular orbits).Comment: 44 page
About the Statistical Properties of Cosmological Billiards
We summarize some recent progress in the understanding of the statistical
properties of cosmological billiards.Comment: 10 pages, 5 figures, 2 tables, Proceedings of The second
Galileo-XuGuangqi Meeting, 11-16/07/2010, Ventimiglia, Ital
Post-Newtonian accurate parametric solution to the dynamics of spinning compact binaries in eccentric orbits: The leading order spin-orbit interaction
We derive Keplerian-type parametrization for the solution of post-Newtonian
(PN) accurate conservative dynamics of spinning compact binaries moving in
eccentric orbits. The PN accurate dynamics that we consider consists of the
third post-Newtonian accurate conservative orbital dynamics influenced by the
leading order spin effects, namely the leading order spin-orbit interactions.
The orbital elements of the representation are explicitly given in terms of the
conserved orbital energy, angular momentum and a quantity that characterizes
the leading order spin-orbit interactions in Arnowitt, Deser, and Misner-type
coordinates. Our parametric solution is applicable in the following two
distinct cases: (i) the binary consists of equal mass compact objects, having
two arbitrary spins, and (ii) the binary consists of compact objects of
arbitrary mass, where only one of them is spinning with an arbitrary spin. As
an application of our parametrization, we present gravitational wave
polarizations, whose amplitudes are restricted to the leading quadrupolar
order, suitable to describe gravitational radiation from spinning compact
binaries moving in eccentric orbits. The present parametrization will be
required to construct `ready to use' reference templates for gravitational
waves from spinning compact binaries in inspiralling eccentric orbits. Our
parametric solution for the post-Newtonian accurate conservative dynamics of
spinning compact binaries clearly indicates, for the cases considered, the
absence of chaos in these systems. Finally, we note that our parametrization
provides the first step in deriving a fully second post-Newtonian accurate
`timing formula', that may be useful for the radio observations of relativistic
binary pulsars like J0737-3039.Comment: 18 pages, accepted by Phys. Rev.
Measurability of the tidal polarizability of neutron stars in late-inspiral gravitational-wave signals
The gravitational wave signal from a binary neutron star inspiral contains
information on the nuclear equation of state. This information is contained in
a combination of the tidal polarizability parameters of the two neutron stars
and is clearest in the late inspiral, just before merger. We use the recently
defined tidal extension of the effective one-body formalism to construct a
controlled analytical description of the frequency-domain phasing of neutron
star inspirals up to merger. Exploiting this analytical description we find
that the tidal polarizability parameters of neutron stars can be measured by
the advanced LIGO-Virgo detector network from gravitational wave signals having
a reasonable signal-to-noise ratio of . This measurability result
seems to hold for all the nuclear equations of state leading to a maximum mass
larger than . We also propose a promising new way of extracting
information on the nuclear equation of state from a coherent analysis of an
ensemble of gravitational wave observations of separate binary merger events.Comment: 28 pages, 6 figures. Submitted to Phys. Rev.
Theoretical Aspects of the Equivalence Principle
We review several theoretical aspects of the Equivalence Principle (EP). We
emphasize the unsatisfactory fact that the EP maintains the absolute character
of the coupling constants of physics while General Relativity, and its
generalizations (Kaluza-Klein,..., String Theory), suggest that all absolute
structures should be replaced by dynamical entities. We discuss the
EP-violation phenomenology of dilaton-like models, which is likely to be
dominated by the linear superposition of two effects: a signal proportional to
the nuclear Coulomb energy, related to the variation of the fine-structure
constant, and a signal proportional to the surface nuclear binding energy,
related to the variation of the light quark masses. We recall the various
theoretical arguments (including a recently proposed anthropic argument)
suggesting that the EP be violated at a small, but not unmeasurably small
level. This motivates the need for improved tests of the EP. These tests are
probing new territories in physics that are related to deep, and mysterious,
issues in fundamental physics.Comment: 21 pages, no figures; submitted to a "focus issue" of Classical and
Quantum Gravity on Tests of the Weak Equivalence Principle, organized by
Clive Speake and Clifford Wil
Testing gravity to second post-Newtonian order: a field-theory approach
A new, field-theory-based framework for discussing and interpreting tests of
gravity, notably at the second post-Newtonian (2PN) level, is introduced.
Contrary to previous frameworks which attempted at parametrizing any
conceivable deviation from general relativity, we focus on the best motivated
class of models, in which gravity is mediated by a tensor field together with
one or several scalar fields. The 2PN approximation of these
"tensor-multi-scalar" theories is obtained thanks to a diagrammatic expansion
which allows us to compute the Lagrangian describing the motion of N bodies. In
contrast with previous studies which had to introduce many phenomenological
parameters, we find that the 2PN deviations from general relativity can be
fully described by only two new 2PN parameters, epsilon and zeta, beyond the
usual (Eddington) 1PN parameters beta and gamma. It follows from the basic
tenets of field theory, notably the absence of negative-energy excitations,
that (beta-1), epsilon and zeta (as well as any new parameter entering higher
post-Newtonian orders) must tend to zero with (gamma-1). It is also found that
epsilon and zeta do not enter the 2PN equations of motion of light. Therefore,
light-deflection or time-delay experiments cannot probe any theoretically
motivated 2PN deviation from general relativity, but they can give a clean
access to (gamma-1), which is of greatest significance as it measures the basic
coupling strength of matter to the scalar fields. Because of the importance of
self-gravity effects in neutron stars, binary-pulsar experiments are found to
constitute a unique testing ground for the 2PN structure of gravity. A
simplified analysis of four binary pulsars already leads to significant
constraints: |epsilon| < 7x10^-2, |zeta| < 6x10^-3.Comment: 63 pages, 11 figures.ps.tar.gz.uu, REVTeX 3.
Effective field theory calculation of second post-Newtonian binary dynamics
We use the effective field theory for gravitational bound states, proposed by
Goldberger and Rothstein, to compute the interaction Lagrangian of a binary
system at the second Post-Newtonian order. Throughout the calculation, we use a
metric parametrization based on a temporal Kaluza-Klein decomposition and test
the claim by Kol and Smolkin that this parametrization provides important
calculational advantages. We demonstrate how to use the effective field theory
method efficiently in precision calculations, and we reproduce known results
for the second Post-Newtonian order equations of motion in harmonic gauge in a
straightforward manner.Comment: Replaced with published versio
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