499 research outputs found
A new PPN parameter to test Chern-Simons gravity
We study Chern-Simons (CS) gravity in the parameterized post-Newtonian (PPN)
framework through a weak-field solution of the modified field equations. We
find that CS gravity possesses the same PPN parameters as general relativity,
except for the inclusion of a new term, proportional to the CS coupling and the
curl of the PPN vector potential. This new term leads to a modification of
frame dragging and gyroscopic precession and we provide an estimate of its
size. This correction might be used in experiments, such as Gravity Probe B, to
bound CS gravity and test string theory.Comment: 4 pages, replaced with version accepted for publication in Phys. Rev.
Letters (December, 2007
Extreme Mass-Ratio Inspirals in the Effective-One-Body Approach: Quasi-Circular, Equatorial Orbits around a Spinning Black Hole
We construct effective-one-body waveform models suitable for data analysis
with LISA for extreme-mass ratio inspirals in quasi-circular, equatorial orbits
about a spinning supermassive black hole. The accuracy of our model is
established through comparisons against frequency-domain, Teukolsky-based
waveforms in the radiative approximation. The calibration of eight high-order
post-Newtonian parameters in the energy flux suffices to obtain a phase and
fractional amplitude agreement of better than 1 radian and 1 % respectively
over a period between 2 and 6 months depending on the system considered. This
agreement translates into matches higher than 97 % over a period between 4 and
9 months, depending on the system. Better agreements can be obtained if a
larger number of calibration parameters are included. Higher-order mass ratio
terms in the effective-one-body Hamiltonian and radiation-reaction introduce
phase corrections of at most 30 radians in a one year evolution. These
corrections are usually one order of magnitude larger than those introduced by
the spin of the small object in a one year evolution. These results suggest
that the effective-one-body approach for extreme mass ratio inspirals is a good
compromise between accuracy and computational price for LISA data analysis
purposes.Comment: 21 pages, 8 figures, submitted to Phys. Rev.
Gravitational Waves from Quasi-Circular Black Hole Binaries in Dynamical Chern-Simons Gravity
Dynamical Chern-Simons gravity cannot be strongly constrained with current
experiments because it reduces to General Relativity in the weak-field limit.
This theory, however, introduces modifications in the non-linear, dynamical
regime, and thus, it could be greatly constrained with gravitational waves from
the late inspiral of black hole binaries. We complete the first self-consistent
calculation of such gravitational waves in this theory. For favorable
spin-orientations, advanced ground-based detectors may improve existing
solar-system constraints by 6 orders of magnitude.Comment: 6 pages, 1 figure; errors corrected in Eqs. (8) and (9
Cross section, final spin and zoom-whirl behavior in high-energy black hole collisions
We study the collision of two highly boosted equal mass, nonrotating black
holes with generic impact parameter. We find such systems to exhibit zoom-whirl
behavior when fine tuning the impact parameter. Near the threshold of immediate
merger the remnant black hole Kerr parameter can be near maximal (a/M about
0.95) and the radiated energy can be as large as 35% of the center-of-mass
energy.Comment: Rearranged results section; accepted for publication in Phys. Rev.
Let
Model-Independent Test of General Relativity: An Extended post-Einsteinian Framework with Complete Polarization Content
We develop a model-independent test of General Relativity that allows for the
constraint of the gravitational wave (GW) polarization content with GW
detections of binary compact object inspirals. We first consider three modified
gravity theories (Brans-Dicke theory, Rosen's theory and Lightman-Lee theory)
and calculate the response function of ground-based detectors to gravitational
waves in the inspiral phase. This allows us to see how additional polarizations
predicted in these theories modify the General Relativistic prediction of the
response function. We then consider general power-law modifications to the
Hamiltonian and radiation-reaction force and study how these modify the
time-domain and Fourier response function when all polarizations are present.
From these general arguments and specific modified gravity examples, we infer
an improved parameterized post-Einsteinian template family with complete
polarization content. This family enhances General Relativity templates through
the inclusion of new theory parameters, reducing to the former when these
parameters acquire certain values, and recovering modified gravity predictions
for other values, including all polarizations. We conclude by discussing
detection strategies to constrain these new, polarization theory parameters by
constructing certain null channels through the combination of output from
multiple detectors.Comment: 20 pages, 1 figure, added erratum correcting some intermediate
equation
Binary black hole initial data from matched asymptotic expansions
We present an approximate metric for a binary black hole spacetime to
construct initial data for numerical relativity. This metric is obtained by
asymptotically matching a post-Newtonian metric for a binary system to a
perturbed Schwarzschild metric for each hole. In the inner zone near each hole,
the metric is given by the Schwarzschild solution plus a quadrupolar
perturbation corresponding to an external tidal gravitational field. In the
near zone, well outside each black hole but less than a reduced wavelength from
the center of mass of the binary, the metric is given by a post-Newtonian
expansion including the lowest-order deviations from flat spacetime. When the
near zone overlaps each inner zone in a buffer zone, the post-Newtonian and
perturbed Schwarzschild metrics can be asymptotically matched to each other. By
demanding matching (over a 4-volume in the buffer zone) rather than patching
(choosing a particular 2-surface in the buffer zone), we guarantee that the
errors are small in all zones. The resulting piecewise metric is made formally
with smooth transition functions so as to obtain the finite
extrinsic curvature of a 3-slice. In addition to the metric and extrinsic
curvature, we present explicit results for the lapse and the shift, which can
be used as initial data for numerical simulations. This initial data is not
accurate all the way to the asymptotically flat ends inside each hole, and
therefore must be used with evolution codes which employ black hole excision
rather than puncture methods. This paper lays the foundations of a method that
can be sraightforwardly iterated to obtain initial data to higher perturbative
order.Comment: 24 pages, 15 figures. Replaced with published version. Major editing
of text, no major change to the physic
Generic bounds on dipolar gravitational radiation from inspiralling compact binaries
Various alternative theories of gravity predict dipolar gravitational
radiation in addition to quadrupolar radiation. We show that gravitational wave
(GW) observations of inspiralling compact binaries can put interesting
constraints on the strengths of the dipole modes of GW polarizations. We put
forward a physically motivated gravitational waveform for dipole modes, in the
Fourier domain, in terms of two parameters: one which captures the relative
amplitude of the dipole mode with respect to the quadrupole mode () and
the other a dipole term in the phase (). We then use this two parameter
representation to discuss typical bounds on their values using GW measurements.
We obtain the expected bounds on the amplitude parameter and the phase
parameter for Advanced LIGO (AdvLIGO) and Einstein Telescope (ET) noise
power spectral densities using Fisher information matrix. AdvLIGO and ET may at
best bound to an accuracy of and and
to an accuracy of and respectively.Comment: Matches with the published versio
Slowly Rotating Black Holes in Dynamical Chern-Simons Gravity: Deformation Quadratic in the Spin
We derive a stationary and axisymmetric black hole solution to quadratic
order in the spin angular momentum. The previously found, linear-in-spin terms
modify the odd-parity sector of the metric, while the new corrections appear in
the even-parity sector. These corrections modify the quadrupole moment, as well
as the (coordinate-dependent) location of the event horizon and the ergoregion.
Although the linear-in-spin metric is of Petrov type D, the quadratic order
terms render it of type I. The metric does not possess a second-order Killing
tensor or a Carter-like constant. The new metric does not possess closed
timelike curves or spacetime regions that violate causality outside of the
event horizon. The new, even-parity modifications to the Kerr metric decay less
rapidly at spatial infinity than the leading-order in spin, odd-parity ones,
and thus, the former are more important when considering black holes that are
rotating moderately fast. We calculate the modifications to the Hamiltonian,
binding energy and Kepler's third law. These modifications are crucial for the
construction of gravitational wave templates for black hole binaries, which
will enter at second post-Newtonian order, just like dissipative modifications
found previously.Comment: 21 pages, 2 figures; Typos correcte
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