82 research outputs found
Prototype effective-one-body model for nonprecessing spinning inspiral-merger-ringdown waveforms
We first use five non-spinning and two mildly spinning (chi_i \simeq -0.44,
+0.44) numerical-relativity waveforms of black-hole binaries and calibrate an
effective-one-body (EOB) model for non-precessing spinning binaries, notably
its dynamics and the dominant (2,2) gravitational-wave mode. Then, we combine
the above results with recent outcomes of small-mass-ratio simulations produced
by the Teukolsky equation and build a prototype EOB model for detection
purposes, which is capable of generating inspiral-merger-ringdown waveforms for
non-precessing spinning black-hole binaries with any mass ratio and individual
black-hole spins -1 \leq chi_i \lesssim 0.7. We compare the prototype EOB model
to two equal-mass highly spinning numerical-relativity waveforms of black holes
with spins chi_i = -0.95, +0.97, which were not available at the time the EOB
model was calibrated. In the case of Advanced LIGO we find that the mismatch
between prototype-EOB and numerical-relativity waveforms is always smaller than
0.003 for total mass 20-200 M_\odot, the mismatch being computed by maximizing
only over the initial phase and time. To successfully generate merger waveforms
for individual black-hole spins chi_i \gtrsim 0.7, the prototype-EOB model
needs to be improved by (i) better modeling the plunge dynamics and (ii)
including higher-order PN spin terms in the gravitational-wave modes and
radiation-reaction force.Comment: 20 pages, 8 figures. Minor changes to match version accepted for
publication in PR
Relating gravitational wave constraints from primordial nucleosynthesis, pulsar timing, laser interferometers, and the CMB: implications for the early universe
We derive a general master equation relating the gravitational-wave
observables r and Omega_gw(f). Here r is the tensor-to-scalar ratio,
constrained by cosmic-microwave-background (CMB) experiments; and Omega_gw(f)
is the energy spectrum of primordial gravitational-waves, constrained e.g. by
pulsar-timing measurements, laser-interferometer experiments, and Big Bang
Nucleosynthesis (BBN). Differentiating the master equation yields a new
expression for the tilt d(ln Omega_gw(f))/d(ln f). The relationship between r
and Omega_gw(f) depends sensitively on the uncertain physics of the early
universe, and we show that this uncertainty may be encapsulated (in a
model-independent way) by two quantities: w_hat(f) and nt_hat(f), where
nt_hat(f) is a certain logarithmic average over nt(k) (the primordial tensor
spectral index); and w_hat(f) is a certain logarithmic average over w_tilde(a)
(the effective equation-of-state in the early universe, after horizon
re-entry). Here the effective equation-of-state parameter w_tilde(a) is a
combination of the ordinary equation-of-state parameter w(a) and the bulk
viscosity zeta(a). Thus, by comparing constraints on r and Omega_gw(f), one can
obtain (remarkably tight) constraints in the [w_hat(f), nt_hat(f)] plane. In
particular, this is the best way to constrain (or detect) the presence of a
``stiff'' energy component (with w > 1/3) in the early universe, prior to BBN.
Finally, although most of our analysis does not assume inflation, we point out
that if CMB experiments detect a non-zero value for r, then we will immediately
obtain (as a free by-product) a new upper bound w_hat < 0.55 on the
logarithmically averaged effective equation-of-state parameter during the
``primordial dark age'' between the end of inflation and the start of BBN.Comment: v1: 12 + 6 pages (main text + appendices), 7 figures; v2: fonts fixed
in figure
Observational Constraints on Theories with a Blue Spectrum of Tensor Modes
Motivated by the string gas cosmological model, which predicts a blue tilt of
the primordial gravitational wave spectrum, we examine the constraints imposed
by current and planned observations on a blue tilted tensor spectrum. Starting
from an expression for the primordial gravitational wave spectrum normalized
using cosmic microwave background observations, pulsar timing, direct detection
and nucleosynthesis bounds are examined. If we assume a tensor to scalar ratio
on scales of the CMB which equals the current observational upper bound, we
obtain from these current observations constraints on the tensor spectral index
of , , and
respectively.Comment: 12 pages, 1 figure, 2 references added, relationship of this work
with Ref. 20 adde
High-accuracy numerical simulation of black-hole binaries: Computation of the gravitational-wave energy flux and comparisons with post-Newtonian approximants
Expressions for the gravitational wave (GW) energy flux and center-of-mass
energy of a compact binary are integral building blocks of post-Newtonian (PN)
waveforms. In this paper, we compute the GW energy flux and GW frequency
derivative from a highly accurate numerical simulation of an equal-mass,
non-spinning black hole binary. We also estimate the (derivative of the)
center-of-mass energy from the simulation by assuming energy balance. We
compare these quantities with the predictions of various PN approximants
(adiabatic Taylor and Pade models; non-adiabatic effective-one-body (EOB)
models). We find that Pade summation of the energy flux does not accelerate the
convergence of the flux series; nevertheless, the Pade flux is markedly closer
to the numerical result for the whole range of the simulation (about 30 GW
cycles). Taylor and Pade models overestimate the increase in flux and frequency
derivative close to merger, whereas EOB models reproduce more faithfully the
shape of and are closer to the numerical flux, frequency derivative and
derivative of energy. We also compare the GW phase of the numerical simulation
with Pade and EOB models. Matching numerical and untuned 3.5 PN order
waveforms, we find that the phase difference accumulated until
is -0.12 radians for Pade approximants, and 0.50 (0.45) radians for an EOB
approximant with Keplerian (non-Keplerian) flux. We fit free parameters within
the EOB models to minimize the phase difference, and confirm degeneracies among
these parameters. By tuning pseudo 4PN order coefficients in the radial
potential or in the flux, or, if present, the location of the pole in the flux,
we find that the accumulated phase difference can be reduced - if desired - to
much less than the estimated numerical phase error (0.02 radians).Comment: modified non-Keplerian flux improves agreement with NR; updated error
bound of NR-PN comparison; added ref
Inspiral-merger-ringdown multipolar waveforms of nonspinning black-hole binaries using the effective-one-body formalism
We calibrate an effective-one-body (EOB) model to numerical-relativity
simulations of mass ratios 1, 2, 3, 4, and 6, by maximizing phase and amplitude
agreement of the leading (2,2) mode and of the subleading modes (2,1), (3,3),
(4,4) and (5,5). Aligning the calibrated EOB waveforms and the numerical
waveforms at low frequency, the phase difference of the (2,2) mode between
model and numerical simulation remains below 0.1 rad throughout the evolution
for all mass ratios considered. The fractional amplitude difference at peak
amplitude of the (2,2) mode is 2% and grows to 12% during the ringdown. Using
the Advanced LIGO noise curve we study the effectualness and measurement
accuracy of the EOB model, and stress the relevance of modeling the
higher-order modes for parameter estimation. We find that the effectualness,
measured by the mismatch, between the EOB and numerical-relativity
polarizations which include only the (2,2) mode is smaller than 0.2% for
binaries with total mass 20-200 Msun and mass ratios 1, 2, 3, 4, and 6. When
numerical-relativity polarizations contain the strongest seven modes, and
stellar-mass black holes with masses less than 50Msun are considered, the
mismatch for mass ratio 6 (1) can be as high as 5% (0.2%) when only the EOB
(2,2) mode is included, and an upper bound of the mismatch is 0.5% (0.07%) when
all the four subleading EOB modes calibrated in this paper are taken into
account. For binaries with intermediate-mass black holes with masses greater
than 50Msun the mismatches are larger. We also determine for which
signal-to-noise ratios the EOB model developed here can be used to measure
binary parameters with systematic biases smaller than statistical errors due to
detector noise.Comment: 26 pages, 25 figures, published Phys. Rev. D versio
Analytic approximations, perturbation methods, and their applications
The paper summarizes the parallel session B3 {\em Analytic approximations,
perturbation methods, and their applications} of the GR18 conference. The talks
in the session reported notably recent advances in black hole perturbations and
post-Newtonian approximations as applied to sources of gravitational waves.Comment: Summary of the B3 parallel session of the GR18 conferenc
Thermal Inflation and the Gravitational Wave Background
We consider the impact of thermal inflation -- a short, secondary period of
inflation that can arise in supersymmetric scenarios -- on the stochastic
gravitational wave background. We show that while the primordial inflationary
gravitational wave background is essentially unchanged at CMB scales, it is
massively diluted at solar system scales and would be unobservable by a BBO
style experiment. Conversely, bubble collisions at the end of thermal inflation
can generate a new stochastic background. We calculate the likely properties of
the bubbles created during this phase transition, and show that the expected
amplitude and frequency of this signal would fall within the BBO range.Comment: 21 pages, 4 figures; accepted for JCAP; a reference added; table
reformatte
Comparison of high-accuracy numerical simulations of black-hole binaries with stationary phase post-Newtonian template waveforms for Initial and Advanced LIGO
We study the effectiveness of stationary-phase approximated post-Newtonian
waveforms currently used by ground-based gravitational-wave detectors to search
for the coalescence of binary black holes by comparing them to an accurate
waveform obtained from numerical simulation of an equal-mass non-spinning
binary black hole inspiral, merger and ringdown. We perform this study for the
Initial- and Advanced-LIGO detectors. We find that overlaps between the
templates and signal can be improved by integrating the match filter to higher
frequencies than used currently. We propose simple analytic frequency cutoffs
for both Initial and Advanced LIGO, which achieve nearly optimal matches, and
can easily be extended to unequal-mass, spinning systems. We also find that
templates that include terms in the phase evolution up to 3.5 pN order are
nearly always better, and rarely significantly worse, than 2.0 pN templates
currently in use. For Initial LIGO we recommend a strategy using templates that
include a recently introduced pseudo-4.0 pN term in the low-mass (M \leq 35
\MSun) region, and 3.5 pN templates allowing unphysical values of the
symmetric reduced mass above this. This strategy always achieves
overlaps within 0.3% of the optimum, for the data used here. For Advanced LIGO
we recommend a strategy using 3.5 pN templates up to M=12 \MSun, 2.0 pN
templates up to M=21 \MSun, pseudo-4.0 pN templates up to 65 \MSun, and 3.5
pN templates with unphysical for higher masses. This strategy always
achieves overlaps within 0.7% of the optimum for Advanced LIGO.Comment: 20 pages, 11 figures. Presented at NRDA 200
Gravitational waveforms from spectral Einstein code simulations: Neutron star-neutron star and low-mass black hole-neutron star binaries
Gravitational waveforms from numerical simulations are a critical tool to test and analytically calibrate the waveform models used to study the properties of merging compact objects. In this paper, we present a series of high-accuracy waveforms produced with the spectral Einstein code (SpEC) for systems involving at least one neutron star. We provide for the first time waveforms with subradian accuracy over more than twenty cycles for low-mass black hole-neutron star binaries, including binaries with nonspinning objects, and binaries with rapidly spinning neutron stars that maximize the impact on the gravitational wave signal of the near-resonant growth of the fundamental excitation mode of the neutron star (f-mode). We also provide for the first time with SpEC a high-accuracy neutron star-neutron star waveform. These waveforms are made publicly available as part of the SxS catalogue. We compare our results to analytical waveform models currently implemented in data analysis pipelines. For most simulations, the models lie outside of the predicted numerical errors in the last few orbits before merger, but do not show systematic deviations from the numerical results: comparing different models appears to provide reasonable estimates of the modeling errors. The sole exception is the equal-mass simulation using a rapidly counterrotating neutron star to maximize the impact of the excitation of the f-mode, for which all models perform poorly. This is however expected, as even the single model that takes f-mode excitation into account ignores the significant impact of the neutron star spin on the f-mode excitation frequency
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