513 research outputs found
Fast and accurate prediction of numerical relativity waveforms from binary black hole coalescences using surrogate models
Simulating a binary black hole (BBH) coalescence by solving Einstein's
equations is computationally expensive, requiring days to months of
supercomputing time. Using reduced order modeling techniques, we construct an
accurate surrogate model, which is evaluated in a millisecond to a second, for
numerical relativity (NR) waveforms from non-spinning BBH coalescences with
mass ratios in and durations corresponding to about orbits
before merger. We assess the model's uncertainty and show that our modeling
strategy predicts NR waveforms {\em not} used for the surrogate's training with
errors nearly as small as the numerical error of the NR code. Our model
includes all spherical-harmonic waveform modes resolved by
the NR code up to We compare our surrogate model to Effective One
Body waveforms from - for advanced LIGO detectors and find
that the surrogate is always more faithful (by at least an order of magnitude
in most cases).Comment: Updated to published version, which includes a section comparing the
surrogate and effective-one-body models. The surrogate is publicly available
for download at http://www.black-holes.org/surrogates/ . 6 pages, 6 figure
A Surrogate Model of Gravitational Waveforms from Numerical Relativity Simulations of Precessing Binary Black Hole Mergers
We present the first surrogate model for gravitational waveforms from the
coalescence of precessing binary black holes. We call this surrogate model
NRSur4d2s. Our methodology significantly extends recently introduced
reduced-order and surrogate modeling techniques, and is capable of directly
modeling numerical relativity waveforms without introducing phenomenological
assumptions or approximations to general relativity. Motivated by GW150914,
LIGO's first detection of gravitational waves from merging black holes, the
model is built from a set of numerical relativity (NR) simulations with
mass ratios , dimensionless spin magnitudes up to , and the
restriction that the initial spin of the smaller black hole lies along the axis
of orbital angular momentum. It produces waveforms which begin
gravitational wave cycles before merger and continue through ringdown, and
which contain the effects of precession as well as all
spin-weighted spherical-harmonic modes. We perform cross-validation studies to
compare the model to NR waveforms \emph{not} used to build the model, and find
a better agreement within the parameter range of the model than other,
state-of-the-art precessing waveform models, with typical mismatches of
. We also construct a frequency domain surrogate model (called
NRSur4d2s_FDROM) which can be evaluated in and is suitable
for performing parameter estimation studies on gravitational wave detections
similar to GW150914.Comment: 34 pages, 26 figure
A Numerical Relativity Waveform Surrogate Model for Generically Precessing Binary Black Hole Mergers
A generic, non-eccentric binary black hole (BBH) system emits gravitational
waves (GWs) that are completely described by 7 intrinsic parameters: the black
hole spin vectors and the ratio of their masses. Simulating a BBH coalescence
by solving Einstein's equations numerically is computationally expensive,
requiring days to months of computing resources for a single set of parameter
values. Since theoretical predictions of the GWs are often needed for many
different source parameters, a fast and accurate model is essential. We present
the first surrogate model for GWs from the coalescence of BBHs including all
dimensions of the intrinsic non-eccentric parameter space. The surrogate
model, which we call NRSur7dq2, is built from the results of numerical
relativity simulations. NRSur7dq2 covers spin magnitudes up to and mass
ratios up to , includes all modes, begins about orbits
before merger, and can be evaluated in . We find the
largest NRSur7dq2 errors to be comparable to the largest errors in the
numerical relativity simulations, and more than an order of magnitude smaller
than the errors of other waveform models. Our model, and more broadly the
methods developed here, will enable studies that would otherwise require
millions of numerical relativity waveforms, such as parameter inference and
tests of general relativity with GW observations.Comment: 10 pages, 5 figures; Added report numbe
Finite size corrections to the radiation reaction force in classical electrodynamics
We introduce an effective field theory approach that describes the motion of
finite size objects under the influence of electromagnetic fields. We prove
that leading order effects due to the finite radius of a spherically
symmetric charge is order rather than order in any physical model, as
widely claimed in the literature. This scaling arises as a consequence of
Poincar\'e and gauge symmetries, which can be shown to exclude linear
corrections. We use the formalism to calculate the leading order finite size
correction to the Abraham-Lorentz-Dirac force.Comment: 4 pages, 2 figure
Differential Effects of MitoVitE, α-Tocopherol and Trolox on Oxidative Stress, Mitochondrial Function and Inflammatory Signalling Pathways in Endothelial Cells Cultured under Conditions Mimicking Sepsis
Funding: This research was funded by The British Journal of Anaesthesia/Royal College of Anaesthetists (PhD studentship to Beverley Minter). Acknowledgments: We are very grateful to Professor M.P. Murphy, MRC Mitochondrial Biology Unit, Wellcome Trust/MRC Building, Hills Road, Cambridge, UK for the generous gift of MitoVitE used in all the experiments, without which this work would not have been possible.Peer reviewedPublisher PD
A nonlinear scalar model of extreme mass ratio inspirals in effective field theory I. Self force through third order
The motion of a small compact object in a background spacetime is
investigated in the context of a model nonlinear scalar field theory. This
model is constructed to have a perturbative structure analogous to the General
Relativistic description of extreme mass ratio inspirals (EMRIs). We apply the
effective field theory approach to this model and calculate the finite part of
the self force on the small compact object through third order in the ratio of
the size of the compact object to the curvature scale of the background (e.g.,
black hole) spacetime. We use well-known renormalization methods and
demonstrate the consistency of the formalism in rendering the self force finite
at higher orders within a point particle prescription for the small compact
object. This nonlinear scalar model should be useful for studying various
aspects of higher-order self force effects in EMRIs but within a comparatively
simpler context than the full gravitational case. These aspects include
developing practical schemes for higher order self force numerical
computations, quantifying the effects of transient resonances on EMRI waveforms
and accurately modeling the small compact object's motion for precise
determinations of the parameters of detected EMRI sources.Comment: 30 pages, 8 figure
Self-force on extreme mass ratio inspirals via curved spacetime effective field theory
In this series we construct an effective field theory (EFT) in curved
spacetime to study gravitational radiation and backreaction effects. We begin
in this paper with a derivation of the self-force on a compact object moving in
the background spacetime of a supermassive black hole. The EFT approach
utilizes the disparity between two length scales, which in this problem are the
size of the compact object and the radius of curvature of the background
spacetime, to treat the orbital dynamics of the compact object, described as an
effective point particle, separately from its tidal deformations. Ultraviolet
divergences are regularized using Hadamard's {\it partie finie} to isolate the
non-local finite part from the quasi-local divergent part. The latter is
constructed from a momentum space representation for the graviton retarded
propagator and is evaluated using dimensional regularization in which only
logarithmic divergences are relevant for renormalizing the parameters of the
theory. As a first important application of this framework we explicitly derive
the first order self-force given by Mino, Sasaki, Tanaka, Quinn and Wald. Going
beyond the point particle approximation, to account for the finite size of the
object, we demonstrate that for extreme mass ratio inspirals the motion of a
compact object is affected by tidally induced moments at , in
the form of an Effacement Principle. The relatively large radius-to-mass ratio
of a white dwarf star allows for these effects to be enhanced until the white
dwarf becomes tidally disrupted, a potentially process, or
plunges into the supermassive black hole. This work provides a new foundation
for further exploration of higher order self force corrections, gravitational
radiation and spinning compact objects.Comment: 22 pages, 5 figures; references added, revised Appendices B & C,
corrected typos, revisions throughout for clarification particularly in
Section IV.B; submitted to PR
Quantum Relativity of Subsystems
One of the most basic notions in physics is the partitioning of a system into
subsystems, and the study of correlations among its parts. In this work, we
explore these notions in the context of quantum reference frame (QRF)
covariance, in which this partitioning is subject to a symmetry constraint. We
demonstrate that different reference frame perspectives induce different sets
of subsystem observable algebras, which leads to a gauge-invariant,
frame-dependent notion of subsystems and entanglement. We further demonstrate
that subalgebras which commute before imposing the symmetry constraint can
translate into non-commuting algebras in a given QRF perspective after symmetry
imposition. Such a QRF perspective does not inherit the distinction between
subsystems in terms of the corresponding tensor factorizability of the
kinematical Hilbert space and observable algebra. Since the condition for this
to occur is contingent on the choice of QRF, the notion of subsystem locality
is frame-dependent.Comment: 8+9 pages, 1 figur
Radiation reaction and gravitational waves in the effective field theory approach
We compute the contribution to the Lagrangian from the leading order (2.5
post-Newtonian) radiation reaction and the quadrupolar gravitational waves
emitted from a binary system using the effective field theory (EFT) approach of
Goldberger and Rothstein. We use an initial value formulation of the underlying
(quantum) framework to implement retarded boundary conditions and describe
these real-time dissipative processes. We also demonstrate why the usual
scattering formalism of quantum field theory inadequately accounts for these.
The methods discussed here should be useful for deriving real-time quantities
(including radiation reaction forces and gravitational wave emission) and
hereditary terms in the post-Newtonian approximation (including memory, tail
and other causal, history-dependent integrals) within the EFT approach. We also
provide a consistent formulation of the radiation sector in the equivalent
effective field theory approach of Kol and Smolkin.Comment: 23 pages, 8 figure
Bench-to-bedside review : targeting antioxidants to mitochondria in sepsis
Peer reviewedPublisher PD
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