49 research outputs found
Flux-balance laws in scalar self-force theory
The motion of a radiating point particle can be represented by a series of
geodesics whose "constants" of motion evolve slowly with time. The evolution of
these constants of motion can be determined directly from the self-force
equations of motion. In the presence of spacetime symmetries, the situation
simplifies: there exist not only constants of motion conjugate to these
symmetries, but also conserved currents whose fluxes can be used to determine
their evolution. Such a relationship between point-particle motion and fluxes
of conserved currents is a flux-balance law. However, there exist constants of
motion that are not related to spacetime symmetries, the most notable example
of which is the Carter constant in the Kerr spacetime. In this paper, we first
present a new approach to flux-balance laws for spacetime symmetries, using the
techniques of symplectic currents and symmetry operators, which can also
generate more general conserved currents. We then derive flux-balance laws for
all constants of motion in the Kerr spacetime, using the fact that the
background, geodesic motion is integrable. For simplicity, we restrict
derivations in this paper to the scalar self-force problem. While generalizing
the discussion in this paper to the gravitational case will be straightforward,
there will be additional complications in turning these results into a
practical flux-balance law in this case.Comment: 15+3 pages, 1 figure; v2: corrected typos and added appendix and
figure, "matches" published versio
Gravity waves and non-Gaussian features from particle production in a sector gravitationally coupled to the inflaton
We study the possibility that particle production during inflation could
source observable gravity waves on scales relevant for Cosmic Microwave
Background experiments. A crucial constraint on such scenarios arises because
particle production can also source inflaton perturbations, and might ruin the
usual predictions for a nearly scale invariant spectrum of nearly Gaussian
curvature fluctuations. To minimize this effect, we consider two models of
particle production in a sector that is only gravitationally coupled to the
inflaton. For a single instantaneous burst of massive particle production, we
find that localized features in the scalar spectrum and bispectrum might be
observable, but gravitational wave signatures are unlikely to be detectable
(due to the suppressed quadrupole moment of non-relativistic quanta) without
invoking some additional effects. We also consider a model with a rolling
pseudoscalar that leads to a continuous production of relativistic gauge field
fluctuations during inflation. Here we find that gravitational waves from
particle production can actually exceed the usual inflationary vacuum
fluctuations in a regime where non-Gaussianity is consistent with observational
limits. In this model observable B-mode polarization can be obtained for any
choice of inflaton potential, and the amplitude of the signal is not
necessarily correlated with the scale of inflation
Numerical relativity simulation of GW150914 beyond general relativity
We produce the first astrophysically-relevant numerical binary black hole
gravitational waveform in a higher-curvature theory of gravity beyond general
relativity. We simulate a system with parameters consistent with GW150914, the
first LIGO detection, in order-reduced dynamical Chern-Simons gravity, a theory
with motivations in string theory and loop quantum gravity. We present results
for the leading-order corrections to the merger and ringdown waveforms, as well
as the ringdown quasi-normal mode spectrum. We estimate that such corrections
may be discriminated in detections with signal to noise ratio , with the precise value depending on the dimension of the GR waveform
family used in data analysis.Comment: 7 pages + appendices, 8 figures, Updated to match Phys. D. Rev
articl
Improved Cauchy-characteristic evolution system for high-precision numerical relativity waveforms
We present several improvements to the Cauchy-characteristic evolution procedure that generates high-fidelity gravitational waveforms at I+ from numerical relativity simulations. Cauchy-characteristic evolution combines an interior solution of the Einstein field equations based on Cauchy slices with an exterior solution based on null slices that extend to I+. The foundation of our improved algorithm is a comprehensive method of handling the gauge transformations between the arbitrarily specified coordinates of the interior Cauchy evolution and the unique (up to Bondi-Metzner-Sachs group transformations) Bondi-Sachs coordinate system of the exterior characteristic evolution. We present a reformulated set of characteristic evolution equations better adapted to numerical implementation. In addition, we develop a method to ensure that the angular coordinates used in the volume during the characteristic evolution are asymptotically inertial. This provides a direct route to an expanded set of waveform outputs and is guaranteed to avoid pure-gauge logarithmic dependence that has caused trouble for previous spectral implementations of the characteristic evolution equations. We construct a set of Weyl scalars compatible with the Bondi-like coordinate systems used in characteristic evolution and determine simple, easily implemented forms for the asymptotic Weyl scalars in our suggested set of coordinates
Spectral Cauchy-characteristic extraction of the gravitational wave news function
We present an improved spectral algorithm for Cauchy-characteristic
extraction and characteristic evolution of gravitational waves in numerical
relativity. The new algorithms improve spectral convergence both at the poles
of the spherical-polar grid and at future null infinity, as well as increase
the temporal resolution of the code. The key to the success of these algorithms
is a new set of high-accuracy tests, which we present here. We demonstrate the
accuracy of the code and compare with the existing PittNull implementation.Comment: 26 pages, 8 figures, published versio
Spectral Cauchy-characteristic extraction of the gravitational wave news function
We present an improved spectral algorithm for Cauchy-characteristic extraction and characteristic evolution of gravitational waves in numerical relativity. The new algorithms improve spectral convergence both at the poles of the spherical-polar grid and at future null infinity, as well as increase the temporal resolution of the code. The key to the success of these algorithms is a new set of high-accuracy tests, which we present here. We demonstrate the accuracy of the code and compare with the existing pittnull implementation
Numerical relativity simulation of GW150914 beyond general relativity
We produce the first astrophysically relevant numerical binary black hole gravitational waveform in a higher-curvature theory of gravity beyond general relativity. We simulate a system with parameters consistent with GW150914, the first LIGO detection, in order-reduced dynamical Chern-Simons gravity, a theory with motivations in string theory and loop quantum gravity. We present results for the leading-order corrections to the merger and ringdown waveforms, as well as the ringdown quasinormal mode spectrum. We estimate that such corrections may be discriminated in detections with signal to noise ratio âł180â240, with the precise value depending on the dimension of the GR waveform family used in data analysis
Computation of displacement and spin gravitational memory in numerical relativity
We present the first numerical relativity waveforms for binary black hole mergers produced using spectral methods that show both the displacement and the spin memory effects. Explicitly, we use the SXS (Simulating eXtreme Spacetimes) Collaborationâs SpEC code to run a Cauchy evolution of a binary black hole merger and then extract the gravitational wave strain using SpECTREâs version of a Cauchy-characteristic extraction. We find that we can accurately resolve the strainâs traditional m=0 memory modes and some of the mâ 0 oscillatory memory modes that have previously only been theorized. We also perform a separate calculation of the memory using equations for the Bondi-Metzner-Sachs charges as well as the energy and angular momentum fluxes at asymptotic infinity. Our new calculation uses only the gravitational wave strain and two of the Weyl scalars at infinity. Also, this computation shows that the memory modes can be understood as a combination of a memory signal throughout the binaryâs inspiral and merger phases, and a quasinormal mode signal near the ringdown phase. Additionally, we find that the magnetic memory, up to numerical error, is indeed zero as previously conjectured. Last, we find that signal-to-noise ratios of memory for LIGO, the Einstein Telescope, and the Laser Interferometer Space Antenna with these new waveforms and new memory calculation are larger than previous expectations based on post-Newtonian or minimal waveform models