1,711 research outputs found
Measuring stochastic gravitational-wave energy beyond general relativity
Gravity theories beyond general relativity (GR) can change the properties of
gravitational waves: their polarizations, dispersion, speed, and, importantly,
energy content are all heavily theory- dependent. All these corrections can
potentially be probed by measuring the stochastic gravitational- wave
background. However, most existing treatments of this background beyond GR
overlook modifications to the energy carried by gravitational waves, or rely on
GR assumptions that are invalid in other theories. This may lead to
mistranslation between the observable cross-correlation of detector outputs and
gravitational-wave energy density, and thus to errors when deriving
observational constraints on theories. In this article, we lay out a generic
formalism for stochastic gravitational- wave searches, applicable to a large
family of theories beyond GR. We explicitly state the (often tacit) assumptions
that go into these searches, evaluating their generic applicability, or lack
thereof. Examples of problematic assumptions are: statistical independence of
linear polarization amplitudes; which polarizations satisfy equipartition; and
which polarizations have well-defined phase velocities. We also show how to
correctly infer the value of the stochastic energy density in the context of
any given theory. We demonstrate with specific theories in which some of the
traditional assumptions break down: Chern-Simons gravity, scalar-tensor theory,
and Fierz-Pauli massive gravity. In each theory, we show how to properly
include the beyond-GR corrections, and how to interpret observational results.Comment: 18 pages (plus appendices), 1 figur
Black-hole kicks from numerical-relativity surrogate models
Binary black holes radiate linear momentum in gravitational waves as they
merge. Recoils imparted to the black-hole remnant can reach thousands of km/s,
thus ejecting black holes from their host galaxies. We exploit recent advances
in gravitational waveform modeling to quickly and reliably extract recoils
imparted to generic, precessing, black hole binaries. Our procedure uses a
numerical-relativity surrogate model to obtain the gravitational waveform given
a set of binary parameters, then from this waveform we directly integrate the
gravitational-wave linear momentum flux. This entirely bypasses the need of
fitting formulae which are typically used to model black-hole recoils in
astrophysical contexts. We provide a thorough exploration of the black-hole
kick phenomenology in the parameter space, summarizing and extending previous
numerical results on the topic. Our extraction procedure is made publicly
available as a module for the Python programming language named SURRKICK. Kick
evaluations take ~0.1s on a standard off-the-shelf machine, thus making our
code ideal to be ported to large-scale astrophysical studies.Comment: More: https://davidegerosa.com/surrkick - Source:
https://github.com/dgerosa/surrkick - pypi:
https://pypi.python.org/pypi/surrkick - Published in PR
Extremal Black Holes in Dynamical Chern-Simons Gravity
Rapidly rotating black hole solutions in theories beyond general relativity
play a key role in experimental gravity, as they allow us to compute
observables in extreme spacetimes that deviate from the predictions of general
relativity. Such solutions are often difficult to find in
beyond-general-relativity theories due to the inclusion of additional fields
that couple to the metric non-linearly and non-minimally. In this paper, we
consider rotating black hole solutions in one such theory, dynamical
Chern-Simons gravity, where the Einstein-Hilbert action is modified by the
introduction of a dynamical scalar field that couples to the metric through the
Pontryagin density. We treat dynamical Chern-Simons gravity as an effective
field theory and work in the decoupling limit, where corrections are treated as
small perturbations from general relativity. We perturb about the
maximally-rotating Kerr solution, the so-called extremal limit, and develop
mathematical insight into the analysis techniques needed to construct solutions
for generic spin. First we find closed-form, analytic expressions for the
extremal scalar field, and then determine the trace of the metric perturbation,
giving both in terms of Legendre decompositions. Retaining only the first three
and four modes in the Legendre representation of the scalar field and the
trace, respectively, suffices to ensure a fidelity of over 99% relative to full
numerical solutions. The leading-order mode in the Legendre expansion of the
trace of the metric perturbation contains a logarithmic divergence at the
extremal Kerr horizon, which is likely to be unimportant as it occurs inside
the perturbed dynamical Chern-Simons horizon. The techniques employed here
should enable the construction of analytic, closed-form expressions for the
scalar field and metric perturbations on a background with arbitrary rotation.Comment: 25+9 pages (single column), 10 figures, 1 table; matches published
versio
Modeling the Dispersion and Polarization Content of Gravitational Waves for Tests of General Relativity
We propose a generic, phenomenological approach to modifying the dispersion
of gravitational waves, independent of corrections to the generation mechanism.
This model-independent approach encapsulates all previously proposed
parametrizations, including Lorentz violation in the Standard-Model Extension,
and provides a roadmap for additional theories. Furthermore, we present a
general approach to include modulations to the gravitational-wave polarization
content. The framework developed here can be implemented in existing data
analysis pipelines for future gravitational-wave observation runs.Comment: 4 pages, Presented at the Seventh Meeting on CPT and Lorentz
Symmetry, Bloomington, Indiana, June 20-24, 201
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