The detection of an electromagnetic counterpart (GRB 170817A) to the gravitational-wave signal (GW170817) from merger two neutron stars opens a completely new arena for testing theories gravity. We show that this measurement allows us place stringent constraints on general scalar-tensor and vector-tensor theories, while allowing independent bound graviton mass in bimetric These severely reduce viable range cosmological models have been proposed as alternatives relativistic cosmology.Received...

The gravitational wave strain emitted by a perturbed black hole (BH) ringing down is typically modeled analytically using first-order BH perturbation theory. In this Letter, we show that second-order effects are necessary for modeling ringdowns from merger simulations. Focusing on the strain's (ℓ,m)=(4,4) angular harmonic, presence of quadratic effect across range binary mass ratios agrees with theoretical expectations. We find (4,4) mode's amplitude exhibits scaling fundamental (2,2)...

In the analysis of a binary black hole coalescence, it is necessary to include gravitational self-interactions in order describe transition wave signal from merger ringdown stage. this paper we study phenomenology generation and propagation nonlinearities Schwarzschild hole, using second-order perturbation theory. Following earlier work, show that Green's function its causal structure determines how both first-order perturbations are generated, hence highlight these solutions share some...

Assessing the probability that two or more gravitational waves (GWs) are lensed images of same source requires an understanding image properties, including their relative phase shifts in strong lensing (SL). For non-precessing, circular binaries dominated by quadrupole radiation these degenerate with either a shift coalescence detector and inclination dependent orientation angle. This degeneracy is broken presence higher harmonic modes $|m|\ne 2$ former $|m| \ne l$ latter. Precession...

We present a comprehensive analysis of classical scalar, vector and tensor cosmological perturbations in ghost-free massive bigravity. In particular, we find the full evolution equations analytical solutions wide range regimes. show that there are viable backgrounds but, as has been found literature, these models generally have exponential instabilities linear perturbation theory. However, it is possible to stable scalar for very particular choice parameters. For this subclass growing...

We consider the effect of a time-varying Planck mass on propagation gravitational waves (GWs). A running arises naturally in several modified-gravity theories, and here we focus those that carry an additional dark energy field responsible for late-time accelerated expansion Universe, yet---like general relativity (GR)---propagate only two GW polarizations, both traveling at speed light. Because affects amplitude GWs therefore inferred distance to source, standard siren measurements ${H}_{0}$...

We present a method for parametrizing linear cosmological perturbations of theories gravity, around homogeneous and isotropic backgrounds. The is sufficiently general systematic that it can be applied to with any degrees freedom (DoFs) arbitrary gauge symmetries. In this paper, we focus on scalar-tensor vector-tensor theories, invariant under coordinate transformations. the case use our framework recover simple parametrizations linearized Horndeski ``Beyond Horndeski'' also find...

Abstract We study the cosmological propagation of gravitational waves (GWs) beyond general relativity (GR) across homogeneous and isotropic backgrounds. consider scenarios in which GWs interact with an additional tensor field use a parametrized phenomenological approach that generically describes their coupled equations motion. analyze four distinct classes derivative non-derivative interactions: mass, friction, velocity, chiral. apply WKB formalism to account for evolution obtain analytical...

Gravitational parity violation arises in a variety of theories beyond general relativity. waves such have their propagation altered, leading to birefringence effects both the amplitude and speed wave. In this work, we introduce generalized, theory-motivated parametrization scheme study gravitational wave propagation. This maps parity-violating gravity straightforward way. We find that velocity scale with an effective distance measure depends on how dispersion relation is modified....

Extensions to general relativity allow the polarization of gravitational waves (GW) from astrophysical sources suffer amplitude and velocity birefringence, which respectively induce changes in ellipticity orientation tensor. We introduce a multimessenger approach test this behavior GWs during their cosmological propagation using binary sources, for initial is determined by inclination angles orbital angular momentum vector with respect line sight. In particular, we use spatially resolved...

We use the covariant formulation proposed by Tattersall, Lagos, and Ferreira [Phys. Rev. D 96, 064011 (2017)] to analyze structure of linear perturbations about a spherically symmetric background in different families gravity theories, hence study how quasinormal modes perturbed black holes may be affected modifications general relativity. restrict ourselves single-tensor, scalar-tensor vector-tensor diffeomorphism-invariant models Schwarzschild hole background. show explicitly full form...

The recent detection of GRB 170817A and GW170817 constrains the speed gravity waves $c_T$ to be that light, which severely restricts landscape modified theories impact cosmological evolution universe. In this work, we investigate presence black hole hair in remaining viable respect constraint $c_T=1$. We focus mainly on scalar-tensor gravity, analyzing static, asymptotically flat holes Horndeski, Beyond Einstein-Scalar-Gauss-Bonnet, Chern-Simons theories. find all cases considered here,...

Through numerical simulations of a minimally coupled massive Klein-Gordon scalar field, we show that it is possible to grow hair on Schwarzschild black hole if one assumes an initial periodically time-varying but spatially homogeneous background. By "hair", mean non-trivial profile in the field. We find this emerges timescale related mass hole, with features particle. undertake and without backreaction metric see essential, qualitative remain consistent. also contrast results from higher...

Scalar fields around compact objects are of interest for scalar-tensor theories gravity and dark matter models consisting a massive scalar, e.g., axions. We study the behavior scalar field Kerr black hole with nontrivial asymptotic boundary conditions---both nonzero density angular momentum. Starting from an initial radially homogeneous configuration, cloud is accreted, which asymptotes to known stationary configurations over time. growth different parameters including spin, mass, momentum...

In general relativity (GR), gravitational waves (GWs) propagate the well-known plus and cross tensorial polarization modes, which are signature of a massless spin-2 field. However, diffraction GWs caused by intervening objects along line sight can cause apparent rise additional polarizations due to GW-curvature interactions. this paper, we continue analysis two authors present article, on lensing beyond geometric optics. particular, calculate effect pointlike lens in regime where its...

Cosmological models with a dynamical dark energy field typically lead to modified propagation of gravitational waves via an effectively time-varying coupling $G(t)$. The local variation this between the time emission and detection can be probed standard sirens. Here we discuss role that Lunar Laser Ranging (LLR) binary pulsar constraints play in prospects constraining $G(t)$ In particular, argue LLR constrains matter-matter $G_N(t)$, whereas pulsars sirens constrain quadratic kinetic gravity...

Abstract Low-energy alternatives to General Relativity (GR) generically modify the phase of gravitational waves (GWs) during their propagation. As detector sensitivities increase, it becomes key understand how these modifications affect GW higher modes and disentangle possible degeneracies with astrophysical phenomena. We apply a general formalism — WKB approach for solving analytically wave propagation in spatial domain modified dispersion relation (MDR). compare this applying stationary...

We study the parity-breaking higher-curvature gravity theory of Chern-Simons (CS), using Palatini formulation in which metric and connection are taken to be independent fields. first show that CS leads first-order derivative equations motion thus avoid typical instabilities formalism. As an initial application, we analyze cosmological propagation gravitational waves (GWs) gravity. that, due parity breaking, polarizations GWs suffer two effects during propagation: amplitude birefringence...

We propose and develop a general algorithm for finding the action cosmological perturbations which rivals conventional, gauge-invariant approach can be applied to theories with more than one metric. then apply it particular case of bigravity, focusing on Eddington-inspired Born-Infeld theory, show that we obtain nearly scale-invariant power spectrum both scalar tensor primordial quantum perturbations. Unfortunately, in minimal find tensor-to-scalar ratio is unacceptably large. discuss...

We analyse cosmological perturbations around a homogeneous and isotropic background for scalar-tensor, vector-tensor bimetric theories of gravity. Building on previous results, we propose unified view the effective parameters all these theories. Based this structure, explore viable space each family models by imposing absence ghosts gradient instabilities. then focus quasistatic regime confirm that can be approximated phenomenological two-parameter model described an Newton's constant...

It is standard practice to study the lensing of gravitational waves (GW) using geometric optics regime. However, in many astrophysical configurations this regime breaks down as wavelength becomes comparable Schwarzschild radius lens. We revisit GW including corrections beyond optics. propose a perturbative method for calculating these simply solving first order decoupled differential equations. behavior single ray and find that polarization plane defined smeared due diffraction effects,...

We consider gravitational wave (GW) sources with an associated electromagnetic (EM) counterpart and analyze the time delay between both signals in presence of lensing. If GWs have wavelengths comparable to Schwarzschild radius astrophysical lenses, they must be treated optics, whereas EM waves are typically well within approximation geometric optics. With concrete examples, we confirm that GW signal never arrives before its counterpart, if emitted at same time. However, during inspiral a...

The decay timescales of the quasinormal modes a massive scalar field have an intriguing behavior: they either grow or with increasing angular harmonic numbers $\ell$, depending on whether mass is small large. We identify properties effective potential that leads to this behavior and characterize it in detail. If non-minimally coupled, considered here, will leak into gravitational wave signal decaying times are comparable smaller than those typical General Relativity. Hence, these could be...

We study a previously largely unexplored branch of homogeneous and isotropic background solutions in ghost-free massive bigravity with consistent double matter coupling. For certain family parameters we find `self-inflated' FLRW cosmologies, i.e. an accelerated early-time period during the radiation-dominated era. In addition, these also display late-time closely mimicking GR cosmological constant. Interestingly, within this family, particular case $\beta_1=\beta_3=0$ gives bouncing where...