A new method to test the cosmic distance duality relation using the
strongly lensed **gravitational** **waves**

**gravitational**

**waves**provide a unique way to test the cosmic distance duality relation. Expand abstract.

**gravitational**

**waves**. The spontaneous observations of image positions and the relative time delay between different images, the redshift measurements of the lens and source, together with the mass modelling of the lens galaxy, provide the angular diameter distance to the source. On the other hand, from the observation of

**gravitational**

**wave**signals the luminosity distance to the source can be obtained. Thus, the strongly lensed

**gravitational**

**waves**provide a unique way to test the cosmic distance duality relation.

10/10 relevant

arXiv

Surface **gravity** **waves** propagating in a rotating frame: the Ekman-Stokes
instability

**gravity**

**waves**propagate in a rotating frame. Expand abstract.

**gravity**

**waves**propagate in a rotating frame. The Stokes drift associated to the uniform

**wave**field, together with global rotation, drives a mean flow in the form of a horizontally invariant Ekman-Stokes spiral. We show that the latter can be subject to an instability that triggers the appearance of an additional horizontally-structured cellular flow. We determine the instability threshold numerically, in terms of the Rossby number Ro associated to the Stokes drift of the

**waves**and the Ekman number E. We confirm the numerical results through asymptotic expansions at both large and low Ekman number. At large E the instability reduces to that of a standard Ekman spiral driven by the

**wave**-induced surface stress instead of a wind stress, while at low E the Stokes-drift profile crucially determines the shape of the unstable mode. In both limits the instability threshold asymptotes to an Ekman-number-independent critical Rossby number, which in both cases also corresponds to a critical Reynolds number associated to the Lagrangian base-flow velocity profile. Parameter values typical of ocean swell fall into the low-E unstable regime: the corresponding "anti-Stokes" flows are unstable, with possible consequences for particle dispersion and mixing.

9/10 relevant

arXiv

Standard Sirens as a novel probe of dark energy

**gravitational**

**waves**via an effectively time-varying

**gravitational**coupling $G(t)$. The local variation of this coupling between the time of emission and detection can be probed with standard sirens. Here we discuss the role that Lunar Laser Ranging (LLR) and binary pulsar constraints play in the prospects of constraining $G(t)$ with standard sirens. In particular, we argue that LLR constrains the matter-matter

**gravitational**coupling $G_N(t)$, whereas binary pulsars and standard sirens constrain the quadratic kinetic

**gravity**self-interaction $G_{gw}(t)$. Generically, these two couplings could be different in alternative cosmological models, in which case LLR constraints are irrelevant for standard sirens. We use the Hulse-Taylor pulsar data and show that observations are highly insensitive to time variations of $G_{gw}(t)$, and we thus conclude that future

**gravitational**

**waves**data will become the best probe to test $G_{gw}(t)$, and will hence provide novel constraints on dynamical dark energy models.

4/10 relevant

arXiv

Empirical relations for **gravitational**-**wave** asteroseismology of binary
neutron star mergers

**gravitational**

**wave**frequency in the post-merger phase of binary neutron star mergers. The relations determine neutron star radii and tidal deformabilities for specific neutron star masses with consistent accuracy and depend only on two observables: the post-merger peak frequency $f_{\rm peak}$ and the chirp mass $M_{\rm chirp}$. The former could be measured with good accuracy from

**gravitational**

**waves**emitted in the post-merger phase using next-generation detectors, whereas the latter is already obtained with good accuracy from the inspiral phase with present-day detectors. Our main data set consists of a

**gravitational**

**wave**catalogue obtained with CFC/SPH simulations. We also extract the $f_{\rm peak}$ frequency from the publicly available CoRe data set, obtained through grid-based GRHD simulations and find good agreement between the extracted frequencies of the two data sets. As a result, we can construct empirical relations for the combined data sets. Furthermore, we investigate empirical relations for two secondary peaks, $f_{2-0}$ and $f_{\rm spiral}$, and show that these relations are distinct in the whole parameter space, in agreement with a previously introduced spectral classification scheme. Finally, we show that the spectral classification scheme can be reproduced using machine-learning techniques.

4/10 relevant

arXiv

Growth Rate of **Gravity** **Wave** Amplitudes Observed in Sodium Lidar Density Profiles and Nightglow Image Data

**gravity**

**waves**. Expand abstract.

**gravity**

**waves**were estimated and compared from multiple instrument measurements carried out in Brazil.

**Wave**dynamic parameters were obtained from sodium density profiles from lidar observations carried out in Sao Jose dos Campos (23°S, 46°W), while all-sky images of multiple airglow layers provided amplitudes and parameters of

**waves**over Cachoeira Paulista (23°S, 45°W). Growth rates of

**gravity**

**wave**amplitudes from lidar and airglow imager data were consistent with dissipative

**wave**behavior. Only a small amount of the observed

**wave**events presented freely propagating behavior. Part of the observed

**waves**presented saturated amplitude. The general saturated/damped behavior is consistent with diffusive filtering processes imposing limits to amplitude growth rates of the observed

**gravity**

**waves**.

10/10 relevant

Preprints.org

**Gravitational** **waves** and higher dimensions: Love numbers and Kaluza-Klein
excitations

**Gravitational**-

**wave**(GW) observations provide a wealth of information on the nature and properties of black holes. Among these, tidal Love numbers or the multipole moments of the inspiralling and final objects are key to a number of constraints. Here, we consider these observations in the context of higher-dimensional scenarios, with flat large extra dimensions. We show that -- as might be anticipated, but not always appreciated in the literature -- physically motivated set-ups are unconstrained by

**gravitational**-

**wave**data. Dynamical processes that do not excite the Kaluza-Klein (KK) modes lead to a signal identical to that in four-dimensional general relativity in vacuum . In addition, any possible excitation of the KK modes is highly suppressed relative to the dominant quadrupolar term; given existing constraints on the extra dimensions and the masses of the objects seen in

**gravitational**-

**wave**observations, KK modes appear at post-Newtonian order $\sim 10^{11}$. Finally, we re-compute the tidal Love numbers of spherical black holes in higher dimensions. We confirm that these are different from zero, but comparing with previous computations we find a different magnitude and sign.

7/10 relevant

arXiv

Crest speeds of unsteady surface water **waves**

**gravity**

**waves**become less dispersive, either as they steepen or as they propagate over finite water depths. Expand abstract.

**waves**are assumed to match their phase velocities. However, this is generally not the case for natural

**waves**within unsteady

**wave**groups. This motivates our study, which presents new insights into the generic behavior of crest speeds of linear to highly nonlinear unsteady

**waves**. While our major focus is on

**gravity**

**waves**where a generic crest slowdown occurs cyclically, results for capillary-dominated

**waves**are also discussed, for which crests cyclically speed up. This curious phenomenon arises when the theoretical constraint of steadiness is relaxed, allowing

**waves**to change their form, or shape. In particular, a kinematic analysis of both simulated and observed open ocean

**gravity**

**waves**reveals a forward-to-backward leaning cycle for each individual crest within a

**wave**group. This is clearly manifest during the focusing of dominant

**wave**groups essentially due to the dispersive nature of

**waves**. It occurs routinely for focusing linear (vanishingly small steepness)

**wave**groups, and it is enhanced as the

**wave**spectrum broadens. It is found to be relatively insensitive to the degree of phase coherence and focusing of

**wave**groups. The nonlinear nature of

**waves**limits the crest slowdown. This reduces when

**gravity**

**waves**become less dispersive, either as they steepen or as they propagate over finite water depths. This is demonstrated by numerical simulations of the unsteady evolution of 2D and 3D dispersive

**gravity**

**wave**packets in both deep and intermediate water depths, and by open ocean space-time measurements.

8/10 relevant

arXiv

**Gravitational** **wave** stochastic background from cosmological particle
decay

**gravitational**

**waves**(GW) via a new "memory effect" mechanism. Expand abstract.

**gravitational**

**waves**(GW) via a new "memory effect" mechanism. We calculate the spectral amplitude and slope of the resulting background, which is frequency-independent (flat). We discuss its potential observability and show that the resulting background might dominate the cosmological GW background at frequencies above about 10 GHz. Penrose has proposed a cosmological model in which dark matter particles have the Planck mass and decay into two gravitons [arXiv:1707.04169]. For these, the spectrum has an additional "direct" contribution from the decay products, which we also calculate. At low frequencies, this direct contribution also has a flat spectrum but with a much smaller amplitude than the memory part.

4/10 relevant

arXiv

**Wave** heating from proto-neutron star convection and the core-collapse
supernova explosion mechanism

**waves**can also carry energy from the PNS to the shock. We show that

**gravity**

**waves**excited by core PNS convection can couple with outgoing acoustic

**waves**that present an appreciable source of energy and pressure in the post-shock region. Using one-dimensional simulations, we estimate the

**gravity**

**wave**energy flux excited by PNS convection and the fraction of this energy transmitted upward to the post-shock region as acoustic

**waves**. We find

**wave**energy fluxes near $10^{51}\,\mathrm{erg}\,\mathrm{s}^{-1}$ are likely to persist for $\sim1\,\mathrm{s}$ post-bounce. The

**wave**pressure on the shock may exceed $10\%$ of the thermal pressure, potentially contributing to shock revival and, subsequently, a successful and energetic explosion. We also discuss how future simulations can better capture the effects of waves, and more accurately quantify

**wave**heating rates.

7/10 relevant

arXiv

Two dimensional **gravity** **waves** at low regularity I: Energy estimates

**wave**equations in two space dimensions. Expand abstract.

**wave**equations in two space dimensions. Our focus here is on sharp cubic energy estimates. Precisely, we introduce and develop the techniques to prove a new class of energy estimates, which we call \emph{balanced cubic estimates}. This yields a key improvement over the earlier cubic estimates of Hunter-Ifrim-Tataru [12], while preserving their scale invariant character and their position-velocity potential holomorphic coordinate formulation. Even without using any Strichartz estimates, these results allow us to significantly lower the Sobolev regularity threshold for local well-posedness, drastically improving earlier results obtained by Alazard-Burq-Zuily [3, 4], Hunter-Ifrim-Tataru [12] and Ai [2].

7/10 relevant

arXiv