Constraining the abundance of primordial black holes with **gravitation**al
lensing of **gravitational** **waves** at LIGO frequencies

**gravitational**

**waves**will show interference effects. Expand abstract.

**Gravitational**

**waves**from binary black holes that are gravitationally lensed can be distorted by small microlenses along the line of sight. Microlenses with masses of a few tens of solar masses, and that are close to a critical curve in the lens plane, can introduce a time delay of a few millisecond. Such time delay would result in distinctive interference patterns in the

**gravitational**

**wave**that can be measured with current experiments such as LIGO/Virgo. We consider the particular case of primordial black holes with masses between 5 and 50 solar masses acting as microlenses. We study the effect of a population of primordial black holes constituting a fraction of the dark matter, and contained in a macrolens (galaxy or cluster), over

**gravitational**

**waves**that are being lensed by the combined effect of the macrolens plus microlenses. We find that at the typical magnifications expected for observed GW events, the fraction of dark matter in the form of compact microlenses, such as primordial black holes, can be constrained to percent level. Similarly, if a small percentage of the dark matter is in the form of microlenses with a few tens of solar masses, at sufficiently large magnification factors, all

**gravitational**

**waves**will show interference effects. These effects could have an impact on the inferred parameters. The effect is more important for macroimages with negative parity, which usually arrive after the macroimages with positive parity.

10/10 relevant

arXiv

ELGAR -- a European Laboratory for **Gravitation** and Atom-interferometric
Research

**Gravitational**

**Waves**(GWs) were observed for the first time in 2015, one century after Einstein predicted their existence. There is now growing interest to extend the detection bandwidth to low frequency. The scientific potential of multi-frequency GW astronomy is enormous as it would enable to obtain a more complete picture of cosmic events and mechanisms. This is a unique and entirely new opportunity for the future of astronomy, the success of which depends upon the decisions being made on existing and new infrastructures. The prospect of combining observations from the future space-based instrument LISA together with third generation ground based detectors will open the way towards multi-band GW astronomy, but will leave the infrasound (0.1 Hz to 10 Hz) band uncovered. GW detectors based on matter

**wave**interferometry promise to fill such a sensitivity gap. We propose the European Laboratory for

**Gravitation**and Atom-interferometric Research (ELGAR), an underground infrastructure based on the latest progress in atomic physics, to study space-time and

**gravitation**with the primary goal of detecting GWs in the infrasound band. ELGAR will directly inherit from large research facilities now being built in Europe for the study of large scale atom interferometry and will drive new pan-European synergies from top research centers developing quantum sensors. ELGAR will measure GW radiation in the infrasound band with a peak strain sensitivity of $4.1 \times 10^{-22}/\sqrt{\text{Hz}}$ at 1.7 Hz. The antenna will have an impact on diverse fundamental and applied research fields beyond GW astronomy, including gravitation, general relativity, and geology.

5/10 relevant

arXiv

**Gravitational** **Waves** from Phase Transition in Minimal SUSY $U(1)_{B-L}$
Model

**gravitational**

**waves**in $O(10)$-$O(100)$ Hz range if $\beta_{\rm n}/H_{\rm n}=1000$, which can be detected by ground-based detectors. Meanwhile, supersymmetry (SUSY) may play a crucial role in the dynamics of such high-scale $U(1)$ gauge symmetry breaking, because SUSY breaking scale is expected to be at TeV to solve the hierarchy problem. In this paper, we study the phase transition of $U(1)$ gauge symmetry breaking in a SUSY model in the SUSY limit. We consider a particular example, the minimal SUSY $U(1)_{B-L}$ model. We derive the finite temperature effective potential of the model in the SUSY limit, study a $U(1)_{B-L}$-breaking phase transition, and estimate

**gravitational**

**waves**generated from it.

10/10 relevant

arXiv

Flatly foliated relativity

**gravity**without

**gravitational**

**waves**. In FFR, a positive cosmological constant implies several interesting properties which do not follow in GR: the metric equations are elliptic on each euclidean slice, there exists a unique vacuum solution among those spherically symmetric at infinity, and there exists a geometric way to define the arrow of time. Furthermore, as

**gravitational**

**waves**do not exist in FFR, there are simple analogs to the positive mass theorem and Penrose-type inequalities. Importantly, given that

**gravitational**

**waves**have a negligible effect on the curvature of spacetime, and that the universe appears to be locally flat, FFR may be a good approximation of GR. Moreover, FFR still admits many notable features of GR including the big bang, an accelerating expansion of the universe, and the Schwarzschild spacetime. Lastly, FFR is already known to have an existence theory for some simplified cases, which provokes an interesting discussion regarding the possibility of a more general existence theory, which may be relevant to understanding existence of solutions to GR.

5/10 relevant

arXiv

On ab initio closed-form expressions for **gravitational** **waves**

**gravitational**

**waves**emitted by binary systems. Expand abstract.

**gravitational**

**waves**emitted by binary systems. Our expressions are built from numerical surrogate models based on numerical relativity simulations, which have been shown to be essentially indistinguishable from each other, with the advantage that our expressions can be written explicitly in a few lines. The key new ingredient in this approach is symbolic regression through genetic programming. The minimum overlap obtained in the proof of concept here presented, compared to ground truth solutions, is 99%.

8/10 relevant

arXiv

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