**Gravity** **waves** in parity-violating Copernican Universes

**gravitational**

**wave**fluctuations in the parity violating branch. If the dynamics are ruled solely by the Euler-type term, then linear tensor mode perturbations are entirely undetermined, hinting at a new type of gauge invariance. The Pontryagin term not only permits for phenomenologically sounder background solutions (as found in previous literature), but for realistic propagation of

**gravitational**

**wave**modes. These have the general property that the right and left handed

**gravitational**

**waves**propagate with different speeds. More generally they imply modified dispersion relations for the graviton, with both parity violating and non-violating deformations, including an effective mass for both

**gravitational**

**wave**polarizations. We discuss the observational constraints and predictions of these theories.

9/10 relevant

arXiv

Electromagnetic precursors to **gravitational** **wave** events: Numerical
simulations of flaring in pre-merger binary neutron star magnetospheres

**gravitational**

**waves**from neutron star merger events has opened up a new field of multi-messenger astronomy linking

**gravitation**al

**wave**s events to short-gamma ray bursts and kilonova afterglows. Expand abstract.

**gravitational**

**waves**from neutron star merger events has opened up a new field of multi-messenger astronomy linking

**gravitational**

**waves**events to short-gamma ray bursts and kilonova afterglows. A further - yet to be discovered - electromagnetic counterpart is precursor emission produced by the non-trivial interaction of the magnetospheres of the two neutron stars prior to merger. By performing special-relativistic force-free simulations of orbiting neutron stars we discuss the effect of different magnetic field orientations and show how the emission can be significantly enhanced by differential motion present in the binary, either due to stellar spins or misaligned stellar magnetospheres. We find that the built-up of twist in the magnetic flux tube connecting the two stars can lead to the repeated emission of powerful flares for a variety of orbital configurations. We also discuss potential coherent radio emission mechanisms in the flaring process.

5/10 relevant

arXiv

Cosmological constraints on dark energy in light of **gravitational** **wave**
bounds

**Gravitational**

**wave**(GW) constraints have recently been used to significantly restrict models of dark energy and modified

**gravity**. New bounds arising from GW decay and GW-induced dark energy instabilities are particularly powerful in this context, complementing bounds from the observed speed of GWs. We discuss the associated linear cosmology for Horndeski

**gravity**models surviving these combined bounds and compute the corresponding cosmological parameter constraints, using CMB, redshift space distortion, matter power spectrum and BAO measurements from the Planck, SDSS/BOSS and 6dF surveys. The surviving theories are strongly constrained, tightening previous bounds on cosmological deviations from $\Lambda{}$CDM by over an order of magnitude. We also comment on general cosmological stability constraints and the nature of screening for the surviving theories, pointing out that a raised strong coupling scale can ensure compatibility with

**gravitational**

**wave**constraints, while maintaining a functional Vainshtein screening mechanism on solar system scales. Finally, we discuss the quasi-static limit as well as (constraints on) related observables for near-future surveys.

4/10 relevant

arXiv

Signatures of Extended Theories of **Gravity** in Black Hole Oscillations

**gravitational**perturbations will however differ between different theories of

**gravity**. Future precision tests involving

**gravitational**

**waves**from oscillating black holes, such as identifications of the quasi-normal mode spectrum from ring-down, will thus be able to probe the underlying theory, even if the object is Kerr. Here, we write down the equations governing metric perturbations of a Kerr black hole in $f(R)$

**gravity**in a form that is more conducive to numerical study.

4/10 relevant

arXiv

Asymptotic Shear and the Intrinsic Geometry of Null-Infinity

**gravitational**

**waves**and the non-uniqueness of flat null-normal tractor connections correspond to the "degeneracy of

**gravity**vacuum" that has been extensively discussed in the literature. Expand abstract.

**gravitational**

**waves**can be understood to be a generalisation of the tractor calculus of conformal manifolds adapted to the case of degenerate conformal metrics. It follows that the whole formalism is, by construction, manifestly conformally invariant. We first show that a choice of asymptotic shear amounts to a choice of linear differential operator of order two on the bundle of scales of null-infinity. We refer to these operators as Poincar\'e operators. We then show that Poincar\'e operators are in one-to-one correspondence with a particular class of tractor connections which we call "null-normal" (they generalise the normal tractor connection of conformal geometry). The tractor curvature encodes the presence of

**gravitational**

**waves**and the non-uniqueness of flat null-normal tractor connections correspond to the "degeneracy of

**gravity**vacuum" that has been extensively discussed in the literature. This work thus brings back the investigation of the radiative phase space of

**gravity**to the study of (Cartan) connections and associated bundles. This allows, in particular, to proliferate invariants of the phase space.

4/10 relevant

arXiv

Nonsingular Ekpyrotic Cosmology with a Nearly Scale-Invariant Spectrum
of Cosmological Perturbations and **Gravitational** **Waves**

**gravitational**

**waves**into an almost scale-invariant one. Expand abstract.

**gravitational**

**waves**into an almost scale-invariant one. The scalar and tensor tilts are predicted to be the same, in contrast to the predictions from the "String Gas Cosmology" scenario. The amplitude of the

**gravitational**

**wave**spectrum depends on the ratio of the string scale to the Planck scale and may be in reach of upcoming experiments.

7/10 relevant

arXiv

Core-Collapse Supernova **Gravitational**-**Wave** Search and Deep Learning
Classification

**gravitational**

**waves**emitted by core-collapse supernova (CCSN) explosions, using a convolutional neural network (CNN) combined with an event trigger generator known as

**Wave**let Detection Filter (WDF). Expand abstract.

**gravitational**

**waves**emitted by core-collapse supernova (CCSN) explosions, using a convolutional neural network (CNN) combined with an event trigger generator known as Wavelet Detection Filter (WDF). We employ both a 1-D CNN search using time series

**gravitational**-

**wave**data as input, and a 2-D CNN search with time-frequency representation of the data as input. To test the accuracies of our 1-D and 2-D CNN classification, we add CCSN waveforms from the most recent hydrodynamical simulations of neutrino-driven core-collapse to simulated Gaussian colored noise with the Virgo interferometer and the planned Einstein Telescope sensitivity curve. We find classification accuracies, for a single detector, of over 95% for both 1-D and 2-D CNN pipelines. For the first time in machine learning CCSN studies, we add short duration detector noise transients to our data to test the robustness of our method against false alarms created by detector noise artifacts. Further to this, we show that the CNN can distinguish between different types of CCSN waveform models.

4/10 relevant

arXiv

**Gravitational** **waves** in Modified Gauss-Bonnet **gravity**

**gravitational**

**waves**in modified Gauss-Bonnet

**gravity**. Applying the metric perturbation around a cosmological background, we obtain explicit expressions for the

**wave**equations. It is shown that the speed of the traceless mode is equal to the speed of light. An additional massive scalar mode appears in the propagation of the

**gravitational**

**waves**. To find phenomena beyond the general relativity the scalar mode mass is calculated as a function of the background curvature in some typical models.

10/10 relevant

arXiv

Primordial black holes and **gravitational** **waves** from parametric
amplification of curvature perturbations

**gravitational**

**waves**fall in the frequency band measurable for the pulsar timing array and the space-based

**gravitation**al

**wave**detectors. Expand abstract.

**gravitational**

**waves**. The mass of primordial black holes and frequency of the induced

**gravitational**

**waves**depend on the model parameters. The primordial black hole could constitute all dark matter or a fraction of dark matter in the Universe, and corresponding stochastic

**gravitational**

**waves**fall in the frequency band measurable for the pulsar timing array and the space-based

**gravitational**

**wave**detectors.

10/10 relevant

arXiv

How capillarity affects the propagation of elastic **waves** in soft gels

**waves**propagating at the interface of soft solids can be altered by the presence of external forces such as capillarity or

**gravity**. Expand abstract.

**waves**propagating at the interface of soft solids can be altered by the presence of external forces such as capillarity or

**gravity**. We measure the dispersion relation of

**waves**at the free surface of agarose gels with great accuracy, revealing the existence of multiple modes as well as an apparent dispersion. We disentangle the role of capillarity and elasticity by considering the 3D nature of mechanical waves, achieving quantitative agreement between theoretical predictions and experiments. Notably, our results show that capillarity plays an important role for wavenumbers much smaller than expected from balancing elastic and capillary forces. We further confirm the efficiency of our approach by including the effect of

**gravity**in our predictions and quantitatively comparing it to experiments.

4/10 relevant

arXiv