Multi-messenger astronomy with very-high-energy gamma-ray observations

**gravitational**

**waves**, is now an established reality. Expand abstract.

**gravitational**waves, is now an established reality. Within this emerging discipline we argue that very-high-energy (VHE) gamma-ray observations play a special role. We discuss the recent progress on explosive transients, the connections between neutrino and gamma-ray astronomy and the search for search for dark matter. Finally, the experimental prospects for the next decade in the VHE gamma-ray field are summarised.

4/10 relevant

arXiv

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.

4/10 relevant

arXiv

Impact of subdominant modes on the interpretation of **gravitational**-wave
signals from heavy binary black hole systems

**gravitational**

**wave**models have been developed to include multiple harmonic modes thereby enabling for the first time fully Bayesian inference studies including higher modes to be performed. Using one recently-developed numerical relativity surrogate model, NRHybSur3dq8, we investigate the importance of higher modes on parameter inference of coalescing massive binary black holes. We focus on examples relevant to the current three-detector network of observatories, with detector-frame masses and signal amplitudes consistent with plausible candidates for the next few observing runs. We show that for such systems the higher mode content will be important for interpreting coalescing binary black holes, reducing systematic bias, and computing properties of the remnant object. For asymmetric binaries with mass ratios $q>1$, higher modes are critical, and their omission usually produces substantial parameter biases. Even for comparable-mass binaries and at low signal amplitude, the omission of higher modes can influence posterior probability distributions. We discuss the impact of our results on source population inference and self-consistency tests of general relativity.

7/10 relevant

arXiv

Revisiting slow-roll dynamics and the tensor tilt in general single-field inflation

**gravitational**

**waves**can be blue in inflation with the Gauss-Bonnet term, where the potential term is dominant and slow-roll conditions as well as the stability conditions are satisfied. Expand abstract.

**gravitational**

**wave**spectrum from potential-driven slow-roll inflation in the Horndeski theory. In Kamada et al. (2012), it was claimed that a blue

**gravitational**

**wave**spectrum cannot be obtained from stable potential-driven slow-roll inflation within the Horndeski framework. However, it has been demonstrated that the spectrum of primordial

**gravitational**

**waves**can be blue in inflation with the Gauss-Bonnet term, where the potential term is dominant and slow-roll conditions as well as the stability conditions are satisfied. To fill in this gap, we clarify where the discrepancy is coming from. We extend the formulation of Kamada et al. (2012) and show that a blue

**gravitational**

**wave**spectrum can certainly be generated from stable slow-roll inflation if some of the conditions previously imposed on the form of the free functions in the Lagrangian are relaxed.

7/10 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

**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. Expand abstract.

**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.

7/10 relevant

arXiv

COSMIC Variance in Binary Population Synthesis

**gravitational**

**wave**observatories are inspiraling and/or merging compact binaries. Simulations of large compact binary populations serve to both predict and inform observations of

**gravitational**

**wave**sources and their progenitors. Binary population synthesis (BPS) is a tool that balances physical modeling with simulation speed to produce large binary populations on timescales of $\sim$days. We present a new, openly developed, BPS suite: COSMIC which is designed to simulate compact binary populations and their progenitors. As a proof of concept, we simulate the Galactic population of compact binaries and their

**gravitational**

**wave**signal observable by the Laser Interferometer Space Antenna (LISA). We find that $\sim10^8$ compact binaries reside in the Milky Way today, while $\sim10^4$ of them may be resolvable by LISA.

4/10 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%.

10/10 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