Detectability of Intermediate-Mass Black Holes in Multiband
**Gravitational** **Wave** Astronomy

**gravitational**

**waves**is a powerful tool for surveying the population of black holes across the universe. The first

**gravitational**

**wave**catalog from LIGO has detected black holes as heavy as $\sim50~M_\odot$, colliding when our Universe was about half its current age. However, there is yet no unambiguous evidence of black holes in the intermediate-mass range of $10^{2-5}~M_\odot$. Recent electromagnetic observations have hinted at the existence of IMBHs in the local universe; however, their masses are poorly constrained. The likely formation mechanisms of IMBHs are also not understood. Here we make the case that multiband

**gravitational**

**wave**astronomy --specifically, joint observations by space- and ground-based

**gravitational**

**wave**detectors-- will be able to survey a broad population of IMBHs at cosmological distances. By utilizing general relativistic simulations of merging black holes and state-of-the-art

**gravitational**waveform models, we classify three distinct population of binaries with IMBHs in the multiband era and discuss what can be observed about each. Our studies show that multiband observations involving the upgraded LIGO detector and the proposed space-mission LISA would detect the inspiral, merger and ringdown of IMBH binaries out to redshift ~2. Assuming that next-generation detectors, Einstein Telescope, and Cosmic Explorer, are operational during LISA's mission lifetime, we should have multiband detections of IMBH binaries out to redshift ~5. To facilitate studies on multiband IMBH sources, here we investigate the multiband detectability of IMBH binaries. We provide analytic relations for the maximum redshift of multiband detectability, as a function of black hole mass, for various detector combinations. Our study paves the way for future work on what can be learned from IMBH observations in the era of multiband

**gravitational**

**wave**astronomy.

5/10 relevant

arXiv

Multi-messenger **Gravitational**-**Wave** + High-Energy Neutrino Searches with
LIGO, Virgo, and IceCube

**gravitational**

**waves**and high-energy neutrinos provide important insights into the dynamics of and particle acceleration by black holes and neutron stars. Expand abstract.

**gravitational**

**waves**and high-energy neutrinos provide important insights into the dynamics of and particle acceleration by black holes and neutron stars. With LIGO's third observing period (O3), the number of

**gravitational**

**wave**detections has been substantially increased. The rapid identification of joint signals is crucial for electromagnetic follow-up observations of transient emission that is only detectable for short periods of time. High-energy neutrino direction can be reconstructed to sub-degree precision, making a joint detection far better localized than a standalone

**gravitational**-

**wave**signal. We present the latest sensitivity of joint searches and discuss the Low-Latency Algorithm for Multi-messenger Astrophysics (LLAMA) that combines LIGO/Virgo

**gravitational**-

**wave**candidates and searches in low-latency for coincident high-energy neutrinos from the IceCube Neutrino Observatory. We will further discuss future prospects of joint searches from the perspective of better understanding the interaction of relativistic and sub-relativistic outflows from binary neutron star mergers.

5/10 relevant

arXiv

An Optically Targeted Search for **Gravitational** **Waves** emitted by
Core-Collapse Supernovae during the First and Second Observing Runs of
Advanced LIGO and Advanced Virgo

**gravitational**-

**wave**transients associated with core-collapse supernovae observed within a source distance of approximately 20 Mpc during the first and second observing runs of Advanced LIGO and Advanced Virgo. No significant

**gravitational**-

**wave**candidate was detected. We report the detection efficiencies as a function of the distance for waveforms derived from multidimensional numerical simulations and phenomenological extreme emission models. For neutrino-driven explosions the distance at which we reach 50% detection efficiency is approaching 5 kpc, and for magnetorotationally-driven explosions is up to 54 kpc. However, waveforms for extreme emission models are detectable up to 28 Mpc. For the first time, the

**gravitational**-

**wave**data enabled us to exclude part of the parameter spaces of two extreme emission models with confidence up to 83%, limited by coincident data coverage. Besides, using \textit{ad hoc} harmonic signals windowed with Gaussian envelopes we constrained the

**gravitational**-

**wave**energy emitted during core-collapse at the levels of $4.27\times 10^{-4}\,M_\odot c^2$ and $1.28\times 10^{-1}\,M_\odot c^2$ for emissions at 235 Hz and 1304 Hz respectively. These constraints are two orders of magnitude more stringent than previously derived in the corresponding analysis using initial LIGO, initial Virgo and GEO~600 data.

7/10 relevant

arXiv

**Gravitational** **wave** emission from unstable accretion discs in tidal
disruption events

**Gravitational**

**waves**can be emitted by accretion discs if they undergo instabilities that generate a time varying mass quadrupole. In this work we investigate the

**gravitational**signal generated by a thick accretion disc of $1 M_{\odot}$ around a static super-massive black hole of $10^{6}M_{\odot}$, assumed to be formed after the tidal disruption of a solar type star. This torus has been shown to be unstable to a global non-axisymmetric hydrodynamic instability, the Papaloizou-Pringle instability, in the case where it is not already accreting and has a weak magnetic field. We start by deriving analytical estimates of the maximum amplitude of the

**gravitational**

**wave**signal, with the aim to establish its detectability by the Laser Interferometer Space Antenna (LISA). Then, we compare these estimates with those obtained through a numerical simulation of the torus, made with a 3D smoothed particle hydrodynamics code. Our numerical analysis shows that the measured strain is two orders of magnitude lower than the maximum value obtained analytically. However, accretion discs affected by the Papaloizou-Pringle instability may still be interesting sources for LISA, if we consider discs generated after deeply penetrating tidal disruptions of main sequence stars of higher mass.

5/10 relevant

arXiv

Simulating Binary Neutron Stars with Hybrid Equation of States:
**Gravitational** **Waves**, Electromagnetic Signatures, and Challenges for Numerical
Relativity

**gravitational**

**wave**emission after the moment of merger seem to hold and that the electromagnetic signatures connected to our chosen setup would not be bright enough to explain the kilonova associated to GW170817. Expand abstract.

**gravitational**

**wave**and electromagnetic signatures connected to the merger of two neutron stars allow us to test the nature of matter at supranuclear densities. Since the Equation of State governing the interior of neutron stars is only loosely constrained, there is even the possibility that strange quark matter exists inside the core of neutron stars. We investigate how strange quark matter cores affect the binary neutron star coalescence by performing numerical relativity simulations. Interestingly, the strong phase transition can cause a reduction of the convergence order of the numerical schemes to first order if the numerical resolution is not high enough. Therefore, an additional challenge is added in producing high-quality

**gravitational**

**wave**templates for Equation of States with a strong phase transition. Focusing on one particular configuration of an equal mass configuration consistent with GW170817, we compute and discuss the associated

**gravitational**

**wave**signal and some of the electromagnetic counterparts connected to the merger of the two stars. We find that existing waveform approximants employed for the analysis of GW170817 allow describing this kind of systems within the numerical uncertainties, which, however, are several times larger than for pure hadronic Equation of States, which means that even higher resolutions have been employed for an accurate

**gravitational**

**wave**model comparison. We also show that for the chosen Equation of State, quasi-universal relations describing the

**gravitational**

**wave**emission after the moment of merger seem to hold and that the electromagnetic signatures connected to our chosen setup would not be bright enough to explain the kilonova associated to GW170817.

8/10 relevant

arXiv

Real-Time Detection of **Gravitational** **Waves** from Binary Neutron Stars
using Artificial Neural Networks

**gravitational**

**waves**from binary black-hole mergers and, most recently, coalescing neutron stars started a new era of Multi-Messenger Astrophysics and revolutionize our understanding of the Cosmos. Expand abstract.

**gravitational**

**waves**from binary black-hole mergers and, most recently, coalescing neutron stars started a new era of Multi-Messenger Astrophysics and revolutionize our understanding of the Cosmos. Machine learning techniques such as artificial neural networks are already transforming many technological fields and have also proven successful in

**gravitational**-

**wave**astrophysics for detection and characterization of

**gravitational**-

**wave**signals from binary black holes. Here we use a deep-learning approach to rapidly identify transient

**gravitational**-

**wave**signals from binary neutron star mergers in noisy time series representative of typical

**gravitational**-

**wave**detector data. Specifically, we show that a deep convolution neural network trained on 100,000 data samples can rapidly identify binary neutron star

**gravitational**-

**wave**signals and distinguish them from noise and signals from merging black hole binaries. These results demonstrate the potential of artificial neural networks for real-time detection of

**gravitational**-

**wave**signals from binary neutron star mergers, which is critical for a prompt follow-up and detailed observation of the electromagnetic and astro-particle counterparts accompanying these important transients.

8/10 relevant

arXiv

**Gravitational** **Waves** from Holographic Neutron Star Mergers

**gravitational**waveforms. For the stars we construct hybrid equations of state (EoSs) with a standard nuclear matter EoS at low densities, transitioning to a state-of-the-art holographic EoS in the otherwise intractable high density regime. Depending on the transition density the characteristic frequencies in the spectrum produced from the hybrid EoSs are shifted to significantly lower values as compared to the pure nuclear matter EoS. The highest rest-mass density reached outside a possible black hole horizon is approximately $1.1 \cdot 10^{15}$ g/cm$^3$, which for the holographic model is below the density of the deconfined quark matter phase.

7/10 relevant

arXiv

Testing Seesaw and Leptogenesis with **Gravitational** **Waves**

**gravitational**

**waves**from the network of cosmic strings should be detectable. Expand abstract.

**gravitational**background. Achieving neutrino masses consistent with atmospheric and solar neutrino data, while avoiding non-perturbative couplings, requires right-neutrinos lighter than the typical scale of grand unification. This scale separation suggests a symmetry protecting the right handed neutrinos from getting a mass. Thermal leptogenesis would then require that such a symmetry be broken below the reheating temperature. We enumerate all such possible symmetries consistent with these minimal assumptions and their corresponding defects, finding that in many cases,

**gravitational**

**waves**from the network of cosmic strings should be detectable. Estimating the predicted

**gravitational**

**wave**background we find that future space-borne missions could probe the entire range relevant for thermal leptogenesis.

7/10 relevant

arXiv

Dark Matter, Dark Radiation and **Gravitational** **Waves** from Mirror Higgs
Parity

**gravitational**

**waves**that may be detected by future observations. Mirror glueballs decay to mirror photons giving dark radiation with $\Delta N_{\rm eff} \sim 0.03 - 0.4$. With a low reheat temperature after inflation, the $e'$ dark matter abundance is determined by freeze-in from the SM sector by either the Higgs or kinetic mixing portal.

7/10 relevant

arXiv

Impact of a Spinning Supermassive Black Hole on the Orbit and
**Gravitational** **Waves** of a Nearby Compact Binary

**wave**form from the BBH in one representative example and study its detectability by a milli-Hertz GW detector, such as the Laser Interferometer Space Antenna (LISA). Expand abstract.

7/10 relevant

arXiv