### Conveners

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#### OSB: DIV2

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#### OSB: DIV7

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#### OSB: Blue book

- Michele Maggiore
- Marica Branchesi (Gran Sasso Science Institute)
- Archisman Ghosh (Universiteit Gent)

#### OSB: Pre-Session

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Domain walls are topological defects that arise whenever a discrete symmetry is spontaneously broken. Being motivated in several Beyond the Standard Model scenarios, including axion-like particle models, domain walls are viable sources of a stochastic gravitational wave background with a broken power-law spectrum that could be detected by the near and far future third generation...

The frequency spectrum of the stochastic gravitational wave background (SGWB) from compact binary coalescences has a characteristic peak that depends on the specific features of the source population, notably the mass and redshift distribution. The underlying cosmology has an impact as well, mainly through the value of the Hubble parameter. The peak of the SGWB can be used as an observable,...

The multi-messenger (MM) observations of binary neutron star (BNS) mergers provide a novel approach to trace the distance-redshift relation, crucial for understanding the expansion history of the Universe and, consequently, testing the presence of Dark Energy (DE). While the gravitational wave (GW) signal offers a direct measure of the distance to the source, the combined efforts of wide-field...

Joint observations of gravitational-wave and GRB events are among the best standard siren prospects for cosmology. The actual possibility of obtaining an accurate measurement of the Hubble constant is however plagued by an intrinsic source of bias. This stems from the strong selection effect for the coincident detection of the GRB, which happens only for sources with particularly small...

Gravitational Waves (GWs) emitted by merging binaries of compact objects, when accompanied by an electromagnetic detection, can be used as โstandard sirensโ to probe the distance-redshift relation and the standard model of cosmology. However, we expect GW signals to be bent by the intervening matter field during their trajectory towards our detectors, a well-known phenomenon called...

The determination of the Hubble constant (H0) plays a crucial role in cosmology. Recent work has demonstrated the feasibility of constraining H0 through analysis of gravitational wave (GW) events without an electromagnetic (EM) counterparts and galaxy catalogues. This can be achieved using the publicly available gwcosmo package, with GW events from the GWTC3 catalogue and the GLADE+ galaxy...

Next-generation gravitational-wave detectors will provide unprecedented sensitivity to inspiraling binary neutron stars and black holes, enabling detections at the peak of star formation and beyond. However, the signals from these systems will last much longer than those in current detectors, and overlap in both time and frequency, leading to increased computational cost to search for them...

Relativistic jets accompany the collapse of massive stars, the merger of compact objects, or the accretion of gas in active galactic nuclei. They carry information about the central engine and generate electromagnetic radiation. No self-consistent simulations have been able to follow these jets from their birth at the black hole scale to the Newtonian dissipation phase, making the inference of...

Third-generation (3G) gravitational-wave (GW) detectors like the Einstein Telescope (ET) will observe binary black hole (BBH) mergers at redshifts up to z โผ 100. However, unequivocal determination of the origin of high-redshift sources will remain uncertain, due to the low signal-to-noise ratio (SNR) and poor estimate of their luminosity distance. This study proposes a machine learning...

The detection of a subsolar object in a compact binary merger is regarded as one of the smoking gun signatures of a population of primordial black holes (PBHs). We critically assess whether these systems could be distinguished from stellar binaries, for example composed of white dwarfs or neutron stars, which could also populate the subsolar mass range. At variance with PBHs, the...

Intermediate-mass black holes (IMBHs) are elusive objects that may represent the link between stellar-mass (BHs) and supermassive black holes (SMBHs). The current scarce observational evidence of IMBHs in the mass range 10^3-10^4 Msun leads to a natural question, are IMBHs a real category of BHs or, rather, do they represent exceptionally massive stellar BHs and light SMBHs?

In this talk, I...

The gravitational waves we observe today come from merging black holes that have formed throughout the entire Universe.

Their population properties encode valuable information about how stars form and evolve in galaxies very different from our own. They are also sensitive to, and can shed light on, the uncertain early history of element production in our Universe.

I will discuss the current...

One of the most exciting prospects of next-generation gravitational-wave (GW) detectors is their ability to detect double compact object (DCO) mergers at extremely high redshifts. These observations might enable us to use GW detections as an independent measure of the cosmic star formation rate out to unprecedentedly high redshifts. Measuring cosmic star formation with GW is (supposedly)...

Since the first detection of gravitational waves, the field of experimental gravitation is steadily working on improving the current detectors as well as developing new instruments in order to expand the range of observable frequencies and improve the reconstruction of GW direction and source parameters.

In such a context, the Astrometric Gravitational Wave Antenna (AstroGraWAnt, see for...

With the next generation of gravitational-wave observatories, the Einstein Telescope and Cosmic Explorer, we will have the opportunity to peer deeper into the gravitational-wave signal from merging neutron-star binaries and extract valuable information about the state of ultra-dense nuclear matter. In order to conduct this parameter inference reliably, we require waveform models that...

Three-nucleon forces are really important for understanding nuclear systems, including the dense matter found in neutron stars. In this study, we looked at different nuclear Hamiltonians that can accurately describe two-nucleon scattering data and properties of light nuclei, but differ in the three-nucleon interactions among neutrons. Although we didn't find any significantly improved...

In this talk, we present a systematic study of potential gravitational wave signatures produced by binary black hole coalescence, resulting in the production of an intermediate-mass black hole (IMBH). The event GW190521 represents the first direct evidence of the existence of IMBHs and suggests that more IMBHs might be detected when more data are collected, especially when more sensitivity is...

Gravitational-wave (GW) observations of binary black-hole (BBH) coalescences are expected to address outstanding questions in astrophysics, cosmology, and fundamental physics. Inference of BBH parameters relies on waveform models, and realizing the full discovery potential of upcoming facilities (such as the Einstein Telescope) hinges on the accuracy of these waveform models. Using...

The multi-messenger and multi-wavelength observations of the remarkable GW170817 event have significantly enhanced our comprehension of kilonova and relativistic-jet-related emissions following a binary neutron star (BNS) merger. While the outcomes of black hole-neutron star (BHNS) mergers remain less observationally constrained, leveraging insights from BNS mergers enables us to partially...

The detection of the gravitational wave (GW) signal GW170817 and the electromagnetic (EM) signal AT2017gfo confirmed the association between binary neutron star (BNS) mergers and kilonovae (KNe) and showed the potential of joint detection to unveil the nature of neutron stars and the nucleosynthesis of heavy elements in the Universe. The next-generation GW interferometers, such as the Einstein...

The Einstein Telescope (ET) will detect up to 10$^{5}$ binary neutron star system mergers (BNS) per year beyond z~3, clearly revolutionizing gravitational waves (GW) multi-messenger (MM) astrophysics. The optical-near infrared electromagnetic (EM) counterparts of such BNS will likely be faint and to be found within the large GW signals error regions, among a huge number of contaminants. The...

The huge luminosity, the redshift distribution extending at least up to z~10 and the association with the explosive death of very massive stars make long GRBs extremely powerful probes for investigating the early Universe (pop-III stars, cosmic re-ionization, SFR and metallicity evolution up to the โcosmic dawnโ) and measuring cosmological parameters. At the same time, as demonstrated by the...

The improved sensitivity of the Einstein Telescope increases the observable volume of compact binary systems and extends the time window in which the inspiral phase is measurable. Neural Networks (NNs) can efficiently analyze the vast amount of data by reducing computational costs and runtime. This talk presents a fast Binary Black Hole parameter reconstruction by applying a conventional...

In-depth understanding of correlated noise effects is critical for optimizing third-generation gravitational-wave detectors such as the Einstein Telescope. This presentation unfolds in two parts. In the first part, we explore the statistical formulation of the likelihood function, integrating correlated noise into parameter estimation for detector networks. Our analysis demonstrates that...

Due to its speed after training, machine learning is often envisaged as a solution to a manifold of the issues faced in gravitational-wave astronomy. Demonstrations have been given for various applications in gravitational-wave data analysis. In this work, we focus on a challenging problem faced by third-generation detectors: parameter inference for overlapping signals. Due to the high...

The gravitational waves emitted by binary neutron star mergers contain information on nuclear matter above saturation density. However, extracting this information and conducting parameter estimation remains computationally challenging and expensive. Wong et al. introduced Jim, a parameter estimation pipeline that combines relative binning and JAX features, such as hardware acceleration and...

The increased sensitivity of the Einstein Telescope will lead to a significant increase in the number of gravitational wave signals we can detect. In addition, it will allow us to observe the gravitational wave signals for a longer duration. While both of these factors, a large number of signals and longer signals can open windows to previously unexplored science cases, they also introduce the...

Data analysis of gravitational wave events will face many challenges in the ET era. The improvement of a factor 10 in the sensitivity translates to ~10^5 events/year while the broader sensitivity range at low frequencies will lead to longer-duration signals. A larger number of signals will lead to overlapping signals that will therefore amplify the computational burden, posing complex...

Next-generation gravitational wave interferometers, such as the Einstein Telescope, will observe an unprecedented volume of events. This requires analysis tools that can deal with large datasets. Our software GWFish utilizes Fisher matrix analysis, which is currently the state-of-the-art method in the field and can effectively evaluate detector performance.

We now want to present an...

The Fisher information matrix (FIM) formalism is nowadays widely used to forecast the parameter estimation (PE) capabilities of future GW detectors to avoid the high computational cost of Bayesian PE analyses.

Unfortunately, this formalism is known to fail in some regions of the GW parameter space, especially when strong parameter degeneracies are present. One of the best-known examples is...