4th Einstein Telescope Annual Meeting

11 Nov 2025, 09:00 → 14 Nov 2025, 13:00 Europe/Rome

Opatija, Croatia

The 4th Einstein Telescope Annual Meeting presents an opportunity to discuss key aspects of the ET collaboration and design.

Hosted by the University of Rijeka, the event will be held at the Drago Gervais multifunctional hall, located in the heart of the nearby Opatija.

The meeting is open to all members of the ET collaboration, beginning on the morning of Tuesday, November 11, and concluding on Friday, November 14 at lunchtime.

 

 

Participants can join all sessions online via Zoom. Zoom links will be provided as attachments in the session timetable.

Social events:

    Early Career Researchers Meeting: November 11
    Conference Dinner: November 13

Local Organizing Committee:

   Marin Karuza, Marina Manganaro, Nenad Kralj, Karlo Veličan, Jonatan Lerga from University of Rijeka and  Željka Bošnjak from University of Zagreb

We look forward to welcoming all participants, both in person and online, for a productive and engaging meeting!

The registration is not needed for online participants.

Tuesday 11 November

Plenary: Plenary 1: Welcome and ET Collaboration Overview

Plenary 1: Welcome and ET Collaboration Overview

Conveners: Harald Lueck, Michele Punturo (INFN)

1 Welcome by local authorities

2 LOC practical indications

Speaker: Marin Karuza

3 ET Collaboration: Activities report

Speakers: Harald Lueck, Michele Punturo (INFN)

4 ET collaboration status Report, FNR survey, new CB chair

Speaker: Eugenio Coccia

5 Ombudsperson

Speaker: Sebastian Steinlechner

Coffee

Plenary: Plenary 2: ET Collaboration Activities

Plenary 1: Welcome and ET Collaboration Overview

Conveners: Harald Lueck, Michele Punturo (INFN)

6 Preliminary TDR

Speakers: Jan Harms, Stefan Hild

7 Data access policy

Speaker: Michele Punturo (INFN)

8 Training and Mentorship

9 Poster Sparklers

Lunch

ET-PP WP4&9: ET-PP

Convener: maria marsella (Sapienza University, Rome)

Instrument Science (ISB): ISB - Contributed talks

Conveners: Jan Harms, Stefan Hild

Observational Science (OSB): Update from divisions & OSB roadmap

Conveners: Archisman Ghosh (Universiteit Gent), Marica Branchesi, Michele Maggiore

10 Div 1 update

11 Div 2 update

12 Div 3 update

13 Div 4 update

14 Div 5 update

15 Div 6 update

16 Div 7 update

17 Div 8 update

18 Div 9 update

19 Div 10 update

20 Roadmap discussion

Site Preparation & Characterization (SCB)

Conveners: Domenico D'Urso, Dr Wim Walk (Nikhef)

Coffee

Instrument Science (ISB): ISB - Contributed talks

Conveners: Jan Harms, Stefan Hild

Observational Science (OSB): Divs 1, 2 contributions

Conveners: Archisman Ghosh (Universiteit Gent), Marica Branchesi, Michele Maggiore

21 Beyond GR tests with Einstein Telescope

Gravitational waves from compact binary coalescences (CBCs) have become a robust and powerful tool for testing General Relativity (GR), in fact, to date, the LIGO-Virgo-KAGRA collaboration has provided significant consistency tests of GR.
In this talk, I will present forecasts for the precision with which GR can be tested using third-generation interferometers, such as the Einstein Telescope. The anticipated large number of detected sources makes full Bayesian analyses computationally infeasible. To address this, we employ the newly released GWJulia code, which enables studies of large CBC populations using the Fisher information formalism.
Using this framework, we explore the constraints the Einstein Telescope could place on post-Newtonian (PN) coefficients within a hierarchical Bayesian approach. In addition, we will discuss the number of events required to identify deviations from GR at various PN orders and under different detector configurations.

Speaker: Andrea Begnoni

22 Spin-induced quadrupole moment test for eccentric compact binaries

Testing the binary black hole nature of compact binaries relies on the “no-hair” conjecture, which posits that a Kerr black hole's properties are fully characterized by its mass and spin. This conjecture underpins tests applied to circular compact binaries detected by gravitational wave (GW) detectors, where the quadrupole moment depends solely on mass and spin. In contrast, exotic compact objects may require additional parameters, such as the equation of state, encoded in spin-induced quadrupole moments. Extending previous tests to binaries on eccentric orbits, we use Fisher matrix analysis to quantify parameter uncertainties and assess eccentricity's impact. Next-generation detectors like the Einstein Telescope and Cosmic Explorer, with their enhanced low-frequency sensitivity, will make these tests more powerful, allowing for tighter constraints on higher-order multipole moments.

Speaker: Syed Naqvi

23 Detection prospects of parity-violating gravitational waves in third-generation ground detectors

We investigate the prospects for detecting a parity-violating gravitational-wave background with third-generation ground-based detector networks through an adapted theoretical approach combined with a data-based approach. We focus on a variety of networks consisting of an Einstein Telescope and two Cosmic Explorer detectors, varying the Einstein Telescope design, detector locations, orientations, and arm lengths to assess the impact of geometry and scale on detection capabilities. We show that the modified theoretical approach is an excellent proxy for parity violation detection and matches more robust data analysis strategies. We demonstrate that networks with an L-shaped Einstein Telescope design have stronger parity violation constraining power than networks with a triangular Einstein Telescope design, particularly seen when studying Einstein Telescope designs on their own. Our results underscore the critical role of detector configuration in probing parity violation in a gravitational-wave background.

Speaker: Hannah Duval

24 Multi-probe Cosmology with Standard Sirens: a GWxHI Cross-correlation Approach

Multi-probe techniques have proven to be powerful tools in modern cosmology.
By breaking degeneracies, they provide new ways to gain insights into the large-scale structure (LSS) of the Universe and its evolution.

In this talk, we explore the potential of cross-correlation between gravitational waves (GWs) and 21 cm intensity mapping from neutral hydrogen emission (HI), focusing on its role in view of future high-precision observatories, specifically Einstein Telescope (ET) and the Square Kilometer Array Observatory (SKAO).

Assuming that GW and HI are different tracers of the same underlying dark matter density field, we infer cosmological parameters from both the angular power spectrum (auto-correlation) and the angular cross-power spectrum (cross-correlation) of these probes.
We show that synergies between future GW and HI experiments will significantly improve standard-sirens measurements, thanks to increased sensitivity and high-redshift coverage, allowing us to constrain cosmological parameters to a level comparable to that of well-established alternative probes.

Speaker: Matteo Schulz (Gran Sasso Science Institute)

25 From Astrophysics to Cosmology: forecasting Einstein Telescope's potential with improved merger rate models for spectral siren methods

The persistence of the Hubble tension requires new validation methods. While gravitational waves provide a promising solution, the rarity of standard sirens has forced to rely on dark sirens and as such, a wealth of dark sirens methods have been developed.

In this talk we will explore our new state-of-the-art models for binary black hole (BBH) merger rates and their applications to spectral siren methods for the Einstein Telescope (ET) era.

First, we will begin with a detailed look at the astrophysical modeling and its key aspects for the evolution of the merger rate: the role of star formation history and the results from population synthesis simulations. Building on this, we will then present projected number counts and conduct a comparative analysis for different proposed design configurations for the ET.

Finally, we will showcase forecast results demonstrating the cosmological and astrophysical constraints achievable through BBH number counts alone; and then we will outline a tentative approach for a complete spectral siren method, by constructing semi-parametric mass models with redshift evolution coming naturally from our merger rate formalism.

Speaker: Giovanni Antinozzi

Site Preparation & Characterization (SCB): SCB

Conveners: Domenico D'Urso, Dr Wim Walk (Nikhef)

ECR Social Event

Wednesday 12 November

Communications

Convener: Prof. Dorota Rosinska (University of Warsaw)

Instrument Science (ISB): ISB - Contributed talks

Conveners: Jan Harms, Stefan Hild

Observational Science (OSB): OSB + EIB

Conveners: Archisman Ghosh (Universiteit Gent), Marica Branchesi, Michele Maggiore

Coffee

Communications

Convener: Prof. Dorota Rosinska (University of Warsaw)

ET e-Infrastructure Board (EIB)

Conveners: Patrice Verdier (IP2I Lyon - IN2P3), Stefano Bagnasco

Instrument Science (ISB): ISB - business

Conveners: Jan Harms, Stefan Hild

Observational Science (OSB): Div 3, 4, 7 contributions

26 Population Properties of Binary Black Holes from Star Clusters and Active Galactic Nuclei

Disentangling the astrophysical origins of gravitational waves requires confronting population properties of observed source catalogs with theoretical predictions. We investigate the formation of merging binary black holes in two distinct environments: stellar clusters and active galactic nuclei (AGNs). In clusters, repeated three-body interactions determine the dynamical assembly of binaries. Using binary population synthesis combined with post-Newtonian N-body simulations, we quantify the occurrence of highly eccentric mergers in the LVK and Einstein Telescope bands, identifying them as potential diagnostics of the cluster channel. In AGNs, we model the migration of stellar-mass black holes embedded in gaseous disks. We map the regions of parameter space where single–single encounters can occur, leading to binary formation, versus regimes where black hole pairs are trapped in mean-motion resonances, suppressing binary assembly.

Speaker: Alessandro Trani

27 Recent results on the high-energy emission from GRB jets

The detection of gravitational waves associated with short GRBs and
observations of the TeV photons from very energetic events were the
main breakthroughs in the gamma-ray burst field in past few years. I will
discuss the recent multi-wavelength observations and theoretical progress
in modelling of prompt GRB emission, including the lepto-hadronic emission
model and the model for VHE gamma-rays from a structured jet, similar to
GW170817/GRB 170817A when viewed off-axis.

Speaker: Prof. Zeljka Bosnjak (FER)

28 Gravitational wave properties of the HESS J1731-347 Object as a Twin Compact Star

In this work we present the properties of gravitational waves emitted from the f-mode oscillation of a compact star corresponding to the Object HESS J1731-347 as a Twin Compact Star, a hybrid neutron star with the same mass as a larger, purely hadronic neutron star. HESS J1731-347 is a peculiar object due to its reported compactness consisting of a mass of 0.77 solar masses and a radius of 10.4 km. Gravitational waves carry information of the damping time of the f-mode and are thought to be associated with pulsar glitches, thus providing the possibility of an upcoming multi-messenger observation performed by future gravitational waves observatories like the Einstein Telescope or the Cosmic Explorer.

Speaker: Dr David Alvarez Castillo (Institute of Nuclear Physics Polish Academy of Sciences)

29 An incremental approach for all-sky searches for continuous gravitational wave signals

All-sky searches for continuous gravitational wave signals, like those expected from asymmetric rotating neutron stars, require to analyse long stretches of data in order to increase the signal-to-noise ratio.
Typically, the heavy processing part starts after all the data to be analysed have been collected. Such a strategy is sub-optimal from a computational perspective and can significantly delay in the dissemination of results. This will be a very relevant problem for third generation detectors, like ET, due to the expected long data taking periods and the anticipated large overall computing cost of the analyses.
Analysing the data as long as they are produced, on the other hand, is not feasible without a careful algorithmic design, due to the huge amount of disk space it would be needed to store the intermediate products.
In this talk we introduce a promising implementation of an incremental search (based on the Frequency-Hough transform pipeline), which allows us to pile up the analysis intermediate products with a reasonable storage burden, and with a very small or null sensitivity loss with respect to the standard non-incremental approach. This allows to better distribute the available computing power making the analysis faster, more robust with respect to possible temporary shortages of computing resources or malfunctions of relevant services and, possibly, opening the way toward more sensitive searches.

Speaker: Cristiano Palomba

30 Probing increasingly younger neutron stars through continuous gravitational waves with higher-order spin-down parameters.

Wide-band searches for continuous gravitational waves are essential to reveal unknown neutron stars without an electromagnetic counterpart. Such searches, however, cover a huge parameter space that makes them computationally bounded. Neutron stars are predicted to slow down their rotation by losing energy through a variety of physical mechanisms, including, e.g, electromagnetic and gravitational-wave emission. The simplest possible model describes neutron stars slowing down at a constant rate by a first-order spin-down parameter that, for one-year long observing runs, is expected by neutron stars thousands or more years old. In this talk I will show that, to exploit the improved sentitivity of Einstein Telescope at low frequencies and the many-years long runs, there is the need to enlarge the parameter space to higher-order spin-down terms. I will show that in this way we can broaden the search to younger neutron stars, up to hundreds of years old or less, and discuss a possible implementation of a search including this extended model.

Speaker: Lorenzo Pierini (Istituto Nazionale di Fisica Nucleare)

Lunch

Forum of National Representatives

Convener: Michele Punturo (INFN)

Instrument Science (ISB): ISB + ETO

Conveners: Jan Harms, Stefan Hild

Observational Science (OSB): Div 10 contributions

Conveners: Archisman Ghosh (Universiteit Gent), Marica Branchesi, Michele Maggiore

31 Test of a deep anomaly detection algorithm using MDC1

We present the implementation, testing, and results of an anomaly detection pipeline based on convolutional autoencoders. After testing on white noise, we proceed to a test using MDC 1 focusing on mergers involving IMBHs and provide the results.

Speaker: Dr Huw Haigh (MBI Vienna)

32 Fast and accurate parameter estimation of high-redshift sources with the Einstein Telescope

The Einstein Telescope (ET), along with other next-generation gravitational wave (GW) detectors, will be a key instrument for detecting GWs in the coming decades. However, analyzing the data and estimating source parameters will be challenging, especially given the large number of expected detections – of order $10^5$ per year – which makes current methods based on stochastic sampling impractical. In this work, we use Dingo-IS to perform Neural Posterior Estimation (NPE) of high-redshift events detectable with ET. NPE is a likelihood-free inference technique that leverages normalizing flows to approximate posterior distributions. After training, inference is fast, requiring only a few minutes per source, and accurate, as corrected through importance sampling and validated against standard Bayesian inference methods. To confirm previous findings on the ability to estimate parameters for high-redshift sources with ET, we compare NPE results with predictions from the Fisher information matrix (FIM) approximation. We find that NPE correctly recovers the eight degenerate sky modes induced by the triangular detector geometry, which are missed by the FIM analysis, resulting in an underestimation of sky localization uncertainties for most sources. FIM also overestimates the uncertainty in luminosity distance by a factor of $\sim 3$ on average when the injected luminosity distance is $d^{\mathrm{inj}}_{\mathrm{L}} > 10^5$ Mpc, further confirming that ET will be particularly well suited for studying the early Universe.

Speaker: Filippo Santoliquido

33 Hierarchical Subtraction with Neural Density Estimators as a General Solution to Overlapping Gravitational Wave Signals

Overlapping gravitational wave (GW) signals are expected in the third-generation (3G) GW detectors, leading to one of the major challenges in GW data analysis. Inference of overlapping GW sources is complicated - it has been reported that hierarchical inference with signal subtraction may amplify errors, while joint estimation, though more accurate, is computationally expensive. However, in this work, we show that hierarchical subtraction can achieve accurate results with a sufficient number of iterations, and on the other hand, neural density estimators, being able to generate posterior samples rapidly, make it possible to perform signal subtraction and inference repeatedly. We further develop likelihood-based resampling to accelerate the convergence of the iterative subtraction. Our method provides fast and accurate inference for overlapping GW signals and is highly adaptable to various source types and time separations, offering a potential general solution for overlapping GW signal analysis.

Speaker: Qian Hu

34 Fast glitch removal method

We describe a fast glitch removal method based on the continuous wavelet transform. We give a full statistical characterization of the method and illustrate it with practical examples based on publicly available LVK data.

Speaker: Edoardo Milotti (University of Trieste and INFN-Sezione di Trieste)

35 Overlapping signals in next-generation gravitational wave observatories: A recipe for selecting the best parameter estimation technique

Third-generation gravitational wave detectors such as Einstein Telescope and Cosmic Explorer will have significantly better sensitivities than current detectors, as well as a wider frequency bandwidth. This will increase the number and duration of the observed signals, leading to many signals overlapping in time. If not adequately accounted for, this can lead to biases in parameter estimation. Our recent work combines the joint parameter estimation method with relative binning to handle full parameter inference on overlapping signals from binary black holes, including precession effects and higher-order mode content [1]. As the joint parameter estimation is computationally more expensive than traditional single-signal parameter estimation, it is crucial to devise a method to determine which method suits the problem at hand, i.e., when joint parameter estimation is necessary and when traditional single-signal parameter estimation is sufficient when analysing two overlapping signals. In an initial step, we test a time-frequency overlap method and a prior-informed Fisher matrix to help us decide when joint parameter estimation is necessary. We find the former method to be accurate in 86% of close binary black hole mergers. We improve upon previous Fisher matrix implementations by including the prior information and performing an optimization routine to better locate the maximum likelihood point point, but we still find the method unreliable. We end by developing our own method of estimating bias due overlaps, where we reweight the single signal parameter estimation posterior to quantify how much the overlapping signals affect it. We show it has 99% accuracy for zero noise injections (98% in Gaussian noise), at the cost of one additional standard sampling run when joint parameter estimation proves to be necessary.

1. T. Baka et al., “Overlapping signals in next-generation gravitational wave observatories: A recipe for selecting the best parameter estimation technique,” Phys. Rev. D. (2025), arXiv:2507.10304 [gr-qc].

Speaker: Harsh Narola

36 Bayesian Calibration of Gravitational-Wave Detectors Using Null Streams Without Waveform Assumptions

Gravitational-wave (GW) astronomy has revolutionized our understanding of the universe, but the precision of its discoveries hinges on the accurate calibration of GW detectors. In this talk, we present a novel Bayesian null-stream method for self-calibration of closed-geometry GW detector networks, such as the Einstein Telescope (ET) and LISA. Unlike traditional approaches that rely on electromagnetic counterparts or waveform models, our method leverages sky-independent null streams to constrain calibration errors using GW signals alone, independent of general relativity or waveform assumptions. We demonstrate the feasibility of this approach through proof-of-concept studies, showing that calibration constraints improve linearly with increasing signal-to-noise ratio and the presence of multiple overlapping signals. This method has the potential to enable robust parameter estimation, early-warning alerts, and cosmological studies, particularly for next-generation detectors.

Speaker: Chun-Fung Wong (KU Leuven)

37 Fast likelihood evaluation of eccentric–precessing binaries using relative binning

As gravitational-wave detectors gain sensitivity at low frequencies, inferring source properties becomes challenging due to long-duration signals and high signal-to-noise ratios. With enhanced low-frequency sensitivity, we also expect to observe many more eccentric binaries, with potentially a large impact on our understanding of binaries. The presence of orbital eccentricity enhances the emission of GW radiation not only at twice the orbital frequency but also across a whole spectrum of integer multiples of the orbital frequency. Consequently, eccentric waveforms are complex and computationally expensive, with both effects increasing with eccentricity.

We present an efficient scheme for likelihood evaluation of eccentric–precessing signals using the relative binning method. Our approach constructs the relative binning approximation mode by mode, enabling accurate incorporation of higher harmonics enhanced in eccentric systems. We apply this method to low-mass binaries with lower cutoff frequencies of 20 Hz and 5 Hz, relevant to current and future detectors. For second-generation detectors, our method achieves speed-ups of a factor of 5–20 compared to standard frequency-domain calculations. For Einstein Telescope, the computational gain is more dramatic, with likelihood evaluations accelerated by a factor of 50–1000, while maintaining accuracy. Finally, we demonstrate that posterior distributions inferred with our method are statistically indistinguishable from those obtained with exact likelihood evaluations.

Speaker: Dr Soumen Roy (UCLouvain / Royal Observatory Belgium)

Site Preparation & Characterization (SCB)

Conveners: Domenico D'Urso, Dr Wim Walk (Nikhef)

Poster Session

Conveners: Andrew Spencer, Anna Green (Nikhef), Jessica Steinlechner

Thursday 13 November

EB meeting

Convener: Michele Punturo (INFN)

Plenary: Plenary 3: ET Framework

Plenary 1: Welcome and ET Collaboration Overview

Convener: Michele Punturo (INFN)

38 The ET BGR

Speakers: Louis Smoor, Roberto Cimino

39 SiSe

Speaker: Andrew Harrison

40 Communications

41 Research and development of crystalline suspensions for ET-LF

The Einstein Telescope will utilise cryogenic cooling in the low-frequency detector, and will therefore require crystalline materials in the suspension and optical components. The material properties of these suspension materials should not limit the thermal noise performance, requiring low mechanical loss, high thermal conductivity, and suitable tensile strength. With this, there is an increasing need for novel techniques in suspension fibre fabrication and jointing. The two main material candidates are sapphire and silicon, both of which have promising cryogenic properties, but require detailed characterisation to inform realistic thermal noise models. We report recent developments from the suspensions division in fibre production and jointing methods, and updated experimental characterisation results with the aim of producing realistic thermal noise curves for both sapphire and silicon suspensions.

Speaker: Jennifer Docherty

Coffee

Plenary: Plenary 4: ETO

Plenary 1: Welcome and ET Collaboration Overview

Lunch

Social Activity: Social activity + dinner

Social Activity + Dinner:
NOTE: Transport is from the conference location to the social activity, and from there directly to dinner. If you want to participate in the dinner, but not in the social activity, you have to organize your own transport.

Friday 14 November

CB meeting

Convener: Eugenio Coccia

Plenary: Plenary 5: ET Collaboration activitie & National host teams

Plenary 1: Welcome and ET Collaboration Overview

42 SCB common activities

Speakers: Domenico D'Urso, Dr Wim Walk (Nikhef)

43 Sites - EMR

44 Sites - Lusatia

45 Sites - Sardinia

Speaker: Giovanni Bisoffi

Coffee

Plenary: Plenary 6: ET Collaboration Activities & Conclusions

Plenary 1: Welcome and ET Collaboration Overview

Conveners: Harald Lueck, Michele Punturo (INFN)

46 EIB Plenary

Speakers: Patrice Verdier (IP2I Lyon - IN2P3), Stefano Bagnasco

47 OSB Plenary

Speakers: Archisman Ghosh (Universiteit Gent), Marica Branchesi, Michele Maggiore

48 ISB Plenary

Speakers: Jan Harms, Stefan Hild

49 Announcement of Poster Prize Winners

50 Conclusions