# 11th Iberian Gravitational Waves Meeting

## Scientific Program

Invited talks are 40+5 minutes long and contributed talks 17+3 minutes long.

Click on titles of talks to see the abstracts.

Wednesday June 9
8:50 - 9:00 Opening
09:00 - 9:45 Helvi Witek [pdf]
The adventures of black holes: the case of fundamental physics
With the advent of gravitational wave astronomy we are now in a perfect position to investigate open questions in fundamental physics that range from the nature of dark matter to the nature of gravity itself. A necessary ingredient to connect advances in theoretical understanding with observations are theoretical predictions of the (gravitational) radiation emitted by compact binaries in extensions of general relativity or our standard model of particle physics. In the talk I will give an overview of recent advances in modelling black hole binaries in quadratic gravity, a quantum gravity inspired extension of general relativity, and new effects of dynamical black hole (de-)scalarization, as well as the black holes' interplay with ultralight scalars that are prominent dark matter candidates.
09:45 - 10:05 Cláudio Gomes [pdf]
Gravitational Waves in Non-Minimal Matter-Curvature Coupling Theories
Gravitational wave solutions in alternative metric theories of gravity may present up to six polarisation states. When matter is included, some additional features arise. Hence, in the context of non-minimal matter-curvature coupling theories these issues need to be addressed. We shall present the results of such analysis, both from the usual linearisation process and from the Newman-Penrose formalism. Some comments on different gravity models will be presented.
10:05 - 10:25 Christos Karathanasis [pdf]
Estimating cosmological parameters and testing general relativity using LIGO/Virgo data.
Gravitational waves detectors offer a new way of observing the universe. With the first detection of a gravitational waves event, the era of multi-messenger astronomy started. Gravitational waves events are standard candles, since the luminosity distance is directly embedded in the detected signal. This enables us to perform analyses and estimate cosmological parameters, as well as, test theories beyond general relativity . In this talk I will present estimations of cosmological and beyond general relativity parameters using LIGO/Virgo gravitational waves data.
10:25 - 10:45 Samson Leong [pdf] [key]
Refining the Hubble constant to percent level with subdominant gravitational-wave modes
The detection of the binary neutron star merger GW170817 in both the electromagnetic and gravitational channels opened the window for multi-messenger astronomy and provided an independent way to estimate the Hubble constant, albeit with O(10)% uncertainties. In the future, 2.5 and 3rd generation detectors are expected to detect at least 80 binary neutron stars per year, greatly enhancing the precision of Hubble constant estimates via combined observations. Such measurements, however, are limited by our current ability to estimate the source distance, which is degenerated with its inclination. In this talk, I will show how that the inclusion of high-order modes (emitted through both the inspiral and post-merger stages) in gravitational waves measurements of binary neutron stars mergers can break this degeneracy, improving estimates of Hubble constant and enabling measurements to O(1)% based on individual observations. Such precision would open the gate to study anisotropies and time variations of Hubble constant.
10:45 - 11:15 Coffee break
11:15 - 12:00 Daniel Figueroa [pdf]
Probing the early universe equation of state with gravitational waves
If the equation of state after inflation becomes sufficiently stiff, w >> 1/3, the inflationary background of gravitational waves (GWs) is significantly enhanced. This makes this signal potentially accessible to GW direct detection experiments. I will discuss first how LIGO and LISA could measure this signal, probing in this way the expansion rate of the early Universe. Secondly, I will show that the very same enhancement of the GW signal leads to an inconsistency in certain inflationary scenarios, violating standard bounds on the amount of radiation tolerated in the universe. Finally, I will show that the very existence of the Standard Model Higgs can actually save the day, by simply demanding the Higgs to be non-minimally coupled to gravity.
12:00 - 12:20 Mar Bastero-Gil [pdf]
2nd order induced gravitational waves from warm inflation
In warm inflation, dissipation due to the interactions of the inflaton field to other light degrees of freedom leads naturally to the enhancement of the primordial spectrum during the last 10-20 efolds of inflation. Those large fluctuations on re-entry will form light, evaporating PBHs, with masses lighter than $10^6$ g. But at the same time will act as a source for the tensors at second order. The enhancement is maximal near the end of inflation, which result in a spectral density of GW today peaked at frequencies f~ $O(10^5)$ Hz, but with an amplitude $\Omega_GW ~ 10^{-8}$. Although the frequency range is outside of present and near future GW detectors, it might be reach in future next-generation detectors, designed to detect cosmological stochastic GW backgrounds.
12:20 - 12:40 Javier Olmedo [pdf]
Anisotropic inflationary loop quantum cosmology: primordial gravitational waves and predictions for the CMB
The paradigm of slow-roll inflation provides a picture of the early universe that is in good agreement with present observations. Despite its success, most of the models studied so far rely heavily on the assumption that the universe is perfectly isotropic at early times. In this talk, I will discuss recent advances about anisotropic inflationary models, which have a well-defined dynamics at Planck scales, like in loop quantum cosmology scenarios. Here, gauge-invariant perturbations are Fock quantized and evolved through an anisotropic bounce. Despite anisotropies die out very rapidly just before the inflationary expansion, scalar and tensor perturbations keep memory of that anisotropic phase, and leave anomalies in the Cosmic Microwave Background (CMB). With these imprints and current data, we constrain the departure from spatial isotropy of the early universe, as well as discuss modifications in the usual angular correlation functions and the generation of TB and EB correlations that are forbidden in the standard isotropic scenario.
12:40 - 13:00 Alba Romero-Rodríguez [pdf]
Implications for first-order cosmological phase transitions and the formation of primordial black holes from the third LIGO-Virgo observing run
We place constraints on the normalised energy density in gravitational waves from first-order strong phase transitions and then from the formation of primordial black holes using data from Advanced LIGO and Virgo's first, second and third observing runs. First, adopting a broken power law model, we place 95 % confidence level upper limits simultaneously on the gravitational-wave energy density at 25 Hz from unresolved compact binary mergers and strong first-order phase transitions. We then consider two more complex phenomenological models, limiting at 25 Hz the gravitational-wave background due to bubble collisions and the background due to sound waves at 95 % confidence level for phase transitions occurring at temperatures above 1e8 GeV. We then do a similar search assuming a background sourced by the formation of primordial black holes and unresolved compact binary mergers. For a very generic spectrum describing the primordial black hole background, we place 95% confidence level upper limits on the gravitational-wave energy density at 25 Hz.
13:00 - 14:30 Lunch break
14:30 - 15:15 Nikolaos Karnesis [pdf]
Detecting Gravitational Waves in Space: Searching for noisy signals
In recent years we have witnessed the generation of the first catalogues of Gravitational Wave events coming from ground based detectors. The community is now developing new detectors with the aim of probing sources in the lower part of the Gravitational Wave spectrum. The ESA Laser Interferometer Space Antenna (LISA) is a space born Gravitational-Wave observatory scheduled to be launched in the early 2030s. LISA is comprised by a constellation of three satellites forming a triangle with sides of 2.5 million kilometres, following a heliocentric orbit. LISA, in contrast to present detectors, will be a signal-dominated observatory. This means that we will need to develop analysis strategies that will allow us to disentangle the signals of the various Gravitational Wave sources. In this talk I will present the LISA mission data analysis challenges, focusing on characterizing signals of stochastic nature, both from astrophysical and cosmological origin.
15:15 - 15:35 Ivan Martin Vilchez [pdf]
The LISA Data Challenges
The LISA mission needs to have a well-established ground segment. In order to put current data analysis algorithms to the test, and incentivize the creation of new ones, the LISA Data Challenges have been taking place since 2019. In this talk I will explain what they consist of, their current status, what our group's activity has been, and what we are looking to do in the future.
15:35 - 15:55 Srija Chakraborty
Probing high redshift massive blackholes with LISA
We study hydrodynamical simulations of galaxy formation, based on the GADGET-3 code, and investigate supermassive black hole binaries coalescence at $5.5 \lt z \lt 14$ and the expected gravitational waves emitted from the binary mergers for different AGN feedback models. A fraction of the accreted rest-mass energy is radiated away by each BH. A fraction of this radiated energy is coupled to the surrounding gas as feedback energy. We consider the cases of AGNfiducial feedback where the feedback energy is thermal, as well as kinetic feedback,which includes AGNcone and AGNsphere,where in the former case the kinetic BH feedback is distributed inside bi-cone (45\textdegree half opening angle) and in latter the kinetic feedback is distributed in sphere (90\textdegree half opening angle). We further consider the case in which no AGN feedback is implemented in the simulation. We find the merger rate for the kinetic feedback of the order between 100 to 1000 mergers per year for the chirpmass range less than $10^6~M_\odot$ and for the thermal feedback model to be between 100 to 500 in the same chirp mass range. We stress the comparisons to be made between simulations of same resolution: kinetic with $R_{smooth}$= 1ckpc/h and thermal with $R_{smooth}$=0.5 ckpc/h. For each model, we estimate the expected characteristic strain of gravitational waves emitted by supermassive black hole binary mergers, the time to coalesce, and the expected number of resolved events and compare our predictions with the LISA sensitivity and resolution. We further investigate the host galaxy properties for the events detectable by LISA and make predictions of the electromagnetic counter parts expected events to be detected by other electromagnetic instruments operating along the proposed operational time of LISA and present a panoramic view of merger events through different detectors.
15:55 - 16:15 David Izquierdo-Villalba [pdf]
The massive binary black hole population across cosmic time under a semi-analytical perspective
Current and future surveys are going to shed light on the formation and evolution of massive black hole binaries. While current pulsar-timing experiments will detect a gravitational wave (GW) background signal generated by the incoherent superposition of GWs from the whole population of massive binary black holes, the forthcoming LISA experiment will likely detect singular coalescences events. In this scenario, theoretical studies are vital to provide forecasts for these experiments and to help interpreting their results within a consistent cosmological picture. In this work, we contribute to these theoretical works by presenting preliminary results about binary black hole evolution by using the state-of-the-art semianalytical model L-Galaxies. The main advantage of this model is its flexibility to be run on the dark matter merger trees of the Millennium suite of simulations whose different box sizes and dark matter mass resolution offer the capability to explore different physical processes undergone by galaxies over a wide range of scales and environments. In particular, L-Galaxies includes a proper treatment for the spin and growth evolution presented in Izquierdo-Villalba et al. 2020, generating a reliable population of massive black holes at z<4. By linking this model with some physically-motivated assumptions about the pairing and hardening phase evolution of the binary systems, we can obtain predictions about how the binary population evolves with time, what are the exact properties of their hosting galaxies and what are the current expectations for the gravitational wave background in the pulsar timing array band.
16:15 - 16:45 Coffee break
16:45 - 17:05 David Keitel [pdf]
Search for lensing signatures in the gravitational-wave observations from the first half of LIGO-Virgo's third observing run
The Advanced LIGO and Advanced Virgo detectors are now observing large numbers of gravitational-wave signals from compact binary coalescences, with 50 entries in the latest transient catalogue GWTC-2. With this rapidly growing event rate, our chances become better to detect rare astrophysical effects on these novel cosmic messengers. One such rare effect with a long and productive history in electromagnetic astronomy and great potential for the future of GW astrophysics is gravitational lensing. This presentation covers the first LIGO-Virgo collaboration search for signatures of gravitational lensing in data from O3a, the first half of the third advanced detector observing run. We study: 1) the expected rate of lensing at current detector sensitivity and the implications of a non-observation of strong lensing or a stochastic gravitational-wave background on the merger-rate density at high redshift; 2) how the interpretation of individual high-mass events would change if they were found to be lensed; 3) the possibility of multiple images due to strong lensing by galaxies or galaxy clusters; and 4) possible wave-optics effects due to point-mass microlenses. Several pairs of signals in the multiple-image analysis show similar parameters and, in this sense, are nominally consistent with the strong lensing hypothesis. However, taking into account population priors, selection effects, and the prior odds against lensing, these events do not provide sufficient evidence for lensing. Overall, we find no compelling evidence for lensing in the observed gravitational-wave signals from any of these analyses.
17:05 - 17:25 Jose Diego [pdf]
Constraining Compact Dark Matter with lensed GWs
Lensed GWs are expected to be observed in the near future. For GWs with magnification factors larger than a few tens, microlensing by stellar bodies, remnants like black holes and other exotic microlenses may result in interference of the GWs. Such interference produces a modulation as a function of GW frequency that can be observed by the GW detectors. One candidate of dark matter are primordial black holes. Their abundance can be constrained through this technique by looking for interference signals in strongly lensed GWs. I will review the interference of GWs by primordial black holes and discuss prospects of their detection.
17:25 - 17:45 Rubén Arjona [pdf]
Machine learning forecasts of the cosmic distance duality relation with strongly lensed gravitational wave events
We use simulated data points from strongly lensed gravitational wave events from the Einstein Telescope to forecast constraints on the cosmic distance duality relation which relates the luminosity and angular diameter distances. In particular, we present a methodology to make robust mocks for the duality parameter η(z) and then we use Genetic Algorithms and Gaussian Processes, two stochastic minimization and symbolic regression subclasses of machine learning methods, to perform model independent forecasts of η(z). We find that both machine learning approaches are capable of correctly recovering the underlying fiducial model and provide percent-level constraints at intermediate redshifts when applied to future Einstein Telescope data.
Thursday June 10
09:00 - 9:45 Elena Cuoco [pdf]
Machine learning for transient signal analysis in Gravitational wave data
In recent years, Machine and Deep learning techniques approaches have been introduced and tested for solving problems in astrophysics. In Gravitational Wave (GW) science many teams in the LIGO-Virgo collaboration have experimented, on simulated data or on real data of LIGO and Virgo interferometers, the power and capabilities of machine learning algorithms both for the detector noise and gravitational wave astrophysical signal characterisation. In this seminar, I will show examples of the application of Machine Learning for the detection and classification of transient signals due to noise disturbances or to GW signals from Core Collapse Supernovae or Compact Binary Coalescence signals either in simulated data or in real data. I would also briefly introduce EU project dealing with these approaches: the cost action CA17137 (g2net), which aims to create an interdisciplinary network of Machine Learning and Gravitational Waves experts.
09:45 - 10:05 Alexis Menendez-Vazquez [pdf]
Searches for Compact Binary Coalescence Events using Neural Networks in LIGO/Virgo data
We present results on the search for the coalescence of compact binary mergers using convolutional neural networks and the LIGO/Virgo data. Two-dimensional images in time and frequency are used as input, and three sets of neural networks are trained separately for low mass, high mass and asymmetric mass compact binary coalescence events. We explored neural networks trained with input information from one, two and three interferometeres, indicating that the use of information from more than one interferometers leads to an improved performance. We also explore the possibility of combining the information from the different CNNs to achieve a better discrimination. Time-shifted analysis is used to estimate the background distribution of our statistic and assign a FAR to each one of our triggers. Lastly, a scan over a large sthrech of real data is performed to understand the performance of our method and to compare it with the performance from canonical pipelines.
10:05 - 10:25 Osvaldo Freitas [pdf]
Exploring gravitational-wave detection and parameter inference using Deep Learning methods
We explore machine learning methods to detect gravitational waves (GW) from binary black hole (BBH) mergers using deep learning (DL) algorithms. The DL networks are trained with gravitational waveforms obtained from BBH mergers with component masses randomly sampled in the range from 5 to 100 solar masses and luminosity distances from 100 Mpc to, at least, 2000 Mpc. The GW signal waveforms are injected in public data from the O2 run of the Advanced LIGO and Advanced Virgo detectors, in time windows that do not coincide with those of known detected signals. We demonstrate that DL algorithms, trained with GW signal waveforms at distances of 2000 Mpc, still show high accuracy when detecting closer signals, within the ranges considered in our analysis. Moreover, by combining the results of the three-detector network in a unique RGB image, the single detector performance is improved by as much as 70 %. Furthermore, we train a regression network to perform parameter inference on BBH spectrogram data and apply this network to the events from the the GWTC-1 and GWTC-2 catalogs. Without significant optimization of our algorithms we obtain results that are mostly consistent with published results by the LIGO-Virgo Collaboration. In particular, our predictions for the chirp mass are compatible (up to $3\sigma$) with the official values for 90 % of events. From these results we conclude that the combination of computer vision techniques and deep-learning methods put forward in this work is a worthy addition to the GW astronomer’s toolbox.
10:25 - 10:45 Melissa López [pdf]
Generating glitches with Generative Adversarial Networks
The noise captured by gravitational waves (GW) interferometers is limiting their sensitivity and hampers the detection of GW signals. In this regard, the most problematic types hindering the detections are transient noises, also known as glitches, that happen a few times per observed hour and can mimic GW signals. Most of the glitches show a characteristic pattern in the time-frequency domain which allows to sort them into classes, meaning that their morphologies can be learned with a Machine Learning oriented method. To this aim, we employ Generative Adversarial Networks (GANs), a state-of-the-art Deep Learning algorithm inspired by Game Theory, to learn their underlying distribution and to generate artificial populations of glitches. With this methodology, we are presently able to generate a distribution of 1000 blip glitches with a Gravity Spy confidence of (88.3+-0.8)% at a 95% confidence level in less than 1 second. This methodology will be extended by implementing a conditional-GAN to generate several classes of glitches with a single network.
10:45 - 11:15 Coffee break
11:15 - 12:00 Nikolaos Stergioulas [pdf]
Equilibrium and Dynamics of Remnants of Binary Neutron Star Mergers
Binary neutron star mergers are a goldmine for multi-messenger astronomy. Their remnants may undergo prompt collapse, or continue emitting gravitational waves, through the excitation of nonlinear oscillations. The threshold mass to prompt collapse is described by accurate empirical relations, obtained through detailed numerical simulations. I will discuss the extension of these relations to asymmetric mergers and I will present equilibrium models with realistic rotation profiles, for which the threshold mass to collapse shows a remarkable agreement with results obtained through numerical simulations. I will also discuss our latest understanding of the gravitational wave spectrum of merger remnants, the prospects for its detection and the tight constraints that can be set on the equation of state of dense matter.
12:00 - 12:20 Xiaoyi Xie [key]
Instabilities in neutron-star postmerger remnants
Using nonlinear, fully relativistic, simulations we investigate the dynamics and gravitational-wave signature associated with instabilities in neutron star postmerger remnants. For simplified models of the remnant we establish the presence of an instability in stars with moderate T/|W|, the ratio between the kinetic and the gravitational potential energies. Detailed analysis of the density oscillation pattern reveals a local instability in the inner region of the more realistic differential rotation profile. We apply Rayleigh’s inflection theorem and Fjørtoft’s theorem to analyze the stability criteria concluding that this inner local instability originates from a shear instability close to the peak of the angular velocity profile, and that it later evolves into a fast-rotating m=2 oscillation pattern. We discuss the importance of the presence of a corotation point in the fluid, its connection with the shear instability, and comparisons to the Rossby wave and Papaloizou Pringle instabilities considered in the wider literature.
12:20 - 12:40 Raphaël Raynaud [pdf]
Gravitational wave signature of proto-neutron star convection
Gravitational waves provide a unique opportunity to better constrain the dynamics in the interior of proto-neutron stars during core collapse supernovae. Convective motions inside the proto-neutron star play an important role in determining neutron star magnetic fields. In paticular, numerical models suggest that a convective dynamo could explain magnetar formation in presence of fast rotation. Using 3D MHD simulations of proto-neutron star convective zones, we compute the gravitational wave emission from turbulent convection and study the impacts of both rotation and dynamo action. We derive physical scalings that reproduce quantitatively several aspects of the numerical results. Given the potentially long duration of the signal, we find that the typical strain and frequency range could allow its detection by current GW detectors in a nearby supernova explosion, and may be a primary target for next generation of GW detectors. In some cases, the signal may even capture the growth of a magnetic field due to dynamo action.
12:40 - 13:00 Maite Mateu-Lucena [pdf]
Re-analysis of GWCT-1 with a new generation of phenomenological waveform models
We perform parameter estimation for the ten confidently detected black hole mergers in GWTC-1, i.e. for the events found by the LIGO-Virgo collaboration during the O1 and O2 observation runs. We use the fourth generation of phenomenological waveform models, the frequency domain IMRPhenomX and the time domain IMRPhenomT families. This allows us to test both waveform model families, the effects of higher modes, improved treatments of precession, alternative priors and different sampler settings. We find that IMRPhenomT further improves the fit to the data over IMRPhenomX for the most massive event, GW170729, and in the presence of evidence for spin precession. We can confirm that for most of the events the influence of adding higher modes is small if we compare it to the GWTC-1 results, obtained with MRPhenomPv2. We also discuss the automatisation of our Bayesian inference runs, which are carried out with he parallel Bilby/dynesty implementation of the nested sampling algorithm, and the training of a machine learning model in order to predict the duration of a PE run or its number of likelihood evaluations.
13:00 - 14:30 Lunch break - 13:20 GW Quiz Lunch
14:30 - 15:15 Maria Ángeles Pérez-García [pdf]
Neutron Star Crusts and GW physics
In this contribution I will discuss about the physical relevance of low density matter phases in the crust of Neutron Stars in light of Gravitational Wave emission. Additional multimessenger input, e.g. electromagnetic emission in binary merger events involving Neutron Stars, can help complement the previous information and construct a richer picture of these objects.
15:15 - 15:35 Antoni Ramos-Buades [pdf]
IMRPhenomXE: First phenomenological waveform model for eccentric binary black holes with aligned spins
The waveform models used by the LIGO and Virgo collaborations during the third observing run, O3, to detect and estimate parameters from gravitational wave (GW) signals assumed quasicircularity of the binary prior to merger. This assumption is justified as most of the binary black hole (BBH) mergers are expected to have circularized by the time they enter the detector frequency band. Nevertheless, dynamical formation channels predict a small fraction of events which could retain non-zero orbital eccentricity. Thus, with the projected increase in sensitivity of the GW detectors in the upcoming observing run, O4, it is crucial to incorporate eccentricity effects to the current waveform models in order to accurately describe the detected signals. In this work, we present the first steps towards an accurate description of the signal of eccentric non-precessing BBHs within the phenomenological (Phenom) formalism. We incorporate eccentric corrections up to 3PN order valid for small eccentricities to the quasicircular frequency domain IMRPhenomXAS waveform model. The new eccentric model, IMRPhenomXE, reduces exactly to the accurate IMRPhenomXAS model in the quasicircular limit, as well as being faithful to a set of eccentric numerical relativity (NR) with small eccentricities. Additionally, the model benefits from analytical eccentric corrections in frequency domain, which make it highly efficient for data analysis purposes. Finally, we discuss also limitations of the model and possible extensions to larger eccentricities, spin-eccentricity effects and inclusion of higher order modes.
15:35 - 15:55 Héctor Estellés [pdf]
New twists in compact binary waveform modelling: a fast time domain model for precession
In this talk we present IMRPhenomTPHM, a new time-domain wavefom model for precessing quasi-circular binary black-hole coalescence signals. The model is constructed under the paradigm of phenomenological waveform modelling, describing precessing systems through an approximate rotation of a Numerical Relativity calibrated non-precessing multimode model, IMRPhenomTHM. The time-domain construction allows several advantages with respect to the standard Fourier-domain construction in the Phenom modelling program, including a more robust and accurate description of the merger-ringdown for precessing signals, and therefore being better suited for systematic studies of short signals from massive binary mergers. We present the main features of the model and several tests addressing its accuracy and computational efficiency, including a re-analysis of the GW190412 event.
15:55 - 16:15 Jam Sadiq [pdf]
Hybrid Wave-forms for Precessing binary black holes for LIGO data
We develop a method to construct hybrid waveforms of precessing binary black holes by combining numerical relativity waveforms with analytical models. More specifically, we use the analytical models for the slow inspiral phase and numerical relativity waveforms for the late inspiral, merger, and ring-down phases. To hybridize, we align the two waveforms in the co-precessing frame using a fixed time rotation and then find appropriate rotations and time translations that maximize the overlap of the two waveforms in a hybridization interval. We discuss the accuracy and limitations for such hybrids in the context of LIGO observations.
16:15 - 16:45 Coffee break
16:45 - 17:05 Jordi Portell [pdf]
Past, present and future contributions of ICCUB to Virgo
The Institute of Cosmos Sciences of the University of Barcelona joined the Virgo Collaboration in July 2018. Since then, it has contributed on instrumentation and electronics, software engineering and data analysis. In this talk we summarize these contributions, also including the science case being built around Virgo and the prospects for the near future. Remarkably, we will present recent advances on cWB denoising (which is being carried out in collaboration with the Valencia Virgo Group), on the development and calibration of an accurate and efficient code that produces waveforms in a broad range of parameters for binary encounters, and on a research line aiming at BBH models for globular clusters.
17:05 - 17:25 Mario Martinez [pdf]
A new Instrumented Baffle for Advanced Virgo
As part of the upgrade program, Virgo has just installed a new baffle equipped with photosensors that surrounds the end-mirror of the input mode-cleaner. This culminates more than two years of work at IFAE-Barcelona for the design and construction of a novel and innovative device to control and monitor stray light inside the experiment, a persistent source of noise in interferometers. It will serve as a demonstrator of the technology for its future implementation in the main arms of the interferometer, surrounding the test masses. The new baffle will provide valuable data for understanding the cavity and calibrating simulations that describe the propagation of light within the interferometer. The instrumented baffle is now entering a long period of commissioning and integration into Virgo's regular operations, in time to become an integral part of the new O4 observation run, currently scheduled for summer 2022. In this talk we describe the technology and we present the first results of its performance within the experiment.
17:25 - 17:45 Miquel Nofrarias [pdf]
Status of the LISA Data and Diagnostics Subsystem
LISA is the future space-borne gravitational wave detector. An ESA led mission with NASA contributions with expected launch in 2034. Based on the LISA Pathfinder experience, Spain is currently planning to support the Data and Diagnostics subsystem for LISA. The Diagnostics subsystem must allow the monitoring of small environmental perturbations with the potential to disturb the geodesic motion of test masses, which will be in free fall inside each of the three space-craft. On the other hand, the Data and Diagnostics subsystem also includes the Instrument Control Computer (ICC), a key element of the payload that centralises all the data acquired on-board and interfaces several key units as the Phasemeter or the Laser. IEEC leads the Spanish contribution to LISA as a member of the LISA Instrument Group (LIG) inside the Consortium. Different groups from the institute are developing technologies and studies that are fed into the current phase A studies, in collaboration both with ESA and the two on-going industrial studies. This includes the development of high precision temperature sensors, high-precision compact magnetometers, simulations on the future radiation monitor for LISA or interface and functional definitions for the ICC. In this contribution I will report on the current status of the LISA Data and Diagnostics subsystem which, as the rest of LISA subsystems, is undergoing the LISA phase A study.
Friday June 11
09:00 - 9:45 Paola Leaci [pdf]
Unveiling the presence of Continuous Gravitational Waves in the Advanced Detector Era
Continuous gravitational Waves (CWs) are a very promising, not yet detected, and interesting class of persistent and semi-periodic signals. They are emitted mainly by rapidly rotating asymmetric Neutron Stars (NSs), with frequencies that are well covered by the [10-3000] Hz range of the Advanced LIGO-Virgo detectors. Due to the expected small degree of asymmetry of a NS, the search for this kind of signals is extremely challenging, and can be very computationally expensive when the source parameters are not known or not well constrained. CW detection from a spinning NS will allow us to characterize its structure and properties, making this source an unparalleled laboratory for studying several key issues in fundamental physics and relativistic astrophysics, in conditions that cannot be reproduced on Earth. The most recent methodologies used in CW searches will be discussed, and the latest results from the third advanced LIGO-Virgo observational run will be presented. A summary of future prospects to feasibly detect such feeble signals as the detector performance improves, and ever-more-sensitive and robust data-analysis algorithms are implemented, will be also outlined.
09:45 - 10:05 Ornella Juliana Piccinni [pdf]
Looking for neutron stars as CW-emitters in the Galactic Centre using LIGO/Virgo O3 data
We present a spotlight search for Continuous-Wave signals emitted by isolated neutron stars located in the inner parsecs of the Galactic Center. Among other options, the presence of a large population of neutron stars in this region could explain the high energy emission detected by gamma-ray telescopes like Fermi-LAT or H.E.S.S. In this work, we want to probe this possibility by looking for the gravitational wave emission from isolated neutron stars in the last observing run (O3) of Advanced LIGO and Advanced Virgo. Search methods and perspectives will be discussed.
10:05 - 10:25 Rodrigo Tenorio [pdf]
Application of a hierarchical MCMC follow-up to Advanced LIGO continuous gravitational-wave candidates
Searches for continuous gravitational waves from unknown sources generally produce a significant number of outliers. Existing follow-up methods to confirm or exclude these as viable candidates are usually limited to a particular search pipeline and require extensive calibration. We present the first application of a general-purpose hierarchical Markov chain Monte Carlo (MCMC) follow-up on continuous gravitational-wave candidates from real-data searches. Thefollow-up uses an MCMC sampler to draw parameter-space points following the F-statistic. As outliers are narrowed down, coherence time increases, imposing more restrictive phase evolution templates. This method is simpler to set up than current grid-based approaches. We introduce a Bayes factor to compare results from different stages: The probability under the signal hypothesis is derived from first principles, while for the probability under the noise hypothesis we use extreme value theory to derive a background model. The effectiveness of our proposal is evaluated on fake Gaussian data and applied to a set of 30 outliers produced by different continuous wave searches on O2 Advanced LIGO data. The results of our analysis suggest a non-astrophysical origin of all but three outliers, which we manually ascribe to instrumental artifacts and a strong hardware injection present in the data.
10:25 - 10:45 Luana Modafferi [pdf]
Search for long-duration transient gravitational waves from glitching pulsars during LIGO-Virgo third observing run
Pulsars are spinning neutron stars which emit an electromagnetic beam. We expect pulsars to slowly decrease their rotational frequency. However, sudden increases of the rotational frequency have been observed from different pulsars. These events are called “glitches”, and they are followed by a relaxation phase with timescales from days to months. Gravitational waves (GWs) emission may follow these peculiar events. We give an overview of an analysis of GW data from the Advanced LIGO and Virgo third observing run (O3) searching for transient GW signals lasting hours to months after glitches in known pulsars during the 2019-2020 run period. The search method consists of placing a template grid in frequency-spindown space with fixed grid spacings. Then, for each point we compute the transient F-statistic which is maximized over a set of transient parameters like the duration and start time of the potential signals. A threshold on the detection statistic is then set, and we search for peaks over the parameter space for each candidate. Authors: Luana Modafferi and Joan Moragues for the LIGO Scientific Collaboration and the Virgo Collaboration
10:45 - 11:15 Coffee break
11:15 - 12:00 Josefa Becerra [pdf]
Hunting for GW counterparts and kilonovas from the Canary Islands
In this contribution we will summarize the activities in which we are involved within the IAC w.r.t. the GW electromagnetic counterpart searches as well as kilonovae hunting. We will briefly mention our involvement on the detection of the first GW electromagnetic counterpart, and the follow up programs with optical telescopes that we have been working on since then. The identification of a kilonova associated with the short GRB 160821B, thanks to the lessons learned from AT2017gfo, will be discussed.
12:00 - 12:20 Youdong Hu [pdf]
BOOTES-network and GTC follow-up searches for GWs
The Burst Optical Observer and Transient Exploring System (BOOTES) is a worldwide automatic telescope network that aims to repaid follow-up of transient and astrophysical sources in the sky. Since the LIGO/Virgo interferometer was first built, the gravitational wave (GW) signal has opened a new window to explore the Universe. During the third scientific operation of LIGO/Virgo, we used BOOTES-network and Gran Telescopio Canarias (GTC) to search optical counterparts of GW events. The BOOTES network's state and their strategies in the follow-up and results in candidates searching with GTC will be present.
12:20 - 12:40 Verónica Villa-Ortega [pdf]
Rapid Online Estimation of GW Source Redshift and Astrophysical Source Category
During the third observing run (O3) of the Advanced LIGO and Advanced Virgo detectors, dozens of candidate events have been added to our gravitational wave catalogs. A challenge of this observing run has been the rapid identification and public dissemination of compact binary coalescences (CBCs), a task carried out by low-latency searches like PyCBC Live. During the later part of O3, a method of classifying CBC sources via their probabilities of containing neutron star or black hole components was developed and introduced into PyCBC Live, in order to allow immediate followup observations by electromagnetic and neutrino observatories. This fast classification between different CBC categories uses the chirp mass recovered by the search as input, given the difficulty of measuring the mass ratio with high accuracy for lower-mass binaries. As the classification requires accurate estimates of the candidate chirp mass in the source frame, a correction for the bias caused by cosmological redshift was also applied. Results for simulated signals and for candidate events identified by PyCBC Live in the first half of O3 are presented in this work.
12:40 - 13:00 Mark Gieles [pdf]
Merger rate of black hole binaries from globular clusters
Black hole binaries formed dynamically in globular clusters are believed to be one of the main sources of gravitational waves in the Universe. Here, we use a new population synthesis code, cBHBd, to determine the redshift evolution of the merger rate density and masses of black hole binaries formed in globular clusters. We simulate ~20 million models to explore the parameter space that is relevant to real clusters and over all mass scales. We show that when uncertainties on the initial cluster mass function and half-mass radius relation are properly taken into account, they become the two dominant factors in setting the theoretical error bars on merger rates. Other model parameters (e.g., natal kicks, black hole masses, metallicity) have virtually no effect on the local merger rate density, although they affect the masses of the merging black holes. We find a merger rate at z=0 of 7.2^{+21.5}_{-5.5} Gpc^-3 yr^-1 with a redshift dependence lambda = 1.6^{+0.4}_{-0.6}. The contribution of gravitational wave captures implies that eccentric mergers from globular clusters contribute <0.4 Gpc^-3 yr^-1 to the local rate. A comparison to the merger rate reported by LIGO-Virgo based on the GWTC-2 shows that a scenario in which most of the detected black hole mergers are formed in globular clusters is consistent with current constraints, and requires initial cluster half-mass densities > 10^4 Msun/pc^3. Interestingly, higher density models also result in a better match to the inferred black hole mass distribution.
13:00 - 14:30 Lunch break - 13:30 GW Quiz Lunch (part II)
14:30 - 14:50 Manuel Arca Sedda [pdf]
Merging stellar and intermediate-mass black holes in dense clusters: implications for LIGO, LISA and the next generation of gravitational wave detectors
In this talk, I will discuss one of the dynamical channels for the formation of intermediate-mass ratio inspirals (IMRIs) triggered by the interactions between two stellar black holes (BHs) and an intermediate-mass BH (IMBH) inhabiting the centre of a dense star cluster. Using N-body models and a semi-analytic approach, we show that IMRIs formation probability attains values around 5-50%, with larger values corresponding to larger IMBH masses. IMRIs map out the stellar BH mass spectrum, thus they might be used to unravel BH populations in star clusters harboring an IMBH. After the IMRI phase, an IMBH initially nearly maximal(almost non-rotating) tends to decrease(increase) its spin. If IMBHs grow mostly via repeated IMRIs, we show that only IMBH seeds sufficiently massive (mass > 300 Msun) can grow up to >10^3 Msun in dense globular clusters. Around 1-5% of seeds forming at redshift z = 2-6 would have masses in the range 500-1500 Msun at redshift 0 and would exhibit spins <~ 0.2. We show that LISA can detect IMBHs in Milky Way globular clusters with a signal-to-noise ratio SNR=10-100, or in the Large Magellanic Cloud with an SNR=8-40. We calculate the merger rate for different detectors: LIGO (Gamma = 0.003-1.6 yr^-1), LISA (Gamma = 0.02-60 yr^-1), ET (Gamma = 1-600 yr^-1), and DECIGO (Gamma = 6-3000 yr^{-1}). Our simulations show that IMRIs' mass and spin encode crucial insights on the mechanisms that regulate IMBH formation and that the synergy among different detectors would enable us to fully unveil them.
14:50 - 15:10 Juan Calderón-Bustillo [pdf]
Towards a gravitational-wave catalogue of Proca-star mergers
The third observing run of Advanced LIGO and Virgo has finally delivered a gravitational-wave signal consistent with a compact binary merger in the intermediate-mass black-hole range, known as GW190521. This signal, however, has challenged standard analyses, all done within the “canonical” paradigm of quasi-circular merging black-hole binaries. First, it required the usage of waveform models not available when the signal was detected. Second, under such assumption, GW190521 suggests the existence of a black-hole in the pair-instability supernova gap. The barely observable pre-merger emission of GW190521, however, allows for the consideration of alternative scenarios both within and beyond the black-hole merger one. In this talk, I will present show that GW190521 is consistent with merger of two exotic horizonless compact objects known as boson (Proca)-stars. This could be the first example of a future gravitational-wave catalog of new exotic objects.
15:10 - 15:30 Marta Colleoni [pdf]
A detailed analysis of GW190521 with phenomenological waveform models
In this talk we present a re-analysis of the gravitational-wave event GW190521 with state-of-the-art phenomenological waveform models, IMRPhenomX and IMRPhenomT. GW190521 provided the first direct evidence for the existence of intermediate-mass black holes and challenged our understanding of black-hole formation channels, as either or both components might lie within the pair-instability supernova (PISN) mass gap. Given the short duration of the signal, estimation of source parameters is extremely challenging and might be especially sensitive to degeneracies in current waveform templates. We illustrate how this affects parameter estimation studies and provide updated probabilities of the component masses being in the PISN mass gap, as well of the association of the event with the potential electromagnetic counterpart ZTF19abanrhr.
15:30 - 16:15 Michele Punturo [pdf]
Einstein Telescope, the 3rd generation gravitational wave observatory
Einstein Telescope (ET) is the pan-European project aiming to the realisation of a new generation gravitational wave observatory. ET promises a gain in sensitivity from one to some orders of magnitude with respect the current advanced detectors, with a particular attention at the low frequency band, below 10Hz. In order to achieve these performances, an innovative design, based on a multi-detector and multi-interferometer approach, is needed. A challenging underground research infrastructure is currently under design. Several technologies need to be developed; among them, new lasers, new optics, new cryogenic payloads, low dissipation and low absorption optical coatings, new seismic noise filters; an intense technology development programme is currently starting. Several are the science targets identified for ET, in astrophysics, multimessenger astronomy, nuclear and fundamental physics, attracting a large and diverse scientific community in to the project. An overview of the ET project, of the technology, of the science targets and of the whole realisation process will be presented.
16:15 - 16:45 Coffee break
16:45 - 17:45 REDONGRA meeting (not public)

## Social program - GW quiz lunch

• When: Thursday 10th, 13:20 (Part II: Friday 11th, 13:30)
• Who: Young researchers (in spirit)
• How: 1) bring your own lunch, 2) Play our GW games, 3) Win a prize?