GraSP23 || GravityShapePisa 2023

24 Oct 2023, 08:00 → 27 Oct 2023, 20:00 Europe/Rome

Aula Magna - Dipartimento di Fisica (Università di Pisa - Dipartimento di Fisica)

Matteo Della Rocca (Istituto Nazionale di Fisica Nucleare)

GravityShapePisa: New Frontiers in Gravity Phenomenology

 

GravityShapePisa(GraSP) is the 2^nd International Conference completely organized by Young Researchers which supports the active participation of Young Researchers.

The event is organized so as to provide balanced alternation of "Senior" and "Young" talk sessions on the field of the observative and theoretical Physics. This will give the opportunity to early-stage researchers, severely penalized by the pandemic, to spread their work, but also to experienced scientists to be aware about original research inputs coming from younger physicists.

 

GraSP 2023 will take place in the Physics Department “E. Fermi” of the University of Pisa.

The aim of the conference is to gather theoretical and observational researches from different international groups to discuss new challenges in gravity phenomenology at different curvature scales.

The event is spread over four days. On the first two days, frontiers of black hole physics will be the main topic. During the third day, multi-messenger astrophysics and the signatures of exotic compact objects will be covered. Finally, the fourth day will focus on future experiments inside the solar system, which will allow to test General Relativity against alternative gravity theories.

The event includes talks about new techniques to model, detect and recognise gravitational waves from binary systems and exotic objects, new possible tests of General Relativity against alternative gravity theories throughout new detectors and new challenges in experimental astrophysics via Einstein Telescope.

No FEE required.

Conference e-mail

 

Organizing committee contact information:

 

Matteo Della Rocca

matteo.dellarocca@phd.unipi.it

Giuseppe Di Somma

giuseppe.disomma@phd.unipi.it

Maria Antonietta Palaia

mariaantonietta.palaia@phd.unipi.it

Lucia Papalini 

lucia.papalini@phd.unipi.it

Franceso Tarantelli

francesco.tarantelli@phd.unipi.it

Michele Vacatello 

michele.vacatello@phd.unipi.it

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Tuesday, 24 October

08:30 → 09:00 Registration

09:00 → 09:30 Welcome: Opening

09:30 → 11:00 Science with Einstein Telescope

Conveners: Giuseppe Di Somma (University of Pisa and INFN), Lucia Papalini (University of Pisa and INFN)

09:30 Einstein Telescope and the future generation of Gravitational Wave observatories.

Gravitational waves (GWs) are the newest tool for exploring the Universe. Advanced Virgo and Advanced LIGO have opened a new window on the Universe, detecting GW signals in the Hz-kHz frequency range. The Pulsar Timing Array experiments have just announced the detection of GWs in the nano-Hz frequency range.
A new generation of GW interferometric observatories is under preparation and will take over from the current generation of GW detectors in the next decade. This will make it possible to probe almost the entire Universe for GW signals. The Einstein Telescope (ET) and the Cosmic Explorer (CE) are at the forefront of the design, preparation and realisation of a next-generation gravitational wave observatory in Europe and the USA respectively. The space-based GW detector LISA will be launched in the next decade and will complete the new series of GW observatories.
With a special focus on the Einstein Telescope observatory, an overview of the scientific objectives, the observatory design, the required technologies and the project organisation will be presented.

Speaker: Michele Punturo (Istituto Nazionale di Fisica Nucleare)

ET-Punturo-GRASP2023.pptx

10:00 The Einstein Telescope, the next generation detector for Gravitational Wave observation

The detection of Gravitational Waves (GWs) opened a new window on the Universe. The combined observation of GW and electromagnetic signals from astrophysical phenomena in 2017 signed the beginning of the Multi-messenger Astronomy.
While LIGO-Virgo-KAGRA Collaborations keep on detect GWs, a new generation of GW observatories is under preparation and will take over in the next decade, allowing to probe almost the entire Universe. The Einstein Telescope (ET) is the European project for the future GW detection.
An overview of the scientific objectives, the status of detector design, its technological challenges and the expected implications to the Gravitational Wave Astronomy progress will be presented.

Speaker: Prof. Domenico D'Urso (University of Sassari and INFN-LNS)

ET_durso_grasp2023.pdf

10:30 Fundamental Physics and Cosmology with the Einstein Telescope

The observation of gravitational waves by the LIGO/Virgo collaboration has opened a new window on the Universe. In this decade, however, these experiments will reach the limit of their capabilities, and a new generation of ground-based detectors is being planned. In Europe, this has led to the proposal of the Einstein Telescope. With order of magnitude improvement in the sensitivity, Einstein Telescope will explore the depth of the Universe using gravitational waves, and has the potential of triggering revolutions in astrophysics, cosmology and fundamental physics. We will give a broad overview of its capabilities and scientific targets.

Speaker: Michele Maggiore (Geneva University)

Pisa2023.pdf

11:00 → 11:30 Coffee Break

11:30 → 13:00 Neutron Stars to test Cosmology scenarios

Conveners: Giuseppe Di Somma (University of Pisa), Lucia Papalini (University of Pisa)

11:30 Infinite-duration Continuous Gravitational Waves from neutron stars in binary systems

The gravitational-wave astronomy field has been resolutely founded seven years ago, thanks to the first direct
detection of transient gravitational waves from the collision of two black holes.
The first detection of continuous gravitational waves from fastly rotating neutron stars, either isolated or in binary systems, has yet to be done, and it may be around the corner, representing a further revolutionary big discovery.
The search for this kind of signals, which is among the most interesting targets of the Advanced LIGO-Virgo-KAGRA detectors is challenging due to their expected weakness, and can be very computationally expensive especially when the source parameters are not well constrained, and especially for sources in binary systems.
In this talk I will present the methodologies used in CW searches from neutron stars in binary systems, and recent results from the latest advanced LIGO-Virgo-KAGRA observational runs.

Speaker: Dr Paola Leaci (Sapienza University of Rome)

GraSP23_PLeaci.pdf

12:00 Non-local Gravity Cosmology

Recently the so-called Non-Local Gravity acquired a lot of interest as an effective field theory towards the full Quantum Gravity. In this talk, we sketch its main features, discussing, in particular, possible infrared effects at astrophysical and cosmological scales. In particular, we focus on general non-local actions, including curvature or torsion invariants. In all cases, characteristic lengths emerge at cosmological and astrophysical scales. Furthermore, it is possible to fix the form of the Lagrangian and to study the cosmological evolution considering the existence of Noether symmetries. We discuss also possible astrophysical and cosmological applications for non-local gravity models considering late time cosmic expansion, the structure of galaxy clusters, the S2 orbit around the Galactic Center, the possibility of further modes in gravitational waves. As a final comment it is worth saying that non-locality can be tested in various infrared regimes bringing together physics of short and large scales. Clearly, the possibility to find further gravitational wave modes could be an important test bed for the theory.

Speaker: Salvatore Capozziello (Istituto Nazionale di Fisica Nucleare)

Capozziello_NLGr_Cosmology.pdf

12:30 Gravitational wave generation in effective field theories of dark energy

I will review how non-linearities can allow for screening solar-system
scales from non-tensorial gravitational polarizations, focusing on the
case of scalar-tensor theories with derivative self-interactions
(K-essence). I will then present fully relativistic simulations in
these theories in 1+1 dimensions (stellar oscillations and collapse)
and 3+1 dimensions (binary neutron stars), showing how to avoid
breakdowns of the Cauchy problem that have affected similar attempts
in the past. I will show that screening tends to suppress the
(subdominant) dipole scalar emission in binary neutron star systems,
but that it fails to quench monopole scalar emission in gravitational
collapse, and quadrupole scalar emission in binaries

Speaker: Enrico Barausse

14:30 → 15:30 Black Holes to probe General Relativity

Conveners: Matteo Della Rocca (University of Pisa), Michele Vacatello (University of Pisa)

14:30 Black holes in effective field theories – dynamics and new observational signatures

Black holes in effective field theories, such as scalar-Gauss-Bonnet and dynamical Chern-Simons gravity, offer interesting alternatives to the Kerr solution that can be tested observationally. Interestingly, the deviations from GR can be not only quantitative but strong quantitative differences can also appear. This includes the appearance of jumps between stable branches of solutions, violation of the equatorial symmetry, etc. In the present talk, we will discuss some of the most interesting examples of such beyond-Kerr black holes. Special attention will be paid to their nonlinear dynamics and the potential problems such as loss of hyperbolicity.

Speaker: Daniela Doneva (University of Tuebingen)

Talk_Doneva.pdf

15:00 Probing scalar fields with Extreme Mass Ratio Inspirals and LISA

Extreme Mass Ratio Inspirals (EMRIs), binary systems with a secondary stellar mass compact object inspiralling into a massive black hole, are among the main targets for LISA, as they harbour the potential for precise strong gravity tests. Although the description of these systems in modified theories of gravity can be drastically complex, for a vast class of theories with additional scalar fields great simplifications occur. At leading order in the binary mass ratio, the primary scalar charge is suppressed, so that the background spacetime is simply described by the Kerr metric. Moreover, the imprint of the scalar field on the waveform is fully captured by the scalar charge carried by the secondary and by the mass of the scalar field. In this talk I will show how, using these simplifications, the secondary’s scalar charge and the scalar field mass affect the EMRI’s orbital evolution, and how such changes get imprinted on the emitted waveforms. By analysing such signals, I will finally present the results on the LISA’s detectability of the scalar charge and mass, which render EMRIs encouraging probes of new fundamental fields.

Speaker: Susanna Barsanti (Sapienza University of Rome)

15:30 → 15:45 Poster Advertisment Session

15:45 → 16:15 Coffee Break

16:15 → 18:15 Poster Session

16:15 Bounds on Ultralight Dark Matter from NANOGrav

The detection of the stochastic gravitational wave background by NANOGrav imposes constraints on the mass of compact cores of ultra-light dark matter, also known as "solitons", surrounding supermassive black holes found at the centers of large galaxies. The strong dynamical friction between the rotating black holes and the solitons competes with gravitational emission, resulting in a suppression of the characteristic strain in the nHz frequency range. Our findings robustly rule out ultralight dark matter particles with masses ranging from $1.3\times 10^{-21}$eV to $1.4\times 10^{-20}$eV condensing into solitons around supermassive black holes.

Speaker: Mohammad Aghaie Moghadam Ozbak (Istituto Nazionale di Fisica Nucleare)

16:15 Fermion soliton stars

Fermion soliton stars are a motivated model of exotic compact objects in which a nonlinear self-interacting real scalar field couples to a fermion via a Yukawa term, giving rise to an effective fermion mass that depends on the fluid properties. For the first time, we study this model within General Relativity without approximations, finding static and spherically symmetric solutions. If the scalar potential features asymmetric vacua, the mass and radius of a fermion soliton star are comparable to those of a neutron star for natural model parameters at the GeV scale. Moreover, the asymmetric scalar potential inside the star can provide either a positive or a negative effective cosmological constant in the interior, being thus reminiscent of gravastars or anti-de Sitter bubbles, respectively. Finally, we explore embedding in particle-physics contents, showing that if the fermion is strongly coupled to the scalar field, non-perturbative bound states describing false vacuum pockets are found. Possible connections with dark matter and cosmology are also briefly discussed.

Speaker: Loris Del Grosso (La Sapienza University of Rome)

16:15 Gravity and the Superposition Quantum Principle

The relation between gravity and quantum mechanics is investigated in this work. The link is given by the wave packet expansion process, rooted from the Uncertainty Principle.
The wave packet spreading is studying in spherical coordinates, whose width $\sigma(t)$ is expressed in terms of $G$ and $c$, instead of $\hbar$. Therefore, for masses larger than the Planck mass, a faster dispersion rate of $\sigma(t)$ is obtained, compared to the standard case. The dispersion of the wave packet is observed only by a free falling observer and the process stops once the observer hits the surface of the object. Different observers notice different rates of expansion of the wave packet and the source of gravity is in a quantum superposition.

Speaker: Hristu Culetu (Ovidius University)

16:15 Neutrons in the Low-Curvature Limit: post-Newtonian effects and more

Ultracold neutrons are a great tool to explore the quantum nature of the gravitational interaction. From a theoretical perspective, starting from a Dirac equation in curved spacetime, one can derive the non-relativistic Schrodinger equation that governs the evolution of the neutron's wave function in the Earth's gravitational field. At the lowest order, this procedure simply reproduce a Schrodinger system affected by a Newtonian potential. However, in this talk, we argue that one should be very careful when calculating next-to-leading order corrections, since terms that at first glance seems negligible end up playing an important role at this level. Furthermore, also the differences in the nature of physical and coordinate distances show up in the corrections to the neutron energy spectrum and they must be taken into account. Finally, we observe that, even if the current Ultracold neutrons experiments' precision does not allow to probe for these perturbations yet, they could still be relevant in the future or in other ad-hoc circumstances.

Speaker: Alessandro Santoni

16:15 Non-Gaussianity from the Cross-correlation of the Astrophysical Gravitational Wave Background and the Cosmic Microwave Background

Since the first LIGO/Virgo detection, Gravitational Waves (GWs) have been very promising as a new complementary probe to understand our Universe. One of the next challenges of GW search is the detection and characterization of the stochastic gravitational wave background (SGWB), that is expected to open a window on the very early Universe (cosmological background) and to provide us new information on astrophysical source populations (astrophysical background). In this talk, I will focus on the anisotropic contribution of such a signal, imprinted both at the production and in the propagation towards the Earth, accounting for the properties of the astrophysical sources. Specifically, I will present the cross-correlation between these anisotropies and the Cosmic Microwave Background (CMB) ones. Furthermore, I will talk about the possibility to measure non-Gaussianity (nG)
accounting for large-scale corrections to the bias and the capability of next generation space-based interferometers to detect such a cross-correlation signal.

Speaker: Gabriele Perna (Istituto Nazionale di Fisica Nucleare)

Wednesday, 25 October

09:00 → 09:30 Black Holes Astrophysics

Conveners: Francesco Tarantelli (University of Pisa), Maria Antonietta Palaia (University of Pisa)

09:00 The massive black hole binary path to coalescence

Massive black hole binaries (MBHBs) are expected to form at the centre of merging galaxies during the hierarchical assembly of the cosmic structure and are expected to be the loudest sources of gravitational waves (GWs) in the low frequency domain surveyed by the ongoing Pulsar Timing Array (PTA) campaigns and by the forthcoming LISA observatory.
A meaningful assessment of the detection prospects of the above experiments critically depends on the abundance and properties of MBHBs that form and evolve during the cosmic history. Therefore, understanding the MBH dynamical evolution before and after these binaries form is of paramount importance.
In this talk I will review the current understanding of MBHB evolution by analysing the several dynamical processes driving MBHBs at different scales and highlighting possible evolutionary bottlenecks that may arise along their path to coalescence.

Speaker: Matteo Bonetti (University of Milano-Bicocca)

The massive black hole binary path to coalescence.pdf

09:30 → 10:30 Quasi Normal Modes for Kerr Black Holes

Conveners: Francesco Tarantelli (University of Pisa), Maria Antonietta Palaia (University of Pisa)

09:30 Non-linear Black Hole Ringdowns: an Analytical Approach

Due to the nature of gravity, non-linear effects are left imprinted in the quasi-normal modes generated in the ringdown phase of the merger of two black holes. We offer an analytical treatment of the quasi-normal modes at second-order in black hole perturbation theory which takes advantage from the fact that the non-linear sources are peaked around the light ring. As a byproduct, we describe why the amplitude of the second-order mode relative to the square of the first-order amplitude depends only weakly on the initial condition of the problem.

Speaker: Davide Perrone (University of Geneva)

Grasp_NL_Perrone.pdf

10:00 Black hole spectroscopy beyond Kerr

Black-hole spectroscopy is one of the most promising tools to test gravity in extreme regimes and to probe the nature of black holes. However, tests based on ringdown observations are currently limited by the lack of parametrization that are both robust and accurate, able to capture generic modifications of the Kerr spectrum. In this talk I will present a new observable-based parametrization of the ringdown of spinning black holes beyond general relativity, ParSpec, and its application to future detections by 3G interferometers. I will discuss projected measurements on the ringdown parameters, and how to map such agnostic constraints on bounds on the fundamental couplings of
modified theories of gravity. Finally I will exploit ParSpec to discuss generic limitations of ringdown tests.

Speaker: Andrea Maselli (Istituto Nazionale di Fisica Nucleare)

10:30 → 11:15 Coffee Break

11:15 → 12:15 Gravitational Waves from Scattering Amplitudes

Conveners: Francesco Tarantelli (University of Pisa), Maria Antonietta Palaia (University of Pisa)

11:15 Gravitational observables from quantum scattering amplitudes

Since the first detection of gravitational waves, the need for precise prediction of waveform templates has pushed to develop modern approaches to compute gravitational observables. One of the most promising programs is based on treating gravity as an effective field theory and extracting classical observables from quantum scattering amplitudes. The systematic approach lies on the eikonal expansion, in which the perturbative series in the Newton constant is organized in loop amplitudes computations. While most of the efforts are focused on on-shell scattering amplitudes, seems that exploiting the Kerr-Schild gauge in an off-shell approach can lead to new theoretical insights for a better understanding of gravity, as well as phenomenological applications, as the computation of the scattering angle of an external charged probe off a Kerr-Newman black hole at every order in the angular momentum.

Speaker: Claudio Gambino (Istituto Nazionale di Fisica Nucleare)

GraSP_23.pdf

11:45 Gravitational Waves Observables From Scattering Amplitudes

The extraordinary detection of gravitational waves (GWs) emitted by binary coalescing systems gave us a new instrument to probe our Universe and to test General Relativity (GR). The increasing precision of current and future GWs interferometers requires very accurate predictions of GWs observables. Scattering amplitudes techniques, which for decades have been developed for collider experiments, are now being used to study classical two body problems in GR. I will show how GWs observables can be expressed in terms of scattering amplitudes within the KMOC approach and will highlight how they can efficiently be computed within a heavy mass framework (HEFT).

Speaker: Giacomo Brunello (UNIPD & IPhT, CEA-Saclay & INFN-PD)

Brunello_grasp23.pdf

12:15 → 12:45 Exotic Compact Objects

Conveners: Francesco Tarantelli (University of Pisa), Maria Antonietta Palaia (University of Pisa)

12:15 Tests of the nature of black holes with gravitational waves

Gravitational waves open the possibility to investigate the nature of compact objects and probe the existence of horizons in black holes. This is of particular interest given some quantum-gravity models which predict the presence of horizonless and singularity-free compact objects. Such exotic compact objects can emit a different gravitational-wave signal relative to the black hole case. In this talk, I derive the characteristic oscillation frequencies of horizonless compact objects in the ringdown. Finally, I describe how parametrised tests on general relativity can allow for tests of the black hole paradigm.

Speaker: Dr Elisa Maggio (Max Planck Institute for Gravitational Physics, Albert Einstein Institute, Potsdam)

GraSP.pdf

14:30 → 15:30 Exotic Compact Objects

Conveners: Francesco Tarantelli (University of Pisa), Gregorio Paci (University of Pisa)

14:30 Searching for continuous gravitational waves: the remainder of the zoo

While the prototypical source of continuous gravitational waves is represented by asymmetric spinning neutron stars, there are several other mechanisms which are expected to cause the emission of long-lasting semi-periodic signals which, if detected, would provide a wealth of information about several aspects of fundamental physics, astrophysics and cosmology.
They include newborn magnetars, ultra-light dark matter and sub-solar mass primordial black holes, object of a very intense research activity in the gravitational wave community.
In this talk I will briefly review these sources, discussing their emission processes, the main data analysis techniques used for their search, recent upper limits obtained by the LIGO-Virgo-Kagra Collaboration and future prospects.

Speaker: Cristiano Palomba (Istituto Nazionale di Fisica Nucleare)

palomba_Grasp2023.pdf

15:00 Searching for evidences of Exotic Compact Objects from the spin distribution of compact binary coalescences

Black holes (BHs) are among the most fascinating objects in the Universe. However, their description presents several theoretical difficulties such as the presence of a horizon at radius $r_+$. A class of horizonless objects, known as exotic compact objects (ECOs), have been formulated, in order to remove these difficulties. ECO's models generally predict the presence of a physical surface at a radius $r=r_+(1+\epsilon)$, where $\epsilon$ quantifies the scale at which General Relativity should be corrected. A quantum scale would correspond to $\epsilon < 10^{-30}$.
Differently from BHs, ECOs are subject to ergoregion instability, i.e. a process that prevents the formation of ECOs spinning above a certain critical limit $\chi_{\rm crit}$ that depends on the compactness of the object and its reflectivity. As a result, the spin distribution of a population of ECOs will display local overdensities in correspondence of $\chi_{\rm crit}$.
Gravitational waves (GWs) from Compact Binary Coalescences (CBCs) offer a powerful tool probe for the existence of ECOs. By studying the spin distribution of CBCs, it is possible to probe the existence of ECOs.
In this talk, we propose to study the spin distribution of 90 CBCs with a population model that includes the possible presence of ECOs. When assuming that the population of CBCs is entirely composed by ECOs, we are able to set a lower limit on $\epsilon \geq 10^{-5}$ thus excluding the possibility of a population of ultra-compact objects ($\epsilon < 10^{-30}$). Instead, if we assume a population of mixed BHs and ECOs, we obtain that no more than 60 % of the CBCs observed can be composed of ultra-compact objects.

Speaker: Adriano Frattale Mascioli (Sapienza, INFN)

presentazione_GraSP.pdf

presentazione_GraSP.pptx

15:30 → 16:00 Coffee Break

16:00 → 16:45 Prospects in Black Hole Physics: Discussion Session

Convener: Michele Maggiore (University of Geneva)

16:45 → 17:30 Exotic Compact Objects and Theories Beyond General Relativity: Discussion Session

Conveners: Cristiano Palomba (INFN Roma1), Daniela Doneva (University of Tübingen), Elisa Maggio (Max Planck Institute for Gravitational Physics (Albert Einstein Institute))

17:30 → 20:00 Aperi-dinner

Thursday, 26 October

09:00 → 11:00 Neutron Stars in Gravitational Wave Physics

Conveners: Maria Antonietta Palaia (University of Pisa), Michele Vacatello (University of Pisa)

09:00 20 years of testing GR with the Double Pulsar

Pulsars are extremely stable natural clocks and, when found in a relativistic binary system, they can be used as exceptional laboratories to test Relativistic gravity in the strong field regime. In this talk I will present the results obtained in this context by studying the now 20-year-long dataset on the double pulsar system J0737-3039A/B, the only binary hosting two active radio pulsars, and one of the most relativistic systems known to date. The double pulsar laboratory has indeed allowed us to confirm the validity of GR at least at 99.99% and to measure several relativistic effects for the first time.

Speaker: Marta Burgay (INAF - Osservatorio Astronomico di Cagliari)

DPSR@GRASP_Pisa2023.pdf

09:30 Testing strong-field gravity with multimessenger observations of neutron stars

Neutron stars are some of the most extreme objects in Nature. Their typical masses (around 1.4 times that of the Sun) combined with their small radii (about 12 km) result in densities exceeding the nuclear saturation density, above which exotic states of matter can form. Moreover, neutron stars are among the strongest gravitational field sources known, second only to black holes. These properties make neutron stars exceptional laboratories to study matter and gravity in extreme situations, out of reach of terrestrial and Solar System experiments. I will discuss how neutron star observations, both with the x-ray Neutron Star Interior Composition Explorer (NICER) mission and with gravitational-wave observatories (LIGO-Virgo-Kagra), offer us new avenues to test general relativity and constrain modifications thereof.

Speaker: Hector Silva

20231026_grasp.pdf

10:00 A Gravitational-Wave Perspective on Neutron Star Seismology

Neutron star seismology, which aims to probe the extreme physics associated with these objects, is of increasing relevance for gravitational-wave astronomy. Focussing on the fundamental mode of oscillation, which is an efficient gravitational-wave emitter, I will the outline the seismology aspects of a number of astrophysically relevant scenarios; ranging from the star’s birth in a core collapse through to transients (like pulsar glitches and magnetar flares), the dynamics of tides in inspiralling neutron-star binaries, the oscillations of the final merged object and instabilities that may be acting in the remnant (or, indeed, isolated rapidly rotating, neutron stars). The main aim is to introduce the key ideas and highlight issues that need further attention if we want to realize the potential of the next generation of gravitational-wave instruments.

Speaker: Prof. Nils Andersson (University of Sotuhampton)

NAseismo.pdf

10:30 RECENT RESULTS AND FUTURE CHALLENGES FOR ISOLATED SOURCES OF CONTINUOUS GRAVITATIONAL WAVE SEARCHES WITH A NETWORK OF TERRESTRIAL GRAVITATIONAL WAVE DETECTORS

Following the historic discovery of the signals from coalescing black hole and neutron star (NS) binaries, a new frontier in gravitational wave (GW) research is the detection of sources emitting periodic continuous waves (CWs).
Fast rotating NSs, emit a nearly monochromatic CW signal, whose frequency is proportional to the spin frequency.

An electromagnetic (EM) counterpart of CWs is expected, but EM-silent NSs are also potential CW sources.
The detection of GWs from these sources is a high priority task for the LIGO/Virgo/KAGRA collaborations. The most recent efforts and results, together with future challenges, concentrating on the search for isolated neutron stars, will be presented in this talk.

Speaker: Pia Astone (Istituto Nazionale di Fisica Nucleare)

PiaAstonePISA2023.pptx

RECENT RESULTS AND FUTURE CHALLENGES FOR ISOLATED CONTINUOUS GRAVITATIONAL WAVE SEARCHES WITH A NETWORK OF TERRESTRIAL GRAVITATIONAL WAVE DETECTORS

11:00 → 11:30 Coffee Break

11:30 → 13:00 Machine Learning for Gravitational Waves

Conveners: Maria Antonietta Palaia (University of Pisa), Michele Vacatello (University of Pisa)

11:30 Gravitational Wave Searches, Public Alerts, and Event Validation in the Fourth Observing Run of LIGO, Virgo and KAGRA

The first three observational campaigns of the Advanced LIGO and Advanced Virgo gravitational-wave (GW) detectors have culminated in the confident identification of 90 signals arising from the mergers of compact binary systems composed of black holes and neutron stars. These events have offered a new testing ground for General Relativity and better insights into the nuclear equation of state for neutron stars, as well as the discovery of a new population of black holes.
In the ongoing fourth joint observing run by the LIGO, Virgo, and KAGRA collaborations (collectively referred to as LVK), substantial improvements have been implemented to enhance the detectors' sensitivity. These enhancements are poised to significantly boost the rate of detections, promising new discoveries and more profound insights into the aforementioned domains. To support these goals, substantial progress has been made in fortifying the low-latency infrastructure to foster multimessenger searches. The operations of rapid response to GW candidate alerts and event validation procedures as been refined as well to strengthen the confidence in the detected signals.
This presentation offers an overview of the upgrades made to the detectors from O3 to O4 and the expected increase in event detection rates. Furthermore, it delves into the key aspects of GW transient searches, encompassing the dissemination of public alerts and the meticulous validation of candidate events, including the noise artifact mitigation before parameter estimation analyses, and the inclusion of the events in discovery papers or catalogs.

Speaker: Francesco Di Renzo

12:00 Neural network time-series classifiers for gravitational-wave searches in single-detector periods

The search for gravitational wave signals in the data collected by the current ground-based interferometers is a complex problem, especially when only one detector operates. Modern deep learning approaches could contribute to find a solution. I'll discuss the detection problem and present the work detailed in arXiv:2307.09268 where we investigate the performance of neural network classifiers based on three types of architectures: convolutional neural network, temporal convolutional network, and inception time. The last two architectures are specifically designed to process time-series data. We apply the trained classifiers to LIGO data from the O1 science run, focusing specifically on single-detector times. We find a promising candidate on 2016-01-04 12:24:17 UTC compatible with a black hole merger with masses 50 M⊙ and 24 M⊙.

Speaker: Agata Trovato (Istituto Nazionale di Fisica Nucleare)

Trovato_GraSP23.pdf

12:30 Machine Learning for Transient signal analysis in Gravitational Wave data

The application of Machine and Deep learning techniques in astrophysics has gained significant attention also within the field of Gravitational Wave (GW) science, where numerous teams in the LIGO-Virgo collaboration have been exploring the potential of machine learning algorithms. These algorithms have been tested using both simulated and real data from LIGO and Virgo interferometers, focusing on tasks such as noise reduction and characterizing astrophysical signals.

I will provide specific examples demonstrating the effectiveness of Machine Learning in identifying and classifying transient signals arising from noise disturbances or GW events, including Core Collapse Supernovae and Compact Binary Coalescence events.

Speaker: Elena Cuoco (EGO & SNS)

Grasp2023-Cuoco.pdf

14:30 → 15:30 Neutron Stars: Matter at the Extremes

Conveners: Gregorio Paci (University of Pisa), Matteo Della Rocca (University of Pisa)

14:30 The neutron star matter Equation of State: a challenge for nuclear physics theory

I will review the recent developments in the construction of the Equation of State of hot and dense matter and its application to neutron stars observations, which have become recently a fundamental tool to constrain the properties of nuclear matter. I will discuss the main open questions in the nuclear many-body theory and its future perspectives.

Speaker: Dr Fiorella Burgio (INFN Sezione di Catania)

Talk_GraSP.pdf

15:00 Pions, hyperons and quark matter in neutron star mergers

We discuss recent calculations investigating the detailed impact of various "non-nucleonic" degrees of freedom in neutron star mergers. Pions are neglected in equation of state tables for merger simualtions but might actually occur in neutron star matter. We quantify their potential impact on the obseravbles of neutron star mergers. We describe a weak but potentially measurable signature of hyperons on neutron star mergers. Finally, we discuss the effects of deconfined quark matter.

Speaker: Dr Andreas Bauswein (GSI Darmstadt)

talk_Pisa.pdf

15:30 → 15:45 Poster Advertisment Session

15:45 → 16:15 Coffee Break

16:15 → 17:00 Prospects in Neutron Stars Physics: Discussion Session

Conveners: Fiorella Burgio (INFN Catania), Pia Astone (INFN Roma1)

17:00 → 19:00 Poster Session

17:00 A resampling search method for sub-solar mass binary inspirals

Primordial black holes are proposed to have formed in the very early universe and a first detection of them would provide valuable insights into cosmology, dark matter, and physics of the very early universe. Primordial black holes could form binaries systems with chirp masses of the order of $\mathcal{O}(10^{-5})M_\odot - \mathcal{O}(10^{-3})M_\odot$, which would emit long transient gravitational waves signals that last of the orders of hours - years. We present an implementation of a resampling algorithm to search for such signals in gravitational wave data. An estimate for the distance sensitivity of the technique suggests that the Galactic Centre can be probed for large portions of the parameter space studied. We also present preliminary results about efficiently construct a search grid and the expected computational cost of a directed search towards the Galactic Centre.

Speaker: Neil Lu (Australian National University)

17:00 Binary black hole mergers from Population III stars

In this presentation, I will provide a comprehensive analysis of the uncertainty regarding the merger rate density and mass spectrum of binary black holes (BBHs) originating from Population III (Pop. III) stars. I will explore four distinct formation histories of Pop. III stars and investigate 11 models concerning the initial orbital properties of their binary systems.

The results I have obtained demonstrate a significant impact of uncertainties of the orbital properties on the BBH merger rate density, potentially varying up to two orders of magnitude. Specifically, models with shorter initial orbital periods tend to lead to higher merger rates. Additionally, the uncertainty in the star formation history significantly influences both the shape and normalisation of the BBH merger rate density. Depending on the assumed star formation rate, the peak of the merger rate density can shift from $z \sim 8$ to $z \sim 16$. Moreover, the maximum BBH merger rate density for our fiducial model ranges from $ \sim 2$ to $\sim 30$ Gpc$^{−3}$ yr$^{−1}$.

I find that the typical BBH masses are not affected by the star formation rate model and only mildly influenced by the binary population parameters. Pop. III primary black holes are generally more massive, ranging from 30 to 40 M$_\odot$, compared to those formed from metal-rich stars (8 - 10 M$_\odot$).

Finally, I estimate that the Einstein Telescope will detect 10 − 10$^4$ Pop. III BBH mergers per year, depending on the star formation history and binary star properties.

Speaker: Filippo Santoliquido (Istituto Nazionale di Fisica Nucleare)

17:00 Binary neutron star mergers in massive scalar-tensor theory: an adiabatic look

In massive scalar-tenor theories, a Compton length-scale will be introduced by the scalar mass. In the context of binary systems, the influences of such length-scale include the suppressions in the scalar interaction between the two members when the orbital separation well exceeds the scale, and in the emissivity of scalar radiation with wavelength longer than that. We focus here on coalescing binary neutron stars, where we investigate the scalar effect on the late-inspiral dynamics. It has been found that the scalar activity becomes dynamically important only when the orbital separation shrinks within a few times of the Compton length-scale. Therefore, certain constraints may be placed on the theory by scrutinising the late-inspiral waveforms. Here we adopt quasi-equilibrium states to approximate the leading order evolution of binaries, whereby we find that a lower bound on the scalar mass of $m_\phi\gtrsim10^{-11}$ eV is suggested by the event GW170817 if the progenitors were spontaneously scalarized.

Speaker: Hao-Jui Kuan (Max Planck Institute for gravitational physics)

17:00 Characterization of accretion discs from binary neutron star mergers

Accretion discs formed in binary neutron star (BNS) mergers are the engine responsible for many relevant physical processes. Numerical simulations of accretion discs have been used to investigate the outcome of such processes, but the initial configuration of the disc lack of an unique analytical description and some assumptions are still needed. In this work we analyze in detail the properties of accretion discs from 44 BNS merger simulations, with the aim of furnishing reliable initial conditions and a comprehensive characterization of the accretion discs. We found that the discs are thick, with an aspect ratio decreasing with the mass ratio of the binary from ∼ 0.7 to 0.3. Despite the disc sample spans a broad range in mass and angular momentum, their ratio is independent on the equation of state (EOS) and on the mass ratio of the binary. We have found that this can be traced back to the rotational profile of the disc, characterized by a constant specific angular momentum of 3 − 5 × 10¹⁶ cm² s⁻¹. The entropy per baryon and the electron fraction depend on the mass ratio of the binary. For small mass ratio they follow a sigmoidal distribution with the density, for which we provide a detailed description and a fit. The disc properties discussed in this work can be used as a robust set of initial conditions for future long-term simulations of accretion discs from BNS mergers, posing the basis for a progress in the quantitative study of the outflow properties.

Speaker: Alessandro Camilletti (Istituto Nazionale di Fisica Nucleare)

17:00 Diagrammatic Effective Field Theory approach to coalescing binary systems in General Relativity and gravitational waves phenomenology

An accurate modeling of the gravitational waves emitted by coalescing binary systems, comprising black holes and neutron stars, is fundamental to fully leverage the capabilities of current and next-generation gravitational wave detectors.
In particular the inspiral phase of the binary system can be described using several approximation schemes, among which the post-Newtonian (PN) formalism.
In the last 20 years the evaluation of higher order post-Newtonian corrections has advanced further thanks to an Effective Field Theory approach and the application of multi-loop quantum field theory techniques. We study this modern approach, implementing the whole evaluation of conservative diagrams in a Mathematica code, which allows to compute also some conservative diagrams first appearing at 7PN order.
Then, employing a Fisher Information Matrix analysis, we forecast the constraints that the future space-based LISA interferometer will be able to provide regarding parametric deviations from the post-Newtonian theory.

Speaker: Dr Matteo Pegorin (University of Padua)

17:00 Gravitational Wave Signals from Binary-Single Black Hole Encounters in Star Clusters

Star clusters are the dynamical formation channel for binary black holes (BBHs). In these dense systems, BBH mergers are not only driven by gravitational wave (GW) emission but also by binary-single encounters with other objects in the environment. The focus of the talk will be on the GW signals generated by close encounters between a BBH and a third black hole. We characterized diverse GW signatures, that are produced through numerical simulations using stellar mass black holes as input masses. The talk will also consider the potential for these burst signals to fall within the sensitivity band of current and future ground-based detectors, depending on the parameters involved.

Speaker: Ms Elena Codazzo (GSSI and INFN)

17:00 Impact of dark matter spikes on the merger rates of Primordial Black Holes

Primordial Black Holes (PBHs) may form in the early Universe by formation mechanisms such as large density fluctuations, bubble collisions, collapse of domain walls or collapse of cosmic strings. PBHs are considered as one of the possible candidates for dark matter. A huge amount of work has been done on PBHs because it is considered that the merger of PBHs binaries can also lead to the origin of gravitational waves seen by LIGO/VIRGO/KAGRA (LVK) Scientific Collaboration. We study the current merger rate of PBHs binaries based on the assumption that PBHs are non-particle candidates of dark matter having a spike of non-annihilating cold dark matter particles such as axions around them. For that we extend the previous calculations of the merger rate of PBH binaries for extended PBH mass functions. Using analytical and numerical approaches, we calculate the current merger rates of PBH binaries with DM spikes assuming that either the DM spikes are completely thrown out of the binaries or they remain static during the merger. We found that the presence of DM spikes alters the distribution of final merger time and size of binaries in such a way that it can lead to either increase or decrease in the merger rate of PBH binaries, in comparison to the PBH binaries without DM spikes. Also, the binary black hole mergers seen in third Gravitational-Wave Transient Catalog (GWTC - 3) of LVK Collaboration can be very well explained by the mergers of PBH binaries with and without DM spikes for Lognormal and Power Law mass function (MF) in PBH mass range 5 M⊙ ≤ mpbh ≤ 100 M⊙ and 10−2 M⊙ ≤ mpbh ≤ 100 M⊙ respectively, leading to fpbh ≤ O(10−5 − 10−3) which is consistent with the previous results. As per our assumptions about the presence of DM spikes around PBHs, this work applies very well to the binaries having either comparable PBH masses or highly assymetric PBH masses, but a general formalism can be developed in future which can apply to binaries having PBHs in any mass ratios.

Speaker: Dr Pratibha Janga (IFCA)

17:00 Measuring eccentricity in binary black hole mergers

Measuring eccentricity from gravitational wave signals is of fundamental importance in order to address questions about the origin and formation of stellar-mass binary black holes. In this work we present a new, systematic set of spinning but non-precessing numerical relativity (NR) simulations of eccentric binary black hole coalescences, with initial eccentricities up to 0.3 and mass ratios between 1 and 4. We develop a robust pipeline for measuring the eccentricity evolution from numerical relativity waveforms that is applicable even to short-duration signals. We investigate the reliability of this procedure by quantifying its accuracy and assess how the length of the NR waveform impacts the measurement of eccentricity, especially when extrapolating to low frequencies. Using the measured values of eccentricity as initial conditions, we generate effective-one-body waveforms and quantify how the precision in the eccentricity measurement, and therefore the choice of the initial conditions, impacts the agreement with the NR data. We find that even small deviations in the initial eccentricity can lead to non-negligible differences in the phase and amplitude of the waveforms. However, we find that we can reliably match the eccentricities between NR data and analytic models, which is crucial for robustly building eccentric hybrid waveforms, and can subsequently be used to improve the accuracy of models in the strong-field regime.

Speaker: Alice Bonino (University of Birmingham)

17:00 On the Testability of the Quark-Hadron Transition Using Gravitational Waves From Merging Binary Neutron Stars

Elementary particles such as quarks and gluons are expected to be fundamental degrees of freedom at ultra high temperatures or densities, while natural phenomena in our daily lives are described in terms of hadronic degrees of freedom. Massive neutron stars and remnants of binary neutron star mergers may contain quark matter, but it is not known how the transition from hadron matter to quark matter occurs. Different transition scenarios predict different gravitational waveforms emitted from binary neutron star mergers. If the difference between the equations of state only occurs at sufficiently high density, it is expected that the difference between waveforms mainly appears in the merger or the post-merger phase rather than in the inspiral phase. The typical frequency of gravitational waves after the coalescence is higher than 2 kHz, which is difficult to observe using current detectors. In this work, we performed Bayesian model selection for two scenarios proposed as representatives in Fujimoto et al. (2023) and investigated whether observations with future detectors will allow us to identify the correct model. We assume that the relatively low density equation of state around the nuclear saturation density is completely known from accumulated observations. Under this assumption, we find that it is reasonable to expect to be able to identify the correct transition scenario with third-generation detectors or specialized detectors with high sensitivity at high frequencies designed for post-merger signal observation, e.g., NEMO (Ackley et al. 2020).

Speaker: Reiko Harada

17:00 Targeted search for continuous gravitational waves from pulsars in binary systems in O3: a semi-coherent approach

The detection of continuous gravitational wave emission from a neutron star in a binary system is challenging for present and future LIGO-VIRGO-KAGRA searches. The motivation is the accurate modelling of the phase that depends on the binary orbital parameters. Indeed, even when the parameters are known within some uncertainties, search strategies are usually computationally prohibitive due to the necessity of exploring a large parameter space.
In this poster, I will present a new semi-coherent method that, given an ephemeris with uncertainties on binary orbital parameters, can detect the GW signal efficiently in a feasible computational time.

Speaker: Lorenzo Mirasola (INFN Cagliari/Cagliari University)

17:00 Tidal disruption of self-interacting axion clouds around black holes in binary systems

Black hole superradiance induces the formation of a cloud of ultralight bosons, such as axions. To detect the signature of the cloud, it is important to consider black holes in binary systems. As a binary inspirals and the separation becomes sufficiently small, the cloud is disrupted by the tidal interaction from the companion. Although axions generally have self-interactions, this effect has so far been ignored in this context. Taking into account the self-interaction, it is shown that the growth of the cloud saturates due to the dissipation and the lifetime becomes longer. Therefore, we investigate the evolution of the cloud in a binary system with self-interaction and present the formulation to solve it. We show the boundary of the orbital frequency where the cloud is disrupted and mention the possibility of bosenova collapse of the cloud.

Speaker: Takuya Takahashi (Kyoto University)

20:00 → 00:00 Social Dinner

Friday, 27 October

09:00 → 10:00 Black Holes Astrophysics

Conveners: Giuseppe Di Somma (University of Pisa), Lucia Papalini (University of Pisa)

09:00 Binary black holes at the dawn of the Universe

Speaker: Michela Mapelli (Padova University)

09:30 The effects of orbital precession on hyperbolic encounters

The hyperbolic encounters of two massive objects are characterized by the emission of a gravitational wave burst, with most of the energy released during the closest approach (near the periastron). The detection of such events, different from the well-known inspiral emission, would be an interesting discovery and provide complementary information to observations of binary mergers of black holes and neutron stars in the observable Universe, shedding light, for instance, on the clustering properties of black holes and providing valuable hints on their formation scenario. Here, we analyse the dynamics of such phenomena in the simplest case where two compact objects follow unbound/hyperbolic orbits. Moreover, we explore the effects of orbital precession on the gravitational wave emission, since the precession encodes certain general relativistic effects between two bodies. We also provide templates for the strain of gravitational waves and the power spectrum for the emission, and analytical expressions for the memory effect associated with such signals.
(Based on arXiv:2307.00915)

Speaker: Marienza Caldarola (Instituto de Física Teórica UAM-CSIC)

Caldarola - GraSP23.pdf

10:00 → 11:00 Machine Learning for Gravitational Waves

Conveners: Giuseppe Di Somma (University of Pisa), Lucia Papalini (University of Pisa)

10:00 Simulation-based inference for gravitational waves

Speaker: Stephen Green (University of Nottingham)

10:30 Generative Adversarial Networks applications for gravitational wave analyses

Speaker: Ik Siong Heng

11:00 → 11:30 Coffee Break

11:30 → 12:30 Gravity in the weak field

Conveners: Giuseppe Di Somma (University of Pisa), Lucia Papalini (University of Pisa)

11:30 GINGER

The Earth's rotation rate variations, certainly important for Earth science, are relevant also for fundamental physics investigation, as they contain general relativity terms, such as de Sitter and Lense Thirring, and unique data to investigate Lorentz violations. Long term continuous operation and very high sensitivity are required, the limit to be reached to study fundamental physics is 1 part in $10^{9}$ of the Earth rotation rate. Present large ring laser gyroscopes achieve record levels of performance in the measure of absolute angular rotation, and have already proved the required sensitivity.
The GINGER project is based on an array of ring lasers, its apparatus is described in detail with special attention to its sensitivity limits.

Speaker: Angela Dora Vittoria Di Virgilio (Istituto Nazionale di Fisica Nucleare)

DiVirgilioGRASP2023.pdf

12:00 Advancements in geodetic observations with large ring laser gyroscopes

A multitude of different globally distributed and independent mass transport phenomena lead to non-predictacle fluctuations in the Earth's rotation rate $\Omega_{e}$. Large Sagnac interferometers in the form of ring lasers enable the instantaneous observation of variations in $\Omega_{e}$ at a level of a few ppb. Here, the benefit of this technique, as well as recent advancements and future possibilities are discussed.

Speaker: Jannik Zenner (University of Bonn)

12:30 → 13:00 Neutron Stars: Matter at the Extremes

Conveners: Giuseppe Di Somma (University of Pisa), Lucia Papalini (University of Pisa)

12:30 Modeling the strong-field dynamics of binary neutron star merger

Binary neutron star mergers (BNSM) are cosmic collisions of compact
stars associated to powerful gravitational and electromagnetic
astronomical transients. Multimessenger observations of BNSMs promise
to deliver unprecedented insights on fundamental physics questions,
including constraints on dense matter models and the production of
heavy elements. Detailed theoretical predictions of the merger
dynamics are a crucial aspect for extracting information from such
observations. This talk reviews recent progress on the modeling of
BNSMs using simulations in 3+1 numerical general relativity. In the
first part, I will discuss predictions for the complete
(inspiral-merger-postmerger) gravitational-wave spectrum and their
application in gravitational-wave astronomy. In the second part, I
will discuss merger remnants and mass ejecta, the mechanisms behind
kilonova light and the application of these results to the analyses of
astrophysical data.

Speaker: Prof. Sebastiano Bernuzzi

15:00 → 17:30 Virgo Tour