Asymmetric Binaries meet Fundamental Astro-Physics

20 Sept 2023, 14:00 → 22 Sept 2023, 19:00 Europe/Rome

GSSI

Gravitational wave observations of binary mergers are carrying a new revolution in astrophysics. While signals detected by ground based detectors have already shed light on the most violent among astrophysical events, next generation of interferometers like LISA will allow to witness the evolution of new families of sources, as asymmetric binaries, which harbour a unique potential for the identification of new fundamental fields and particles.

The workshop “Asymmetric Binaries Meet Fundamental Astro-Physics” builds around 5 topics connected to these compact sources: self-force methods, beyond GR modelling, Exotic Compact Objects, environmental effects, astrophysics and data analysis approaches.

The goal of the meeting is to discuss the most recent advances in these topics and their relevance to probe astrophysical and fundamental physics scenarios. We aim to foster multi-disciplinarity among the various themes.

The workshop will be held at the Gran Sasso Science Institute in L’Aquila, from September 20-22, 2023.

L’Aquila lives in a beautiful environment surrounded by the highest peaks of the Apennine Mountains of Italy. The city is home to art, history, and great food.

Invited Speakers

Enrico Barausse (SISSA)
Susanna Barsanti (Sapienza University)
Beatrice Bonga (Radboud University)
Richard Brito (Instituto Superior Tecnico)
Vitor Cardoso (Niels Bohr Institute)
Alvin Chua (University of Singapore)
Lisa Drummond (Massachusetts Institute of Technology)
Leanne Durkan (The University of Texas at Austin)
N. V. Krishnendu (International Center for Theoretical Studies)

Carlos Lousto (Rochester Institute of Technology)
Elisa Maggio (Albert Einstein Institute)
Maarten van de Meent (Niels Bohr Institute)
Paolo Pani (Sapienza University)
Gabriel Piovano (University College Dublin)

Laura Sberna (Albert Einstein Institute)
Pau Amaro Seoane (Universitat Politècnica de València)
Thomas Sotiriou (Nottingham University)
Lorenzo Speri (Albert Einstein Institute)
Andrew Spiers (Nottingham University)
Takahiro Tanaka (Kyoto University) 
Niels Warburton (University College Dublin)
Nico Yunes (University of Illinois)


Organizing Committee
Sara Gliorio, Leonardo Gualtieri, Andrea Maselli, Lavinia Paiella, Adam Pound
 

Scientific Committee
Leor Barack, Thomas Sotiriou, Barry Wardell, Nico Yunes

 

 

 

Group picture!

poster

Wednesday, 20 September

14:40 → 14:50 Registration

14:50 → 15:00 Welcome and practical information

15:00 → 18:00 Self Force

15:00 State of the art in gravitational self-force and the post-adiabatic inspiral in Schwarzschild

I will discuss what is the current state of the art for gravitational self-force waveforms and the ingredients that go into them. I will discuss how the second-order metric perturbation is used to calculate the amplitude, flux and phase of a gravitational wave and how the slowly-evolving first-order metric perturbation contributes to sourcing perturbations at second order. I will demonstrate the validity of the model as compared to numerical relativity simulations and effective-one-body theory, noting the interesting result that the small-mass ratio approximation remains valid for near-comparable mass ratio binaries in the non-spinning case for quasicircular orbits.

Speaker: Leanne Durkan (The University of Texas at Austin)

Durkan.pdf

15:30 Adiabatic radiation reaction to the constants of motion in Kerr

I review how to compute the adiabatic radiation reaction to the
constants of motion including the Carter constant in Kerr spacetime.
I also talk about extending these ideas to post-adiabatic order, i.e.,
one order higher in the mass ratio, which would significantly simplifies
the construction of the gravitational wave waveform necessary for
the observation of extreme mass-ratio in-spirals.

Speaker: Takahiro Tanaka (University of Kyoto)

Tanaka.pdf

16:00 Secondary spin in asymmetric binaries

Accurate models of large mass-ratio black hole binary systems must include post-geodesic corrections which account for forces driving the small body away from the geodesic. One such effect is called the spin-curvature force which occurs when the secondary spin associated with the smaller black hole couples to the curvature of the background spacetime. In recent years, considerable progress has been made in quantifying the effect of secondary spin on gravitational waves in asymmetric binaries. In this talk, I will review the principles governing spinning bodies in curved space time, outline progress that has been made in the domain of secondary spin corrections in recent years and discuss remaining open questions in the field.

Speaker: Lisa Drummond (MIT)

Drummond.pdf

16:30 coffee break

17:00 Discussion

Speakers: Carlos Lousto (Rochester Institute of Technology), Niels Warburton (University College Dublin)

Thursday, 21 September

09:00 → 11:50 Environmental Effects

09:00 Environmental effects and matter systematics for low-frequency gravitational wave astronomy

Despite the groundbreaking discoveries of the LIGO-Virgo-KAGRA collaboration, the full frequency spectrum of the gravitational wave sky is still largely unknown. The Einstein Telescope will push observations on Earth down to the seismic noise, while LISA will
open a window on the mHz gravitational wave band from space. At the same time, pulsar timing arrays, which have just detected a stochastic background signal, will keep exploring the gravitational wave universe at nHz frequencies. This forthcoming wealth of data requires not only waveform templates of exquisite precision, but also to revisit the commonly held assumption that gravitational wave signals are insensitive to the surrounding ambient medium. I will present examples in which the matter environment may affect, directly and indirectly, the gravitational wave signals from various sources for
pulsar timing arrays, LISA and possibly ET. I will argue that a complete understanding and modeling of these effects is crucial for making gravitational astronomy a precision science in the next decade.

Speaker: Enrico Barausse (SISSA)

Barausse.pdf

09:30 Detecting disk-induced environmental effects

Gravitational-wave observations of extreme mass ratio inspirals (EMRIs) hold incredible potential to probe gravity, astrophysical and exotic environments. One of the main effects of astrophysical environments is the torque exerted by gas disks of active galactic nuclei, which force the EMRI to “migrate” (mostly) inward like a planet. We present a Bayesian model-independent framework to detect and characterise these effects with LISA. We will also explore a new, potentially detectable interaction between magnetised stars and the disk.

Speaker: Laura Sberna (AEI)

Sberna.pdf

10:00 Dynamical tidal resonances in EMRIs

Resonances are ubiquitous in nature. In this talk, I will focus on resonances due to the interaction of two stellar-mass black holes orbiting a central massive black hole. Such tidal resonances will generically occur for Extreme Mass Ratio Inspirals (EMRIs), if nearby compact objects exist. By probing their influence on the EMRI waveform, we can in principle extract information about the environmental tidal field of the EMRI system, albeit at the cost of a more complicated EMRI waveform model.

Speaker: Beatrice Bonga (Radboud University)

Bonga.pdf

10:30 coffee break

10:50 Discussion

Speakers: Thomas Spieksma (Niels Bohr Institute), Vitor Cardoso (Niels Bohr Institute)

11:50 → 13:30 lunch break

13:30 → 23:00 Beyond GR & ECO

13:30 Detecting scalar charge with EMRIs

I will first discuss under which circumstances can black holes carry a scalar charge and what this implies for how that charge scales with the mass of the black hole. I will then use this insight to argue that EMRIs are an ideal system for searches of new fundamental scalars. I will lay out the framework for modelling EMRIs in this context and and present some first forecasts on LISA's ability to measure scalar charge. This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please contact the sender and delete the email and attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. Email communications with the University of Nottingham may be monitored where permitted by law.

Speaker: Thomas Sotiriou (University of Nottingham)

Sotiriou.pdf

14:00 Using EMRIs to detect scalar fields with LISA

The description of Extreme Mass Ratio Inspirals (EMRIs) in modified theories of gravity can be very complex. However, 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 two parameters: the scalar charge carried by the secondary and the scalar field mass. Using these simplifications, I will show how the two parameters affects the EMRI dynamics, how such changes get imprinted on the emitted signals, and the extremely promising results on the LISA ability to detect new fundamental fields.

Speaker: Susanna Barsanti (Sapienza University)

Barsanti.pdf

14:30 Self-Force in Scalar-Tensor Theories of Gravity: Perturbative Approach Beyond Linear Order

For precise measurements of EMRIs with LISA data, first-post-adiabatic accuracy EMRI models will be required. Great effort is being expelled in pursuing first-post-adiabatic models in General Relativity. However, to test our fundamental theory of gravity, we also need models in alternative theories. Scalar fields are ubiquitous in alternative theories of gravity. In this talk, we provide a framework for modelling EMRIs to first-post adiabatic accuracy in general scalar-tensor theories of gravity. In our perturbative approach, the background spacetime can be treated as Kerr, as discussed in the preceding talks and Ref. [PRL. 125, 141101]. Additionally, we produce an ansatz for the action of a point scalar charge experiencing a self-force. From these assumptions, we derive field equations for the metric and scalar field perturbations to second order. Moreover, we derive the equations of motion of the compact object to second order. Crucially, our formalism builds on inputs from the General Relativity calculation, and the additional contributions are no more challenging to calculate than the General Relativity self-force contribution.

Speaker: Andrew Spiers (University of Nottingham)

Spiers.pdf

15:00 coffee break

15:20 Extreme mass-ratio inspirals into black holes surrounded by scalar clouds

Scalar clouds can form through superradiant instabilities of massive scalar fields around spinning black holes and can also serve as a proxy for dark matter structures around black holes. They can potentially be detected through a number of signatures, including the possibility that they can affect the dynamics of binary black hole systems. In this talk, I will discuss recent work aiming at studying extreme-mass-ratio systems in which a small compact object inspirals around a supermassive black hole surrounded by a scalar cloud. In particular, I will present the first steps towards studying those systems in a fully relativistic setup (i.e. making use of tools from black hole perturbation theory).

Speaker: Richard Brito (Instituto Superior Tecnico)

Brito.pdf

15:50 Testing the horizon 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: Elisa Maggio (AEI)

Maggio.pdf

16:20 Gravitational wave based Tests of binary black hole nature: current and future prospects

Gravitational wave observations through the first three observational runs of ground-based detectors can reveal such sources' various astrophysical and fundamental physics aspects. Even though the current detections do not show evidence for alternate compact objects, the data can still not rule out their existence entirely. This talk aims to provide a status update on black hole mimicker tests and their observational signatures, starting from existing bounds from current detectors to future space-based detectors. Moreover, we discuss some recent developments focusing on spin-induced multipole-based tests.

Speaker: N.V. Krishnendu (International Centre for Theoretical Sciences)

Krishnendu.pdf

16:50 coffee break

17:10 discussion

Speakers: Nico Yunes (University of Illinois at Urbana-Champaign), Paolo Pani (Sapienza University)

20:00 conference dinner

Friday, 22 September

09:30 → 12:30 Astro & Data

09:30 Oligochromatic extreme-mass ratio inspirals.

In this talk I will explain that, although polychromatic EMRIs (the EMRIs we have been talking about until now) have a very low event rate at our Galactic Centre, but that early EMRIs, i.e. EMRIs which are far away from plunging, do contribute and since they are so close to us, the SNR can reach extreme values.

Speaker: Pau Amaro Seoane (Universitat Politècnica de València)

Amaro.pdf

10:00 Search, recovery or destroy a waveform template: how important are eccentricity evolution and post-adiabatic terms for asymmetric binaries?

Extreme mass-ratio inspirals (EMRIs) arguably stand out among the sources observable by LISA. Indeed, an EMRI waveform is a treasure cove of information on the binary because the gravitational wave is extremely sensitive to even the smallest perturbation. Detecting such a signal would allow us to test General Relativity with unprecedented precision, unique to EMRIs. Such incredible scientific potential comes with a price: modeling accurate waveforms is a challenging task in terms of analytic computations, numerical simulations, and data analysis. One may then wonder: when can we use approximate models? What is the impact of waveform systematic errors on parameter estimation? In this talk, I will (partially) address these questions by presenting the results of a Bayesian statistical analysis on systematic biases. In particular, the work assesses the importance of first-order post-adiabatic (1PA) terms for extreme and intermediate-mass ratio binaries. We employ state-of-the-art 1PA waveforms for circular equatorial orbits in Schwarzschild spacetime, which include the flux corrections due to second-order self-force and secondary spin. Finally, we also investigate the impact of mismodeling the evolution of eccentric orbits for adiabatic waveforms."

Speaker: Gabriel Piovano (University College Dublin)

GSSI_seminar.pdf

10:30 Testing General Relativity with LISA observations

The future gravitational wave observations of the Laser Interferometer Space Antenna (LISA) mission have a huge scientific potential to test General Relativity. The key to unlocking such potential is to develop accurate and fast beyond vacuum waveforms and an efficient data analysis pipeline. This talk will illustrate how to do this with Extreme Mass Ratio Inspiral (EMRI) systems. We will present a full Bayesian analysis to test General Relativity with EMRI systems endowed with a scalar field. We will show that observing a "golden" EMRI can constrain the scalar charge tighter than ground-based gravitational wave detectors. Finally, we will outline the key challenges we will face when testing General Relativity with LISA data.

Speaker: Lorenzo Speri (AEI)

Speri.pdf

11:00 coffee break

11:30 Discussion

Speaker: Alvin Chua (University of Singapore)