### Mini Workshop

#### New horizons for horizonless physics: from gauge to gravity and back again

###### This event can be attended either in presence or on line

**Apr 17, 2023 - Apr 21, 2023**

**Abstract**

Motivated by the recent breakthroughs in GW astronomy and in radio imaging of BHs, the last few years have witnessed a growing interest in exploring the phenomenology of BHs, compact objects and horizonless micro-states which emerge in the 'fuzzball' proposal in string theory. Semi-analytical, fully numerical techniques and, more recently, exact methods from gauge theory and 2d CFT have been developed by different communities to study the linear response to perturbations of BHs and compact objects, their multipolar structure, tidal deformation properties and absorption coefficients that are crucial to model the GW signal expected from the merger of these objects and discriminate signatures of new physics at the horizon scale. The goal of this workshop series is to bring together scientists from different communities, backgrounds and expertise, to stimulate interdisciplinary interactions between ideas and techniques as diverse as gauge theories, 2d CFT, BH and GW phenomenology, string theory, and advanced numerical techniques.

**Topics**

Speakers: Enrico Barausse (SISSA, Italy), Iosif Bena (Saclay, France), Ram Brustein (Ben Gurion University), Vitor Cardoso (IST, Portugal and Niels Bohr, Denmark), Nejc Ceplak (IPHT, France), Anna Ceresole (INFN, Torino), Sumanta Chakraborty (Kolkata, India), Giorgio Di Russo (Tor Vergata, Italy) , Pierre Heidmann (Johns Hopkins, USA), Tanja Hinderer (Utrecht, The Netherlands), Cristoforo Iossa (SISSA, Italy), Stefano Massai (Padua University), Daniel Mayerson (Leuven, Belgium), Costantino Pacilio (Bicocca, Italy), Riccardo Penco (Carnegie Mellon University, USA), Davide Perrone (Geneva, Switzerland), Rodolfo Russo (Queen Mary, UK) and Nicholas P. Warner (IPHT, France and Southern California, USA).

**Organizers**

Massimo Bianchi (Universita’ di Roma “Tor Vergata”);

Giulio Bonelli (SISSA);

MariaLuisa Frau (Universita’ di Torino);

Francesco Fucito (INFN Roma "Tor Vergata")

Jose Francisco Morales (INFN Roma "Tor Vergata");

Paolo Pani (Universita’ di Roma “Sapienza”);

Alessandro Tanzini (SISSA);

**Local organizer**

Jose Francisco Morales

**Contact**

morales@roma2.infn.it

**Talks**

Date | Speaker | Title | Type | Useful Links | ||||
---|---|---|---|---|---|---|---|---|

Apr 17, 2023 - 11:15-12:00 | Ram Brustein (Ben Gurion University) |
TBA | Seminar | Video | ||||

Apr 17, 2023 - 12:00-12:45 | Nejc Ceplak (IPHT Saclay, Paris, France) |
The Correspondence Between Rotating Black Holes and Fundamental Strings | Seminar | Slides | Video | |||

Apr 17, 2023 - 14:00-14:30 | Giorgio Di Russo (University of Rome "Tor Vergata") |
TBA | Seminar | |||||

Apr 17, 2023 - 15:00-16:00 | Chairman: Massimo Bianchi (University of Rome Tor Vergata) |
Discussion & Lightning Talks | Discussion | |||||

Apr 18, 2023 - 10:00-10:45 | Vitor Cardoso (Niels Bohr Institute and Lisbon, IST) |
New horizons: t esting the black hole paradigm | Seminar | Slides | Video | |||

Apr 18, 2023 - 11:15-12:00 | Riccardo Penco (Carnegie Mellon University, USA) |
The naturalness of vanishing black hole response | Seminar |
Abstract
Black holes in 4D General Relativity have the remarkable property that they lack any form of static linear response. At length scales much larger than the Schwarzschild radius, where black holes can be described as point particles, their linear response is captured by an infinite number of Wilson coefficients in the worldline action. From this perspective, the absence of static linear response would appear to pose a naturalness problem for the point-particle effective theory. In this talk, I will discuss a recently discovered network of hidden symmetries of the action for black hole perturbations. Some of these symmetries act non-trivially on the long-distance variables in the point-particle effective theory, and force the linear response coefficients to vanish, thus solving the naturalness problem. |
Slides | Video | ||

Apr 18, 2023 - 14:00-14:45 | Davide Perrone (University of Geneva) |
TBA | Seminar | Video | ||||

Apr 18, 2023 - 14:45-15:15 | Costantino Pacilio (University of Milan Bicocca, Italy) |
Black hole spectroscopy with the next generation of gravitational wave detectors | Seminar |
Abstract
Black hole spectroscopy is the measurement of the quasi normal mode spectrum in the gravitational waves emitted by a perturbed black hole. Detecting multiple excited modes provides an excellent opportunity to test the dynamics of general relativity in the strong field regime. Third generation detectors will lead to a large increase in the ringdown signal-to-noise ratio (SNR), which will allow us to identify routinely subdominant excited modes besides the dominant one. We use a simulated catalog of merging stellar mass binary black holes to investigate the prospects of black hole spectroscopy with ground based third generation detectors. We study the cumulative distribution in the ringdown SNR and quantify the precision with which the quasi normal modes will be measured during the operational time of the detectors. Overall, we find that third generation detectors will be able to detect several thousands of ringdown events per year, with O(10) golden events per year with SNR larger than 100. Next, we find that about a thousand events per year will constrain deviations from general relativity in the spectrum with better than 10 per cent precision in the individual events. Finally, we discuss the prospects for constraining deviations from general relativity when stacking together the population of the detected events. |
Slides | |||

Apr 18, 2023 - 15:15-15:45 | Chairman: Paolo Pani (University of Rome Sapienza, Italy) |
Discussion | Discussion | |||||

Apr 19, 2023 - 10:00-10:45 | Nicholas P. Warner (IPHT, France and Southern California, USA) |
TBA | Seminar | Video | ||||

Apr 19, 2023 - 11:15-12:00 | Pierre Heidmann (Johns Hopkins University, USA) |
Geometric Resolution of Schwarzschild Horizon | Seminar |
Abstract
I will present a new technique to construct non-extremal solitons in gravity with compact dimensions. They correspond to smooth horizonless geometries induced by topology in spacetime and supported by electromagnetic flux, which characterize coherent states in quantum gravity. I will present various types of solutions contained in the ansatz such as topological stars and bubble bag ends. Then I will focus on neutral topological solitons that are indistinguishable from Schwarzschild black holes with a scalar field, called Schwarzschild scalarwall, but replace the horizon at r=2M with a smooth bubbling geometry. This is the first example of such a geometric transition in string theory for astrophysically relevant black holes. I will conclude by discussing some of their gravitational signatures |
Slides | Video | ||

Apr 19, 2023 - 14:00-14:30 | Iosif Bena (Saclay, France) |
The amazing Super-Maze | Seminar | Slides | Video | |||

Apr 19, 2023 - 14:30-15:00 | Daniel Mayerson (Leuven, Belgium) |
EfFOORTlessly simulating observable signatures of microstructure in black hole imaging | Seminar | Slides | Video | |||

Apr 19, 2023 - 15:00-15:30 | Chairman Francesco Fucito (INFN, Rome Tor Vergata, Italy) |
Discussion | Discussion | |||||

Apr 20, 2023 - 10:00-10:45 | Tanja Hinderer (Utrecht University, The Netherlands) |
TBA | Seminar | Video | ||||

Apr 20, 2023 - 11:15-12:00 | Enrico Barausse (SISSA, Italy) |
TBA | Seminar | Video | ||||

Apr 20, 2023 - 14:00-14:30 | Cristoforo Iossa (SISSA, Italy) |
TBA | Seminar | Video | ||||

Apr 20, 2023 - 14:30-15:00 | Sumanta Chakraborty (Kolkata, India) |
Probing Quantum Effects at the Horizon Through Gravitational Waves | Seminar | Slides | Video | |||

Apr 20, 2023 - 15:00-15:30 | Chairman Anna Ceresole (INFN, Section of Turin, Italy) |
Bridging between the classical and quantum 2-body problem | Discussion | |||||

Apr 21, 2023 - 10:00-10:45 | Rodolfo Russo (Queen Mary, London, UK) |
Gravitational scattering at high energies | Seminar | Slides | Video | |||

Apr 21, 2023 - 11:15-12:00 | Stefano Massai (Padua University) |
TBA | Seminar | Video | ||||

Apr 21, 2023 - 12:00-12:30 | Chairman Giulio Bonelli (SISSA, Trieste, Italy) |
Discussion | Discussion |