Black holes and their symmetries

2 juil. 2025, 09:00 → 4 juil. 2025, 18:00 Europe/Paris

E2050 (Tours)

The aim of the workshop is to bring together the international experts in the classical and quantum  black holes, making particular focus on the symmetries. More precisely, the following themes will be in the focus:

• Black holes with hairs
• Quasi-normal modes and their symmetries
• Asymptotic symmetries: BMS and Carrollian
• Lower-dimensional models of black holes
• Horizonless compact objects as BH mimickers

 

Local organizers:  Xavier Bekaert, Yannick Herfray, Loic Villain,  Sergey Solodukhin, Michael Volkov, Laetitia Portier 

There is no formal registration. Those interested in participating are invited to send  a message to sergey.solodukhin@univ-tours.fr

 

Photo1.jpg

Photo2.jpg

Photo3.jpg

Photo4.jpg

mer. 2 juillet

09:30 → 10:15 Coffee/Registration

10:15 → 11:00 Third law of black hole mechanics for supersymmetric black holes

Orateur: Harvey Reall

tours.pdf

11:00 → 11:45 Symmetries and peeling in the extremal Reissner-Nordström spacetime

Orateur: Eric Gourgoulhon

sym_ern.pdf

12:00 → 14:00 Lunch

14:00 → 14:45 Semiclassical aspects of two-dimensional black holes: singularity resolution via a negative central charge

We analyze the semiclassical geometry of two-dimensional (CGHS) black holes in the Boulware vacuum. In this state, the expectation value of the stress-energy tensor is singular at the classical horizon. However, when backreaction effects are taken into account, the resulting geometry becomes horizonless and takes the form of a non-symmetric wormhole, featuring a curvature singularity beyond the throat. Remarkably, reversing the sign of the central charge of the conformal matter eliminates this singularity, yielding a backreacted geometry that is both horizonless and asymptotically flat. We argue that this behavior is largely universal, independent of the specific local counterterm added to the non-local Polyakov action. This result aligns with recent findings obtained in the semiclassical analysis of Schwarzschild geometry within the framework of two-dimensional dilaton gravity. We also discuss the physical significance of negative central charges in conformal anomalies from a four-dimensional perspective.

Orateur: Jose Navarro Salas

1 Talk Tours Navarro-Salas 2D Gravity and singularity resolution.pdf

14:45 → 15:30 Deforming black holes and ultracompact objects from the inside and from the outside

Orateur: Carlos Barcelo Seron

BHuniqueness.pdf

15:30 → 16:00 Coffee Break

16:00 → 16:45 Killing horizon data

Orateur: Marc Mars

Tours_Mars_shortened.pdf

16:45 → 17:30 Exotic properties of strongly interacting matter under acceleration and rotation

Recent first-principles lattice simulations of SU(N) Yang-Mills theory in 3+1 dimensions have revealed that the gluon plasma—a precursor to the quark-gluon plasma believed to have existed in the early Universe—exhibits several unexpected equilibrium properties under extreme conditions: (i) a negative moment of inertia within a certain temperature range; (ii) the formation of a thermodynamically stable inhomogeneous mixed phase that does not align with the conventional Tolman–Ehrenfest relation in static gravitational backgrounds; (iii) a rotation-induced enhancement of the critical deconfinement temperature; and (iv) a pronounced softening of the deconfinement transition under linear acceleration. We briefly review these surprising observations and argue that they may share a common origin rooted in the nontrivial coupling of gluonic degrees of freedom to strong gravitational fields, particularly in rotating or accelerated frames.

Orateur: Maxim Chernodub

Chernodub_talk_Tours.pdf

18:00 → 20:00 Wine and cheese

jeu. 3 juillet

09:00 → 09:45 Gravitational wave generation beyond General Relativity

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.

Orateur: Barausse Enrico

Tours25.pdf

09:45 → 10:15 Coffee Break

10:15 → 11:00 Gravitational wave tests of generic EFT-inspired theories of gravity

Orateur: Laura Bernard

Pres_Tours_Laura_Bernard.pdf

11:00 → 11:45 Black hole binaries in an expanding Universe

According to the Λ-Cold Dark Matter (ΛCDM) model, a positive cosmological constant explains
the accelerated expansion of the Universe. We start by constructing a static solution of general
relativity with a positive cosmological constant that consists of two (or more) static black holes
whose gravitational attraction is balanced by the cosmic expansion of the de Sitter background.
Then, we extend our analysis and establish the existence of stationary, spinning black binaries in a
de Sitter universe and analyse their properties (there is no quadrupole momenta, no radiation). We
consider identical black holes with either aligned or anti-aligned spins which maximize the spin-spin
repulsion or attraction, respectively. We discuss the prospect that spin-spin interactions can stabilize
the binaries. Our solutions establish continuous non-uniqueness in general relativity without matter
(we have several solutions with the same cosmological entropy and angular momentum) for the first
time in four dimensions. They evade assumptions of mathematical theorems that would otherwise
rule out their existence. They also provide initial data for the spinning binary merger problem (when
orbital angular momentum is added).

Orateur: Oscar Dias

dS-binary-Tours-July2025.pdf

12:00 → 14:00 Lunch

14:00 → 14:45 Hearts of Darkness: the inside-out probing of black holes

The standard paradigm of black holes, rooted in Einstein's General Relativity, predicts the existence of singularities. However, the emergence of quantum gravity candidates and new observational technologies have opened the door to exploring regular black holes and black hole mimickers as viable alternatives. These non-singular solutions, which replace the central singularity with a finite-core structure, challenge traditional concepts and offer a path towards understanding gravitational collapse beyond Einstein's framework. In this talk, I will discuss the theoretical foundations of regular black holes and black hole mimickers, and their possible instabilities and phenomenology. I will further explore their observational signatures, ranging from gravitational wave echoes to modifications in black hole images, as a means to distinguish them from classical black holes. In the end I will argue that by leveraging recent advancements in observational astrophysics, we might be at the dawn of a new era for quantum gravity phenomenology.

Orateur: Stefano Liberati

Tours-2025-Liberati.pdf

14:45 → 15:30 Simplicity and Universality in (Binary) Black Hole dynamics: an integrability f-Airy tale

Orateur: Jose Luis Jaramillo

fAiry_BBHmerger_2025_Tours_v2.pdf

15:30 → 16:00 Coffee Break

16:00 → 16:30 Investigation of Non-Symmetric Black Hole Mimickers

This presentation explores the classification of various configurations of
non-symmetric black hole mimickers, limited by the conditions
of spacetime regularity and geodesic completeness. For physically viable models, test metrics will be presented, and their parameters will
be analyzed in light of observational data from black hole shadow
experiments. Furthermore, scalar perturbations and the associated
quasinormal modes arising in these spacetimes will be discussed.

Orateur: Vagif Tagiev

16:30 → 17:00 Black holes with electroweak hair I

Orateur: Mikhael Volkov

Volkov-Tours.pdf

17:00 → 17:30 Black holes with electroweak hair II

Orateur: Romain Gervalle

Présentation_Black_Hole_Symmetries.pdf

ven. 4 juillet

09:00 → 09:45 Null infinity as a weakly isolated horizon

I will present a common description of null infinity and physical
horizons, highlighting the geometric properties they share, and the
origin of the radically different physics they describe. The common
description offers new perspectives on the different symmetry groups
considered at finite distance. I will then show how ambiguities in the
construction of charges from Noether's theorem are removed using a
prescription due to Wald and Zoupas, for both null infinity and the
finite distance case, and how the results match with the method by
Ashtekar and Streubel. I will then show how the method of Barnich and
Brandt can be also brought in agreement, in particular how the
covariance requirement removes any field-dependent 2-cocycle in the
realization of the symmetry algebra. Finally, I will summarize the
status of the Wald-Zoupas prescription for different enlargements of
the BMS symmetry currently under study.

Orateur: Simone Speziale

09:45 → 10:15 Coffee Break

10:15 → 11:00 Equivalence Principle and generalised accelerating black holes from binary systems

Orateur: Marco Astorino

11:00 → 11:45 Gravitational S-matrix, infrared divergences and BMS representations

Orateur: Yannick Herfray

12:00 → 14:00 Lunch

14:00 → 14:45 Dynamical formation of regular black holes

Orateur: Pablo Bueno

14:45 → 15:30 Some unconventional enhanced black hole symmetries with physical implications

Exact continuous symmetries play a central role in constraining black hole dynamics. In this talk, I will discuss two examples of non-exact or non-continuous enhanced black hole symmetries that also have physical implications. One is the manifestation of SL(2,R) symmetries within the near-zone region, a region that extends beyond the near-horizon regime and has a non-empty overlap with the far region. This near-zone (``Love’’) symmetry, albeit approximate in its nature, has the ability to address instances of magic zeroes in the black hole response problem: it outputs the vanishing of the static Love numbers as a selection rule. The other symmetry I will talk about emerges for some asymptotically flat extremal black holes and comes in the form of spatial inversions. First identified by Couch & Torrence, these spatial inversions conformally map the degenerate event horizon onto null infinity, and vice versa. This mapping enforces matching conditions between near-horizon and near–null-infinity data, a direct consequence being the identification between infinite towers of conserved quantities: the near-horizon Aretakis constants and the near–null-infinity Newman-Penrose constants.

Orateur: Panagiotis Charalambous

15:30 → 16:00 Coffee Break

16:00 → 16:45 The memory effect : from numerical to analytic study

The displacement of particles hit by a burst of gravitation waves called the Memory Effect, proposed by Braginski, Thorne, Zel'dovich, Polnarev, and others, is studied. The original proposal of Gibbons and Hawking admits only numerical solutions, however ingeneous approximations of the wave profile allow to find analytic solutions.

Orateur: Peter Horvathy

Horvathy_Tours_July.pdf