Third law of black hole mechanics for supersymmetric black holes

• Harvey Reall

Room: E2050

Symmetries and peeling in the extremal Reissner-Nordström spacetime

• Eric Gourgoulhon

Room: E2050

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

• Jose Navarro Salas

Room: E2050 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.

Deforming black holes and ultracompact objects from the inside and from the outside

• Carlos Barcelo Seron

Room: E2050

Killing horizon data

• Marc Mars

Room: E2050

Exotic properties of strongly interacting matter under acceleration and rotation

• Maxim Chernodub

Room: E2050 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.

Gravitational wave generation beyond General Relativity

• Barausse Enrico

Room: E2050 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.

Gravitational wave tests of generic EFT-inspired theories of gravity

• Laura Bernard

Room: E2050

Black hole binaries in an expanding Universe

• Oscar Dias

Room: E2050 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).

Hearts of Darkness: the inside-out probing of black holes

• Stefano Liberati

Room: E2050 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.

Simplicity and Universality in (Binary) Black Hole dynamics: an integrability f-Airy tale

• Jose Luis Jaramillo

Room: E2050

Investigation of Non-Symmetric Black Hole Mimickers

• Vagif Tagiev

Room: E2050 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.

Black holes with electroweak hair I

• Mikhael Volkov

Room: E2050

Black holes with electroweak hair II

• Romain Gervalle

Room: E2050

Null infinity as a weakly isolated horizon

• Simone Speziale

Room: E2050 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.

Equivalence Principle and generalised accelerating black holes from binary systems

• Marco Astorino

Room: E2050

Gravitational S-matrix, infrared divergences and BMS representations

• Yannick Herfray

Room: E2050

Dynamical formation of regular black holes

• Pablo Bueno

Room: E2050

Some unconventional enhanced black hole symmetries with physical implications

• Panagiotis Charalambous

Room: E2050 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.

The memory effect : from numerical to analytic study

• Peter Horvathy

Room: E2050 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.