Alexandre Belin : Discussion on ensemble averages in holography
Francesco Benini : Entanglement and symmetry breaking
Abstract: Entanglement asymmetry is a recently introduced quantum-information-based observable that detects symmetry breaking in quantum states on subsystems and out of equilibrium. After reviewing this observable, I will describe how to compute it in CFTs for a class of coherent states in a perturbative expansion. I will present explicit formulas for various subsystem geometries as well as for its time dependence, exhibiting in some cases the quantum Mpemba effect. The class of states we consider have a simple holographic description, allowing us to present a dual holographic computation of entanglement asymmetry. This might have interesting applications to the study of quantum properties of charged black holes.
Jan Boruch : Indices from the gravitational path integral - new forms of attraction
Abstract: In recent years, the Euclidean gravitational path integral has proven to be a reliable tool for studying quantum mechanical aspects of black holes. An important quantity that can help us probe whether black holes behave like conventional quantum mechanical systems is the supersymmetric index computed directly from the gravitational path integral. In this talk, I will discuss the issue of multicentered black hole contributions to the Euclidean path integral that computes the supersymmetric index at finite temperature. In the context of Einstein-Maxwell theory in 4d, I will explain how the multicentered generalization of the Kerr Newman black hole, called the Israel-Wilson solution, can be seen to satisfy the boundary conditions of the supersymmetric index and yields a regular contribution to the index. I will show how even though we perform the computations at finite temperature, the construction makes the value of the on-shell action depend only on the black hole charges, which can be viewed as a new form of the attractor mechanism. Finally, I will describe how we can extend the analysis to the most general solutions of N=2 4d supergravity, where the on-shell action becomes independent of the boundary values of the scalars. Time permitting, I will describe how the phenomenon of wall-crossing, in which the index jumps discontinuously as one crosses a codimension one wall in the space of asymptotic scalar moduli, arises from the perspective of the new finite temperature saddles.
Based on 2310.07763 and an upcoming work with Luca Iliesiu, Sameer Murthy and Joaquin Turiaci.
Alejandra Castro : Near-extremal black holes
Branislav Cvetković : Near horizon symmetry of extremal spacelike-stretched black holes
Abstract: We analyze the near horizon structure of the extremal spacelike stretched black holes, exact solutions of topologically massive gravity. We show that the algebra of improved canonical generator is realized as a single centrally extended Virasoro algebra. We obtain the entropy of the solution by using the Cardy formula and compare the results with the corresponding non-extremal case.
Nejc Čeplak : What is on the horizon for fuzzballs
Abstract: The Fuzzball proposal is a proposal for the resolution of the information paradox and the entropy problem of black holes. It states that conventional black holes should be replaced by horizonless microstates whose number reproduces the black hole entropy and that can be, in principle, realised in string theory.
In this discussion session, I will review some of the general arguments in favour of and against the fuzzball proposal. I will then briefly talk about the construction of some explicit black hole microstates within supergravity, often called microstate geometries, and discuss some of their most important properties and how these differ from conventional black holes. I will conclude with some future directions and connections with other works.
Marine de Clerck : Mixmaster chaos in AdS black hole interior
Abstract: Amongst the most fascinating behaviours to arise from Einstein's equations is the onset of chaotic dynamics in the approach to certain cosmological singularities. This was analysed in detail in seminal work by Belinskii, Khalatnikov, Lifshitz (BKL) and others some fifty years ago. A consequence of these results is that the Schwarzschild interior solution near the singularity appears very fine-tuned and should give way for BKL-like dynamics in more generic black holes. In our recent work (arxiv:2312.11622), we construct a setup that realises the so-called 'mixmaster' chaotic dynamics in the interior of an AdS black hole. After a brief review of the BKL work, I will describe our holographic setup and discuss the peculiar symmetries appearing in this problem.
Jan de Boer : Discussion on black hole interiors
Ben Freivogel : Quantum fluctuations in black holes
Alessandra Gnecchi : Black holes, swampland constraints, and higher form symmetry breaking
Abstract: The presence of black holes in the low energy spectrum of the gravitational EFT signals fundamental properties of the UV-complete, quantum gravity theory. We show how black holes constructed from string theory can be exploited to investigate swampland constraints, through their thermodynamics. Finally, we discuss BPS states in relation to the breaking of supergravity one-form symmetries, associated to abelian vector fields.
Dragoljub Gočanin : Holographic exploration of exotic bulk geometries
Abstract: In the context of AdS/(B)CFT duality, we discuss the possibility of having Riemann-Cartan bulk geometry that involves torsion. This is a crucial step towards a better understanding of spin systems, such as Fermi liquids, in holographic terms, and is also a base for holographic analysis of noncommutative gravity - a theory that goes beyond the classical notions of spacetime geometry. Due to its rich structure, the main focus is on 5D Chern-Simons gravity and related models.
Andrei Parnachev : Operator product expansion, geodesics and black hole singularities
Abstract: We observe features of black hole singularities in finite temperature holographic correlators. We also elucidate the relation between geodesics in AdS-Schwarzschild and the Operator Product Expansion in the boundary theory.
Philip Saad : Review of JT gravity
Chiara Toldo : Thermodynamics of near-extreme rotating black holes
Abstract: From the perspective of classical gravity, a black hole is the simplest object we know of. At the same time, it possesses huge entropy, hinting at an incredibly complex microstructure: understanding this fact falls in the realm of quantum gravity. In this talk I will review recent results concerning the microscopics and the thermodynamics of fast spinning black holes in asymptotically flat and Anti-de Sitter space. In the first part, I will describe how recently developed techniques allow to compute the quantum corrections to the entropy of near-extremal Kerr black holes. I will show that the quantum-corrected near-extremal entropy exhibits 3/2logT behavior characteristic of the Schwarzian model, and predicts a lifting of the ground state degeneracy for the extremal Kerr black hole. In the second part, I will show the computation for the density of states for fast spinning black holes in AdS4, which admit a supersymmetric limit, and comment on the spectrum of near-BPS states and on the interpretation in terms of the dual 3d field theory.