Talks

Beyond the Throat: The Full Story of Schwarzian Modes and Black Hole Entropy 

Lucas Acito

Recent theoretical advances have solidified our understanding of black holes as genuine quantum systems. As a black hole cools down toward zero temperature (the extremal limit), an enhanced symmetry emerges in its near-horizon throat, and the quantum fluctuations associated with this throat are governed by the so-called Schwarzian modes. These modes dominate the low-temperature physics and generate universal logarithmic corrections to the black hole entropy. While they are traditionally studied using effective two-dimensional descriptions confined to the throat, their behavior within the full four-dimensional spacetime geometry has remained elusive. In this talk, I will present newly developed techniques to compute and understand Schwarzian modes directly within the full geometry picture. Focusing on a Schwarzschild-AdS black hole with a hyperbolic (H2) Riemann surface, I will show how these modes can be derived from a purely geometric perspective, thereby extending the standard near-horizon analysis.

Classical and Quantum logarithmic soft graviton theorems

Gianni Boschetti

The logarithmic soft graviton theorem captures universal low-frequency features of gravitational radiation in four dimensions and reflects the long-range nature of gravitational interactions. In this talk I will review both the classical and quantum logarithmic soft theorems, emphasizing their derivation through asymptotic Einstein equations. I will then present a new perspective suggesting that the quantum logarithmic soft theorem may itself admit an asymptotic derivation, pointing toward a unified understanding of classical and quantum logarithmic effects in gravity.

Boundary bound states and integrable Wilson Loops in ABJM 

Maximiliano Gabriel Ferro 

Based on arXiv:2602.09195, we investigate integrable open spin chains in the context of holography, focusing on the scattering of excitations off a boundary carrying an internal degree of freedom. By imposing the preservation of the SU(1|2) boundary symmetry, we construct the most general reflection matrix compatible with integrability. Since symmetry constraints do not fully determine its structure, we further exploit boundary Yangian symmetry, as the underlying algebraic structure, to derive a continuous family of integrable reflection matrices. A concrete realization of this framework arises in the study of operator insertions along the half-BPS Wilson loop in ABJM theory, which is holographically dual to type IIA string theory on AdS4 x CP3. In this setting, the boundary degree of freedom can be interpreted as a boundary bound state, emerging from pole structures in the dressing phase of the reflection matrix. We further analyze these states using the boundary bootstrap approach and find agreement with our construction. Finally, the ABJM realization allows for non-trivial perturbative checks of our proposal. The ultimate goal is to compute the Lüscher-type finite-size corrections to the energy spectrum, which are essential for determining the anomalous dimensions of short-chain operators, such as those appearing in deformations of Wilson loops in the ABJM model.  Our results, exploiting integrable structures in superconformal field theories, contribute to the broader program of understanding deformations and RG flows on line-defects in the AdS/CFT context. 

Quantum corrections to the tension of gravitational solitons near-criticality

Cielo Ramirez de Arellano

We show that the Gravitational Path Integral (GPI) at one-loop order permits the computation of a quantum correction to the tension of a near-critical gravitational soliton. First, we study an asymptotically, locally AdS4 soliton with AdS22×S1  asymptotics and an AdS2×R2 geometry near the origin. At criticality, the near-origin  geometry takes the form of a AdS2×H2 geometry.The one-loop partition function of pure gravity is dominated by tensor modes coming from large diffeomorphisms living near the origin.These modes produce a correction to the GPI that is logarithmic on  the parameter controlling the departure from criticallity. Next, we provide numerical evidence supporting the validity of extending these corrections to the full geometry by studying the eigenvalues of the Lichnerowicz operator on the near-critical case for the full geometry. Finally we explore an extension of these results to a supersymmetric 1/2-BPS charged soliton of N=2 SUGRA.

Pair production in charged black holes and CFT correlators

Cristian Andres Rivera Medina

We study the phenomenon of pair production in near-extremal charged black holes. Exploiting the enhanced symmetries and structure of the equations of motion, we map the problem to the computation of semiclassical correlation functions in Liouville Theory via the AGT Correspondence. Connections with recent developments involving effective actions and gravitational path integrals for near-extremal black holes will also be discussed.

Liouville strings in AdS3: the worldsheet story

Pedro Schmied

The worldsheet σ-model of strings on AdS3 with NS-NS fluxes can be equivalently described in terms of a Liouville field theory coupled to a timelike field with background charge, plus a marginal deformation. The operator that produces the deformation is non-normalizable and, from the string theory perspective, is associated to the spectral flow sector ω= 2. Its role is to control the winding number violation in scattering amplitudes. In the semiclassical (large k) limit, the central charge of the Liouville factor tends to that of the dual CFT2, namely c≃6k. This may appear very similar to what occurs in the Liouville-type description of the dual deformed orbifold CFT2, where a twist-2 deformation operator dressed with a non-normalized field also appears. Indeed, there are some similarities to that; however, there are also significant differences, which we discuss.

Ladder Operators and Fermionic Tensor Fields on Maximally Symmetric Spaces 

Matías Sempé

We construct ladder operators for fermionic fields of spin-1/2 and 3/2 relating distinct discretely labeled unitary irreducible representations of Spin(N+1)  on S^N and Spin(N,1) on dS_N. This is achieved by relying on the conformal killing vectors of these maximally symmetric spaces.

Clines and the analytic structure of black hole perturbations

Fernando Temoche

We revisit black hole perturbations through Heun differential equations, focusing on Frobenius power-series solutions near regular singularities and their connection formulas. Central to our approach is the notion of a cline in the complex plane, which organizes singular points of the differential equations and remain invariant under Möbius transformations. Building on the cline structure we identified in black hole horizons, we carry out a systematic reduction and relocation of poles in the differential equation to obtain explicit representations of the solutions. We illustrate our approach by extracting the scalar perturbation solutions for the 7-dimensional Myers-Perry black hole and deriving the static scalar tidal Love numbers. These results suggest that clines expose a Möbius-invariant order within black hole perturbations, rendering black hole perturbation problems remarkably tractable.

A new perspective on the dynamical stability of the AdS soliton

Monserrat Aguayo

The analysis of gravitational perturbations of asymptotically AdS spacetimes provides a useful tool for computing the spectrum of strongly coupled gauge theories via the AdS/CFT correspondence. In this context, the AdS soliton is dual to confining gauge theories, and its normal mode spectrum corresponds to the masses of glueball states in the boundary theory. Since this spacetime is Petrov type D, we revisit gravitational perturbations of the AdS soliton in 4 dimensions using the Teukolsky equations, extending this framework -usually applied to black holes- to spacetimes without a horizon. We have successfully reproduced the known normal mode spectrum obtained through alternative methods for the axial modes, providing a consistency check and supporting the validity of our computation. Meanwhile, the study of polar modes presents additional challenges. These results constitute a first step towards a Teukolsky-based description of the AdS soliton and suggest a new way to study glueball spectra in holographic confining backgrounds.

Logarithmic Corrections to Near-Extremal Black Holes in Einstein–Gauss–Bonnet Gravity

Alejandro Alvarado-Corzo

Quantum effects modify the thermodynamic properties of black holes beyond the classical Bekenstein–Hawking description. In this talk, I will discuss the origin of logarithmic corrections to the entropy and partition function of charged near-extremal black holes in five-dimensional Einstein–Gauss–Bonnet gravity. I will explain how the near-horizon geometry, one-loop fluctuations, and zero modes contribute to the low-temperature behavior of the system. The goal is to illustrate how higher-curvature interactions affect the quantum thermodynamics of near-extremal black holes and to identify which features remain universal beyond Einstein gravity.

Holographic Weyl Anomaly and Kounterterms in AdS Gravity

Jahaira Rosita Bonifacio Chavez

In this work, we derive contributions to the holographic Weyl anomaly of CFT_{d=2n} living on the boundary of asymptotically locally AdS_{D=2n+1} spacetimes. For this purpose, we employ the Kounterterms regularization scheme, which has the advantage of admitting a closed-form expression valid in arbitrary dimensions, in contrast to the counterterms used in standard holographic renormalization, whose full series is not known. However, it is important to note that this scheme exhibits discrepancies with respect to the standard counterterm approach. These differences imply that the Einstein--Hilbert action supplemented with Kounterterms, as well as its variation, still contain divergences. Nevertheless, the holographic Weyl anomaly can be correctly extracted if we isolate only the finite contribution of the variation of the action, obtained through an asymptotic analysis combined with power-counting arguments. This procedure allows us to obtain some closed-form expressions that contribute to the Weyl anomaly in arbitrary even dimensions d = 2n. In this way, we identify a quantity that correctly reproduces the Type A anomaly, given by the Euler density and its associated central charge, as well as quantities that contribute to the Type B anomaly. These include terms such as the Pfaffian of the Weyl tensor with its corresponding coefficient, and terms constructed from contractions of the Weyl tensor with the Schouten tensor, which form part of conformal invariants. Additionally, there exist other contributions that complete the formation of the conformal invariants, whose form must be determined through a case-by-case analysis.

Capacity of entanglement in RST gravity

Daniel Fondevila

We aim to understand information dynamics around the Page time in evaporating black holes with semiclassical gravity computations. We study whether the topological phase transition in the replica partition function used to compute entanglement entropy (first cumulant of the density matrix) in 2D dilatonic gravity can be captured by the capacity of entanglement (second cumulant of the density matrix). In RST gravity, we compute the CoE in the two-interval configuration, and it jumps around the Page time and then diverges with the volume of the black hole interior.

Cylindrical Renormalization and Brown–York Mass in Melvin and Schwarzschild–Melvin Spacetimes

Alessandro Huaman

We study the Euclidean action and Brown–York quasilocal mass of the Melvin and Schwarzschild–Melvin geometries in four-dimensional Einstein–Maxwell theory. Since these spacetimes do not exhibit the usual spherically asymptotically flat behavior, we introduce a cylindrical regularization scheme adapted to the magnetic axis.  The boundary is placed at a fixed cylindrical radius, while the longitudinal interval is scaled with the radial cutoff. A sequential limiting procedure is then employed to preserve the cylindrical structure of the asymptotic region. Within this framework, we show that the standard Mann–Marolf-type counterterm does not remove the relevant divergences. We instead propose a local boundary counterterm constructed from the norm of the axial Killing vector, which captures the asymptotic behavior of the azimuthal circumference.  This prescription cancels the leading divergences without requiring background subtraction. The renormalized Euclidean action and Brown–York mass both vanish for the pure Melvin universe.  For the Schwarzschild–Melvin geometry, the Euclidean action is one half of the product of the inverse temperature and the black-hole mass parameter, while the Brown–York mass equals the mass parameter. These results identify the Melvin universe as a zero-mass magnetic reference and show that the finite black-hole mass is preserved after cylindrical renormalization.

Dirac–Bergmann algorithm and canonical quantization of k-essence cosmology

Andrés Lueiza Colipí 

We develop a general canonical quantization scheme for k-essence cosmology in scalar–tensor theory. Utilizing the Dirac–Bergmann algorithm, we construct the Hamiltonian associated with the cosmological field equations and identify the first- and second-class constraints. The introduction of appropriate canonically conjugate variables with respect to Dirac brackets, allows for the canonical quantization of the model. In these new variables, the Hamiltonian constraint reduces to a quadratic function with no potential term. Its quantum realization leads to a Wheeler–DeWitt equation reminiscent of the massless Klein–Gordon case. As an illustrative example, we consider the action of a tachyonic field and investigate the conditions under which a phantom crossing can occur as a quantum tunneling effect. For the simplified constant potential case, we investigate the consequences of different boundary conditions on the singularity avoidance and to the mean expansion rate.

A Carrollian landscape of NSNS supergravity

Sergio Patiño

We study the ultra-relativistic limit of the bosonic NSNS sector of supergravity. By introducing suitable Carrollian expansions for the metric, Kalb–Ramond field, and dilaton, we obtain a finite action describing the dynamics of the resulting non-Lorentzian fields. The finite part of the relativistic Levi–Civita connection naturally defines a Carrollian affine connection and its associated geometric structure. The resulting theory provides a covariant Carrollian formulation of the NSNS sector and a possible spacetime framework for the effective description of Carrollian strings.

Dissipation in Open Holographic Systems and Optical Depth Law for AdS-BTZ Open Holography

Ignacio Quiroz Vargas

Open holography consists of coupling a quantum field theory to a holographic bath and analyzing the resulting system. Often, this is done by introducing a double trace coupling while preserving the full unitary dynamics of the system and bath. Here, we trace out the bath and derive analytical expressions for the dissipation it produces on the system. We analyze different AdS–BTZ, BTZ–BTZ, and spinning BTZ–AdS configurations and find that this procedure has several advantages: (1) it yields fully analytical expressions for the quasinormal modes after the bath has been traced out; and (2) by tracing out the bath and then reversing the roles of the system and bath, the full quasinormal-mode spectrum can be analytically reproduced in the weak-coupling regime, whereas previous numerical computations often took several hours or days. Additionally, for the general AdS–BTZ system, we derive a non-perturbative analytical expression in the UV, or high-n modes, regime that takes the same form as an optical depth law in optics. Therefore, in the UV, the open holographic system can be reinterpreted as a non-unitary scattering problem where the holographic interface in the weak coupling regime is characterized by the transmission coefficient obtained from transparent boundary conditions, which depends only on the coupling and the dimension of the operator without referencing details of the bath. We call this new quantity c_optical, and expect that the dissipation of more general systems can be characterized by this quantity.

Nonlinear Perturbations in Holographic Transport Phenomena 

Vitor Silva

In this presentation, we investigate the dynamics of fermionic operators in the presence of a perturbed gauge field within the framework of the AdS/CFT correspondence. Using a bottom-up holographic approach, we introduce α' F^4 corrections to the gauge field dynamics and solve the corresponding equations of motion numerically as functions of the perturbation parameter α', the system charge q, and the temperature-related parameter β. The resulting gauge field solutions are then treated as background fields for the fermionic sector, allowing us to study their influence on the retarded Green’s function through numerical analysis. Our results reveal novel features in the conductivity, including attenuation effects and the emergence of instabilities induced by variations in α', q, and β. In addition, we identify indications of a possible second-order phase transition, which will be further discussed during the presentation.

Regular geometries from singular matter in modified gravity

Aitor Vicente-Cano

It has recently been shown that the Schwarzschild singularity is generically resolved by the introduction of infinite towers of higher-curvature corrections to the Einstein-Hilbert action. In such theories, matter collapse leads to the formation of regular black holes. In this talk, I will present how minimally coupled matter spoils Markov's limiting curvature hypothesis, which is satisfied by vacuum solutions. While mildly singular matter yields curvature singularities, sufficiently singular matter distributions paradoxically restore regularity. I will therefore argue that a consistent picture entails the inclusion of non-minimally coupled matter terms.