Next meetings
TBD, Francesca Mariani (UGent): Introduction to JT gravity and its applications to near-horizon region of near-extremal black holes (NO6 classroom).
Abstract TBA.
25.04.2025, Dima Fontaine: An overview of plane wave spacetimes (NO6 classroom).
Plane wave spacetimes are simple geometries that allow for a null, covariantly-constant Killing vector. First introduced as models of gravitational radiation, the last 30-odd years have shown that these spacetimes have a role to play in string theory and holography — AdS, or Carroll! In this talk, I will introduce what plane waves are and what is so interesting about them. On the menu: an exact test of the AdS/CFT correspondence, quasinormal modes and photon ring holography, strange conformal boundaries and some of my work on holographic duals to conformal Carroll field theories.
Past meetings
28.02.2025, Maria Knysh (VUB): Semi-classical black hole microstates (NO6 classroom).
In this talk, I will review the construction of an infinite family of microstates for eternal black holes in general relativity with a negative cosmological constant. These states, which contain shells of matter behind the horizon, are an overcomplete basis of the black hole Hilbert space and offer a new avenue to address long-standing puzzles. The focus will be on two applications: first, their role in establishing the factorization of the Hilbert space of eternal black holes, and second, their relevance for studying out-of-equilibrium eternal black holes. I will conclude by outlining some open problems that this framework now allows us to approach.
29.11.2024, Loïc Honet: Introduction to category theory (NO6 classroom).
Have you ever noticed any similarities between the definitions of homeomorphisms and diffeomorphisms? Between the construction of the Cartesian product and the disjoint union of sets? Or even between pullbacks and pushforwards? The short answer to these questions is: category theory. In this brief invitation to category theory, we will explore the core concepts that unify the languages of diverse fields, spanning Mathematics, Physics, Computer Science, and even Philosophy. Beginning with the basic notion of categories, we will examine concepts such as products, coproducts and their universal arrow properties. This short mathematical endeavour will guide us in reformulating key concepts in Mathematics, such as Clifford Algebras and group representation theory, through the framework of categories and functoriality.
14.10.2025, Marc Henneaux (International Solvay Institutes, Collège de France): Carroll-invariant field theories and spacetime subsystem symmetries (NO6 classroom).
07.06.2024, Thomas Smoes: Gauge theories as constrained Hamiltonian systems (from 'Quantization of Gauge Systems', Henneaux-Teitelboim) (NO6 classroom)
The aim of this presentation is to give an introduction to the classical analysis of gauge theories performed by Dirac (Generalized Hamiltonian Dynamics, 1950). In gauge theories, the general solution of the equations of motion contains arbitrary functions of time. This arbitrariness implies that the canonical variables are not all independent and, thus, that a gauge system is always a constrained Hamiltonian system. We will discuss how the so-called first-class constraints generate the gauge transformations and how the so-called second-class constraints can be set equal to zero after introducing the Dirac bracket.
31.05.2024, Wendi Tan: The Infrared Triangle (NO6 classroom)
Proposed by A. Strominger, infrared triangle is a triangular equivalence relation among asymptotic symmetries, soft theorems and memory effects of field theories with massless particles. It can be considered as part of the burgeon of celestial holography and carrollian holography in a sense. We will see this triangular equivalence relation in two examples, namely large U(1) gauge symmetries-soft photon theorem-electromagnetic memory and BMS supertranslations-leading soft graviton theorem-displacement memory effect, with the setting of coordinates, boundary conditions and phase space.
10.05.2024, Louan Mol: Quiver gauge theories, Geometry and Dualities
String theory provides a natural correspondence between a special class of supersymmetric gauge theories called "quiver gauge theories" and a special class of geometric spaces called "Calabi-Yau orbifolds". After having introduced the basic notions of both sides of this correspondence, we will discuss the correspondence per se and its limitations. This will be natural segway to discuss dualities and their geometric interpretation.
26.04.2024, José Figueroa: Covariant phase space formalism with boundaries (arXiv:1906.08616)
The goal is to present the Covariant Phase Space formalism, which allows us to obtain the canonical conserved quantities of a physical system (i.e. the Hamiltonian generators) in a covariant way, which is particularly useful for gauge theories. The formalism was originally developed by Wald and co., and recently reviewed by Harlow and Wu where they emphasize the crucial role of boundary terms and having a well-defined action principle. This solves some ambiguities previously found when obtaining the conserved charges.
12.04.2024, Dima Fontaine: Inonu-Wigner contractions
Galilean transformations are the non-relativistic limit of Poincaré transformations. As such, this limit should also manifest at the level of the algebra. Defining this limiting process leads to the definition of group contraction, as proposed by Inonu and Wigner in the 50’s. I will discuss the original developments of Inonu and Wigner and derive the Inonu-Wigner contraction theorem that sets the conditions for such a limit to be taken, then show a few examples.