Microscopic models of Cosmology: The case of (A)dS₂ I will describe some recent progress in developing microscopic models of two-dimensional cosmologies, emphasizing which desired characteristics they should possess. Then I will focus in the two-dimensional gravitational (compact) Sine-Gordon model that contains (A)dS₂ as well as more complicated wineglass and oscillatory wormhole saddles. This model admits a putative microscopic normal matrix model description that allows an in principle non-perturbative description of the physics. I will discuss some recent progress towards establishing and developing this duality.

Flat from AdS, for any spin, and in any dimension The spaces of solutions to the equations of motion of generic gauge theories, including gravity and higher-spin theories, look very different depending on whether the background is flat or (A)dS. Even so, we will show how the solutions of the linearized equations of motion for fields of any spin in Minkowski space can be obtained as a limit of the corresponding solutions in AdS in any even space-time dimension. We will also discuss how this flat-space limit reflects itself in the Flato Fronsdal theorem, which is a cornerstone of higher-spin holography in AdS.

Unitary Rigid Supersymmetry for the Chiral Graviton and Chiral Gravitino in de Sitter Spacetime It is commonly believed that a unitary supersymmetric quantum field theory (QFT) involving graviton and gravitino fields on fixed 4-dimensional de Sitter spacetime (dS4 ) cannot exist due to known challenges associated with supersymmetry (SUSY) on spaces with positive cosmological constant. In this talk, we contradict this expectation by presenting a new unitary supersymmetric QFT on fixed dS4 : the free supersymmetric theory of the chiral graviton and chiral gravitino fields. The theory overcomes the known obstacles to unitary global SUSY on de Sitter because the commutator between two SUSY transformations closes on the conformal algebra so(4,2) rather than the de Sitter algebra so(4,1). Crucially, the so(4,2) symmetry is realised through unconventional conformal-like transformations. Based on joint work with Atsushi Higuchi: https://arxiv.org/abs/2503.04515

An inflationary cosmology from Anti-de-Sitter wormholes There are various proposals as to what initial state can give rise to an inflationary cosmology. The two most popular ones are the no boundary (Hartle-Hawking) and the tunneling (Vilenkin) proposals. Both of them explain only part of the observations and lead to some paradoxes. I will review these proposals and I will propose a novel initial state (wavefunction) of the universe which in the far past has asymptotically AdS boundary conditions. In the semiclassical limit it is a Euclidean wormhole solution that can give rise to an expanding universe upon analytic continuation to Lorentzian signature. This proposal evades some of the issues that plagued the no boundary and the tunneling proposals. Moreover, the asymptotic AdS conditions in the Euclidean past could in principle allow for the description of inflationary cosmologies and their perturbations within the context of holography, leading to microscopic models.

Quantizing Carrollian Field Theories Carrollian field theories have recently emerged as a candidate dual to flat space quantum gravity. In this talk, I will discuss the quantization of generic two-derivative electric and magnetic Carrollian theories, highlighting some of the subtleties involved in this process.
As another concrete application, I will discuss the quantization of a two-dimensional BMS3-invariant field theory, which captures the boundary degrees of freedom of three-dimensional flat space gravity.
I will conclude with potential lessons for the program of flat space holography from the carrollian point of view.

Non-perturbative construction of the de Sitter boundary In this talk, I will review some of the recent progress in non-perturbative quantum field theory in de Sitter such as Kallen-Lehmann and partial wave expansion. I will start by explaining why we are interested in de Sitter and pointing out some of the differences and similarities between anti-de Sitter and de Sitter spacetimes. With the goal of bootstrapping de Sitter's conformal boundary, I will propose a de Sitter-specific bulk-to-boundary expansion, with a continuous family of boundary operators. In the end, I will derive an inversion formula for the bulk-to-boundary expansion, where, given a bulk theory, the boundary operator content is constructed as an integral of the bulk operator times the bulk-to-boundary propagator. These boundary operators exhibit two-point functions that include contact terms alongside standard CFT two-point functions.

Celestial holography from EAdS space We analyse the framework of Celestial holography through the lens of group theory, developing a systematic approach based on Euclidean AdS correlators as fundamental building blocks. These correlators are intrinsically tied to a non-flat foliation of Minkowski spacetime—referred to as the hyperbolic foliation—in which the spacetime is foliated into Euclidean AdS (EAdS) slices inside the light cone and dS slices outside. Employing this foliation, we demonstrate that each contribution to massive Celestial correlators can be reformulated as a linear combination of contributions to corresponding massive Witten correlators in EAdS. We explicitly establish this result for both contact diagrams and the four-point exchange diagram in Celestial holography, and it potentially extends to all orders in perturbation theory by leveraging the bootstrapping properties of the Celestial CFT.

QFT in AdS Putting strongly coupled Quantum Field Theories on a rigid Anti-de Sitter background can provide considerable advantages with respect to flat space, a feature first realized by Callan and Wilczek (1989). Such background cures infrared divergences in a way that does not forbid spontaneous symmetry breaking or phase transitions. Moreover, it contains as a natural subsector asymptotic observables which behave like correlators in a conformal theory. The latter feature provides powerful tools to analyze such theories. In this discussion session, I will review this construction and apply it to the foremost example of strongly coupled theories, that is Yang-Mills theories in four spacetime dimensions, both without and with matter. Such approach allows to study the problem of confinement in a more controlled scenario, phrasing it as statement about the (non) existence of certain boundary conditions in the flat space limit. We will also discuss the implications for the endpoint of the conformal window in the presence of matter.

Non-linear asymptotic symmetries in warped AdS3 holography Abstract

Features of the Partition Function of a Λ > 0 Universe Abstract

Momentum space Carrollian correlators and Carrollian dual to massive flat scattering Abstract

Spin-1 Fields in AdS Abstract

Reconstruction of Bulk Operators via Petz Map Abstract

Unimodular Jackiw-Teitelboim gravity and de Sitter quantum cosmology Abstract

Subleading soft dressings of asymptotic states in explicit QED processes Abstract