Celestial meets de Sitter holography

16 Jun 2025, 09:00 → 20 Jun 2025, 22:00 Europe/Rome

Villa Orlandi, Capri

Charlotte Sleight (Istituto Nazionale di Fisica Nucleare), Massimo Taronna (Federico II), Tomasz Taylor

Invited Participants 

Luis Fernando Alday (Oxford)

Dionysios Anninos (KCL)

Tarek Anous (Queen Mary U.)

Glenn Barnich (ULB)

Paolo Benincasa (Santiago de Compostela U.)

Ernesto Bianchi (Southampton U.)

John Joseph Carrasco (Northwestern U.)

Geoffrey Compère (ULB)

Jordan Cotler (Harvard U.)

Frederik Denef (Columbia U.)

Damián Galante (KCL)

Diego Hofman (Amsterdam U.)

Austin Joyce (Chicago U.)

Lionel Mason (Oxford U.)

Ugo Moschella (Insubria U.)

Benjamin Pethybridge (KCL)

Guilherme Pimentel (SNS Pisa)

Daniele Pranzetti (Udine U.)

Andrea Puhm (Amsterdam U.)

Ana-Maria Raclariu (KCL)

Alan Rios Fukelman (KCL)

Kostas Skenderis (Southampton U.)

David Skinner (Cambridge. U.)

Stephan Stieberger (MPI Munich)

Andrew Strominger (Harvard U.)

Bin Zhu (Edinburgh U.)

 

Organising Committee 

 

Charlotte Sleight (Naples U. & INFN)

Massimo Taronna (Naples U. & INFN)

Tomasz Taylor (Northeastern U.)

 

Meeting poster.pdf

Monday, 16 June

Registration

Welcome

Review: Flat space holography (part 1)

1 Flat space holography (part 1)

I will review recent developments in flat space holography with a focus on connections to (A)dS/CFT. Topics I will discuss include new insights into celestial holography building on``The holographic reduction of Minkowski space-time’’ by de Boer and Solodukhin, recovering Carrollian/celestial holography from a flat space limit of AdS/CFT, and deformations of the celestial chiral algebras in the presence of a cosmological constant.

Speaker: Ana-Maria Raclariu

Coffee break

Review: Flat space holography (part 2)

2 Flat space holography (part 2)

I will review recent developments in flat space holography with a focus on connections to (A)dS/CFT. Topics I will discuss include new insights into celestial holography building on``The holographic reduction of Minkowski space-time’’ by de Boer and Solodukhin, recovering Carrollian/celestial holography from a flat space limit of AdS/CFT, and deformations of the celestial chiral algebras in the presence of a cosmological constant.

Speaker: Ana-Maria Raclariu

Lunch break

Topical Seminars: Flat space holography (part 1)

3 Celestial CFT data: w-(1+infty) and beyond

Speaker: Andrea Puhm

4 High-energy string theory and celestial holography

In my talk I make connection between two seemingly unrelated topics: (a) the high energy limit of string theory (more specifically, the high energy (zero tension) limit of tree-level string scattering in flat backgrounds) and its subleading corrections as saddle-point approximation on the string world-sheet, (b) the infinite energy limit of celestial string amplitudes as stationary phase approximation. We shall give evidence of a connection of the string world-sheet and the celestial sphere of the underlying scattering process.

Speaker: Stephan Stieberger

Coffee break

Topical Seminars: Flat space holography (part 2)

5 Soft Algebras in AdS4 and dS4

Speaker: Andrew Strominger

6 Carrollian Amplitudes and Holographic Correlators in AdS3/CFT2

With the new notions of flat holography introduced in recent years, there has been increased interest in relating the new formalisms to the flat space limit of AdS/CFT. We study Carrollian amplitudes of massless scalars in (1+2) Minkowski space. Using the prescription recently shown by Alday et al. [1] originally designed for the AdS4 Witten diagrams, we show that AdS3 Witten diagrams in position space in the flat space limit reduce to Carrollian amplitudes. The flat space limit in the bulk is implemented by the Carrollian limit at the boundary. Focusing on four-point correlators with contact and exchange diagrams, we show that the Carrollian limit makes the universality of the bulk point singularity manifest upon performing analytic continuation to the Lorentzian signature of the boundary correlators. Unlike four-point Carrollian amplitudes in (1+3) dimensions, the (1+2) dimensional ones are non-distributional, having analytic properties simpler than the AdS correlators. We also observe for the first time a double copy structure of Carrollian amplitudes.

Speaker: Bin Zhu

Organised dinner in Anacapri

Tuesday, 17 June

Review: de Sitter holography (part 1)

7 de Sitter holography (part 1)

Speaker: Dionysios Anninos

Coffee break

Review: de Sitter holography (part 2)

8 de Sitter holography (part 2)

Speaker: Dionysios Anninos

Lunch break

Topical Seminars: de Sitter holography (part 1)

9 Hartle-Hawking revisited

By leveraging recent insights on de Sitter holography from low-dimensional gravity, we study basic properties of the quantum mechanics of the Hartle-Hawking wavefunction in general dimensions. We highlight connections to basic puzzles in de Sitter quantum gravity.

Speaker: Jordan Cotler

10 Finite boundaries meet all-Lambda’s holography

I will describe recent progress in trying to understand the theory of general relativity in manifolds with finite boundaries and comment on possible holographic applications, in principle valid for any value of the cosmological constant.

Speaker: Damián Galante

Coffee break

Topical Seminars: de Sitter holography (part 2)

11 Insights from exact results in dS

In this talk I will present an exactly solvable theory on a fixed de Sitter spacetime that can be analyzed efficiently using Euclidean methods. I will then discuss the fully non-perturbative, all loop correlation function of gauge invariant operators and demonstrate many features endemic of quantum field theory in de Sitter space such as the appearance of late-time logarithm and their resummation. Time permitting, I will discuss how this theory allows us to entertain the idea of new de Sitter invariant vacuum states.

Speaker: Alan Rios Fukelman

12 TBA

Speaker: Tarek Anous

Wednesday, 18 June

Excursion: Boat tour around Capri island

Thursday, 19 June

Review: Holographic correlators in anti-de Sitter space (part 1)

13 Holographic correlators in anti-de Sitter space (part 1)

We will describe recent progress in the computation of string scattering amplitudes on AdS, reviewing first the story in flat space

Speaker: Luis Alday

Coffee break

Review: Holographic correlators in anti-de Sitter space (part 2)

14 Holographic correlators in anti-de Sitter space (part 2)

We will describe recent progress in the computation of string scattering amplitudes on AdS, reviewing first the story in flat space

Speaker: Luis Alday

Lunch break

Topical Seminars: Asymptotic symmetries and holography (part 1)

15 Infrared structure of gravitational scattering up to quadrupolar order

Asymptotically flat spacetimes have been defined from consistently matching their five infinities such that they share a single BMS group of asymptotic symmetries and associated charges. We propose a consistent subleading and subsubleading structure which is covariant under the BMS group. At subleading order, we identify three conservation laws: tails are conserved between past and future null infinity, an identity leading to the subleading soft graviton theorem holds, and a flux-balance law of super-Lorentz charges holds. At subsubleading order, we identify the flux-balance law of quadrupolar charges which we define for the first time in full general relativity. Moreover, two conservation laws of subleading tails hold, and two conservation laws hold which are related to the classical subsubleading soft graviton theorem and its logarithmic correction.

Speaker: Geoffrey Compère

16 (Anti-) de Sitter deformations of celestial symmetries and their twistor origin

This talk will review the twistor origins of celestial symmetry algebras and their deformations/extension to (A)dS. It will go on to discuss their origin as Hamiltonians via twistor actions and connections with the integral systems literature and top down approaches to celestial holography. This is partly based on joint work with Bittleston, Bogna, Kmec & Skinner arxiv:2403.18011 and with Kmec, Ruzziconi and Sharma arxiv:2506.01888.

Speaker: Lionel Mason

Coffee break

Topical Seminars: Asymptotic symmetries and holography (part 2)

17 On the mixed helicity sector of celestial symmetries

The mixed helicity sector of celestial symmetries has been largely unexplored so far. I will report on recent progress in expressing the mixed helicity charge bracket for gravity and YM theory in a closed form, revealing the key role played by the shadow transformation. The correspondence between the hard charge action on conformal primary fields and the celestial OPE provides consistency checks for, as well as new insights into, the inclusion of shadow operators in celestial CFT.

Speaker: Daniele Pranzetti

18 TBA

Speaker: David Skinner

Friday, 20 June

Review: Cosmological Correlators (part 1)

19 Cosmological Correlators (part 1)

Speaker: Kostas Skenderis

Coffee break

Review: Cosmological Correlators (part 2)

20 Cosmological Correlators (part 2)

Speaker: Kostas Skenderis

Lunch break

Topical Seminars: de Sitter QFT and cosmological correlators (part 1)

21 A geometrical picture for processes in expanding universes

I present a first principle definition of the Bunch-Davies
wavefunctional in perturbation theory for generic scalars in arbitrary
FRW cosmologies. This novel picture generalises the original
description of conformally-coupled and light states in terms of
(generalised) cosmological polytopes. I'll comment on the insights that
it provides on the analytic structure of such an observables, encoded
in its boundary structure

Speaker: Paolo Benincasa

22 TBA

Speaker: Austin Joyce

Coffee break

Topical Seminars: de Sitter QFT and cosmological correlators (part 2)

23 A few basic facts about de Sitter and Anti-de Sitter quantum field theory and some of their applications

A will discuss a general covariant approach to dS and AdS QFT based on plane waves and the global analyticity properties of the correlation functions. I will also sketch some recent results including the exact calculation of one and two-loop diagrams

Speaker: Ugo Moschella

24 Twistors and Spin in cosmology

I will describe how twistors are the natural language to describe massless particles with spin in de Sitter space, and illustrate the formalism with some examples.

Speaker: Guilherme Pimentel

Organised dinner in Anacapri