2026 Simons Collaboration on Celestial Holography Annual Meeting

The Simons Collaboration on Celestial Holography annual meeting took place April 16–17, 2026, following a two-day satellite meeting at the Andaz Hotel. There were 121 participants, including collaboration PIs, postdocs, and graduate students, as well as a number of external and affiliated faculty. The meeting included four review talks from collaboration PIs, summarizing progress and explicating interconnected results in bottom-up and top-down approaches, scattering amplitudes, asymptotic symmetries and canonical gravity, and twistorial methods. There were also three research talks from affiliated faculty and a poster session held by collaboration graduate students.

There is a large, evolving tapestry of ideas in high energy physics that the collaboration inspired. Collaboration Director Andrew Strominger kicked off the meeting and highlighted notable results, many of which emerged in the previous six months. The collaboration has been a nexus of inspiration for numerous adjacent approaches, which have recently expanded to include AI and the conformal bootstrap. Strominger noted new formulas for all-multiplicity one-minus amplitudes, which emerged from collaboration with OpenAI (PIs Strominger, Skinner), as well as two-loop all-multiplicity results for all-plus amplitudes in massless QCD, which emerged from the chiral algebra bootstrap. Recently, asymptotic soft theorems have been applied to derive Ward identities for in-in energy correlators, which are observed at detectors; this, one of the first mergers between celestial holographic and conformal bootstrap methods, produced new results for the collider physics community (PI Pasterski). In addition, Strominger reviewed new deformations of the Lw_(1+∞)-algebra (PIs Mason, Taylor) valid in both AdS/dS spacetimes. It is remarkable that such infinite dimensional algebraic structures are not merely an artifact of flat spacetimes, and moreover admit a universal manifestation in light-ray operators of three-dimensional CFTs via AdS/CFT (PI Strominger). Universal light-ray operators in 4d Lorentzian CFTs also carry a representation of Lw_(1+∞) (PI Pate). This algebra, and its gauge theoretic analogue, were given special attention in the review talks by PIs Freidel, Mason, who derived their appearance from canonical gravity methods and twistor geometry, as well as how to link these seemingly disparate perspectives together. Freidel also discovered a novel bulk formulation of these symmetries in terms of 1-form operators developed in the field of generalized symmetries. PI Puhm extended the discussion of soft theorems beyond tree-level, describing a new infinite set of logarithmic soft theorems associated to quantum effects. PI Costello reviewed how such algebraic structures constrain and compute 4d form factors, analogous to the famous Yangian quantum group in integrability. Topics reviewed including the recent determination of nonlinear deformations to all-loop order in perturbation theory (PI Paquette) and his own work incorporating nonperturbative deformations from 4d instantons.

There were also three research talks, describing new works informed by the Collaboration’s approaches, goals, and results. Alday studied the appearance of soft factors in planar 4d N=4 super Yang–Mills. Although this theory has been tremendously well-studied, Alday used the dual pentagonal Wilson loop representation of amplitudes to study the soft physics captured by the collinear limit. Sleight showed how radiative observables in flat and de Sitter spacetimes can be probed using Euclidean AdS as a starting point, a setting with very well-developed computational technology. Finally, Takayanagi discussed an alternative construction of flat space holography by arranging end of the world branes in the AdS/BCFT framework. The resulting dual theory of this construction is a codimension-1 Carrollian CFT. His construction leads to a very large novel family of flat space duals which can be probed with informational theoretic observables like entanglement entropy, in particular adapting the prescription of W. Song discussed in last year’s annual meeting.

Fernando Alday
University of Oxford

On the Soft Behaviour of N=4 SYM
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Over the last decades, various tools have been developed to compute scattering amplitudes in planar N=4 SYM, to all loops in perturbation theory, at strong coupling, and even non-perturbatively. We use some of these tools to understand the soft behaviour of planar N=4 SYM.
 

Kevin Costello
Perimeter Institute for Theoretical Physics

Celestial Chiral Algebras, Amplitudes, and Holography
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Kevin Costello will review progress on the quantized vertex algebras controlling form factors of self-dual gauge theory and how they are useful for computing amplitudes.
 

Laurent Freidel
Perimeter Institute for Theoretical Physics

Noether Perspective on the Higher Spin Symmetry in Gravity and Yang–Mills
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In this talk, Laurent Freidel will review some of the progress made over the past four years in our understanding of the symmetries governing the tower of subleading soft theorems in gravity and Yang–Mills. Freidel will show how the Noetherian realization of these symmetries connects the soft celestial perspective and the hard Carrollian one. In particular, we will see how the charges are realized in the asymptotic phase space via light-ray operators and how the rich algebraic structure governing colinear singularities is encoded in the Noetherian perspective. Feidel will show how this foundational understanding of asymptotic symmetry has shed light on the possibility of labelling states by a discrete basis, given a new understanding of large gauge transformations, and infused new developments in the Carrollian geometry of finite null surfaces. Freidel will then explain some of the deep connections this perspective has with Twistor geometry when applied to the self-dual case, and how it involves a notion of higher-form symmetries developed in condensed matter. If time permits, he will comment on recent developments related to the log-soft theorem and prospective directions.
 

Lionel Mason
University of Oxford

Three Perspectives on the Origins of Celestial Charges
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Celestial charges play a central role in celestial holography; they arise from the algebra of soft limits of amplitudes and are understood as defining OPEs in celestial CFTs for both gauge and gravity theories. They have been obtained from charge aspects on space-time at null infinity, Noether charges for geometric symmetries on twistor space and from twisted holography. This talk will draw together these origin stories and explain how the symmetries can be understood as the generalized symmetries for the self-dual sectors of the theories geometrically realized locally on twistor space, but ‘hidden’ on space-time. The charge aspects have a Noetheriean origin in twistor space that can be ‘Penrose-transformed’ to give space-time charge aspects on the one hand and related to the twisted holography celestial CFT via an extrapolate dictionary. If there is time, quasi-local extensions will be discussed. This is based on joint work with Adam Kmec, Romain Ruzziconi and Atul Sharma.
 

Andrea Puhm
University of Amsterdam

Long-Range Interactions in Celestial CFT
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Loop corrections in QED and gravity have recently been conjectured to give rise to an infinite tower of logarithmic soft theorems governing the universal low-energy behavior of photons and gravitons. Andrea Puhm will discuss the implications of this tower for celestial CFT and for the algebra of conformally soft operators. The symmetry-governed part of the tower of logarithmic soft factors turns out to exponentiate and gives rise to Ward identities that exhibit characteristic non-local behaviors which reflect the pair-wise interactions between hard operator insertions mediated by gauge bosons. Puhm will define conformally soft tree and loop operators, and compute their operator product expansions (OPE) on the celestial sphere from the consecutive double soft limit. This method presents an alternative to the collinear limit of bulk scattering amplitudes which has been used to compute the singluar part of hard and soft OPEs at tree-level. Andrea will comment on the implications of these results for the celestial symmetry algebra.
 

Charlotte Sleight
University of Naples Federico II

Holograms in the Sky from Euclidean AdS
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In this talk, Charlotte Sleight will discuss how lessons from AdS/CFT can be extended to de Sitter and Minkowski space. A key hurdle for holography in these settings is the presence of outgoing radiation. Recent results show that observables at de Sitter future infinity and on the celestial sphere of Minkowski space can nevertheless be expressed as boundary correlators in Euclidean AdS. This Euclidean perspective provides a concrete bridge between radiative observables and familiar AdS technology, and helps clarify which structural features of AdS/CFT persist and which require modification when one moves beyond the AdS setting.
 

Andrew Strominger
Harvard University

Celestial Holography: Past, Present, and Future
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An overview will be given of past results, current research, and future prospects for celestial holography.
 

Tadashi Takayanagi
Kyoto University

Flat Space Holography via AdS/BCFT
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In this talk, Tadashi Takayanagi will discuss a new class of AdS/BCFT setups, where the world volumes of end-of-the-world branes (EOW branes) are given by flat spaces, to explore flat space holography from an AdS bulk. Takayanagi will show that the new setups provide gravity duals of CFTs in the presence of null boundaries and that holographic calculations lead to new predictions on entanglement entropy, correlation functions, and partition functions for CFTs with null boundaries. By considering a bulk region between two EOW branes, Takayanagi will present an AdS/BCFT explanation that the flat space gravity is dual to a Carrollian CFT (CCFT), including the swing surface calculation of entanglement entropy.

Watch a playlist of all presentations from this meeting here.