Dec. 15, 2025 – Dec. 19, 2025
9:30 AM – 5:00 PM
The St. Regis Hotel
34 Coot Pond Road, St.George’s GE 03, Bermuda
Fernando Alday, Nima Arkani-Hamed*, Roland Bittleston, Jan de Boer, Sangmin Choi, Kevin Costello*, Jordan Cotler*, Laurent Freidel*, Lucia Gomez-Cordova, Alfredo Guevara, Kelian Häring, Mina Himwich, Lionel Mason*, Walker Melton, Prahar Mitra, Anthony Morales, Natalie Paquette*, Sabrina Pasterski*, Monica Pate*, Andrea Puhm*, Ana-Maria Raclariu, Charlotte Sleight, David Skinner*, Andy Strominger*, Massimo Taronna, Tom Taylor*
*Collaboration PIs
Apr. 14, 2026 – Apr. 15, 2026
9:30 AM – 5:30 PM
Andaz 5th Avenue
485 5th Avenue, New York, NY 10017
Apr. 16, 2025 – Apr. 17, 2025
Thursday: 8:30 AM – 5 PM
Friday: 8:30 AM – 2 PM
Gerald D. Fischbach Auditorium
160 5th Avenue, New York, NY 10010
Speakers:
Fernando Alday, University of Oxford
Kevin Costello, Perimeter Institute for Theoretical Physics
Laurent Freidel, Perimeter Institute for Theoretical Physics
Lionel Mason, University of Oxford
Andrea Puhm, Ecole Polytechnique
Charlotte Sleight, University of Naples
Andrew Strominger, Harvard University
Tadashi Takayanagi, Kyoto University
Meeting Goals:
A central goal of the Simons Collaboration on Celestial Holography is to find realizations of the holographic principle for quantum gravity in (nearly) flat spacetimes like the one we inhabit. The collaboration employs both top-down approaches guided by string and twistor theory and bottom-up approaches guided by soft theorems and asymptotic symmetries.
The 2026 annual meeting will bring together a wide range of theoretical physicists and mathematicians working on disparate topics relevant to this endeavor as well as observers pursuing detection of the associated memory effects. Speakers will review the foundations of the subject, present recent developments and explore future research focus areas.
Jul. 7, 2025 – Jul. 11, 2025
St Anthony’s College
62 Woodstock Road, Oxford OX2 6JF
Speakers:
Tim Adamo*, University of Edinburgh
Bernardo Araneda, Max Planck Institute
Lydia Bieri, University of Michigan
Jordan Cotler*, Harvard University
Maciej Dunajski, University of Cambridge
Laurent Freidel*, Perimeter Institute
Adam Kmec, University of Oxford
Silvia Nagy, Durham University
Roger Penrose
Andrea Puhm*, University of Amsterdam
David Skinner*, University of Cambridge
Zhenya Skvortsov
Andy Strominger*, Harvard University
Robert Wald, University of Chicago
Meeting Goals:
Celestial holography has drawn together ideas from conventional AdS/CFT holography with studies of flat space asymptotics at null infinity, asymptotic quantization, scattering amplitudes, Carrollian holography, Twistor theory and twisted holography. This meeting will draw together experts on these various areas with a focus on asymptotic structure, symmetries, amplitudes and correlation functions, and the holographic theories that give rise to them. There will be an opportunity to celebrate the contributions of Ted Newman’s early work on flat space holography and instructional lectures on the more twistorial celestial holography frameworks that that work led to.
The meeting “From Good Cuts to Celestial Holography” was held at Oxford University, July 7-11 2025.
The workshop was held in honor of Ted Newman, an esteemed general relativist who pioneered early work on metric reconstruction from the asymptotic data of flat spacetime, a precursor of sorts to celestial holography. His contributions were reviewed by PI Tim Adamo, who explained how Newman’s “good cut” equation could be viewed as an early example of bulk reconstruction. Roger Penrose, a great pioneer of twistor theory (among many other contributions) was in attendance and was eager to learn about new developments in the field.
The meeting began with two lecture series by Simons Collaboration postdocs: Roland Bittleston on quantum field theories on twistor space, and Atul Sharma on twisted holography. They serve an important collaboration goal in bridging the language gap between several of the main tools used by Collaboration PIs, and the lectures enjoyed high engagement from the audience.
One theme of this workshop was the profound and rapid progress in using self-dual theories as toy models to understand aspects of celestial holography, and related, further advances in asymptotic symmetry algebras. PI David Skinner presented the in-progress twisted holographic construction for self-dual gravity, providing an update from his annual meeting talk, which stimulated important discussions about obstructions to locality in a dual field theory when gravity is deformed away from the self-dual limit. PI Andrew Strominger discussed on fascinating extensions of the classical S-algebra which admits no central charges compatible with Poincare invariance, but does admit SO(2,3)-compatible charges, which can be understood from both bottom-up and twistorial perspectives. Further, he proposed that the self-dual Yang-Mills vacuum on the Euclidean cylinder could be thought of as a thermofield double between two copies of AdS, and to understand properties of the central charge from the density matrix. PI Laurent Friedel and Adam Kmec spoke about symmetry algebras obtained from the symplectic structure of radiative modes at null infinity, which match beautifully with the classical chiral algebras from twistor space arguments studied by other Collaboration PIs. They also identify a Lie algebroid, rather than Lie algebra, structure inherent in such algebras on generic radiative backgrounds. The agreement and translation between these two different perspectives on symmetries arose directly from synergies within the Collaboration. PI Andrea Puhm described her work on subleading logarithmic soft theorems, which come from both classical late-time effects, as well as quantum effects, which also converge nicely with work by Sen et. al. (as in the annual meeting report).
Novel approaches to celestial holography and related topics were also represented at the workshop, and forging connections between these topics and Collaboration expertise is an exciting prospect for the future. PI Jordan Cotler explained various no-go arguments involving nontriviality of Carrollian QFTs with Lagrangian descriptions. He described technical puzzles that arise because of the ultralocality inherent in such theories, which manifest as delta-functions in propagators. He explored a simple regularization procedure from discretizing the celestial sphere, and how it limits to a free field theory. Yvgeny Skvortsov gave a review of higher spin theories and connections to self-dual 4d theories, including a 4d Poisson sigma model which enjoys a homotopical algebra structure, inviting further connections to the Collaboration’s work on twisted holography and higher algebras. Robert Wald gave a thorough overview on the infrared problem of defining a 4d S-matrix, in particular for non-abelian gauge theory and gravity, and in particular explained the connections between this classic problem with the memory effect.
Finally, the workshop hosted a variety of general relativity-focused presentations, with deep connections to twistor theory. Bernardo Araneda explained violations of the black hole uniqueness theorem in Euclidean signature, due to the Chen-Teo instanton, which has a complex structure (a possible hallmark for a twistorial background). Lydia Bieri discussed a variety of solutions to Einstein’s equations, focusing on gravitational radiation and the memory effect. Maciej Dunajski surveyed approaches to mass in general relativity from local and global perspectives, and explained in detail how casual properties depend sensitively on dimension.
Apr. 17, 2025 – Apr. 18, 2025
Thursday: 8:30 AM – 5 PM
Friday: 8:30 AM – 2 PM
Gerald D. Fischbach Auditorium
160 5th Avenue, New York, NY 10010
Speakers:
Kevin Costello*, Perimeter Institute
Nima Arkani Hamed*, Institute for Advanced Study
Raphael Bousso, Univerisity of California, Berkeley
Sabrina Pasterski*, Perimeter Institute
Ashoke Sen, International Center for Theoretical Sciences
Wei Song, Tsinghua University
David Skinner*, University of Cambridge
Edward Witten, Institute for Advanced Study
Meeting Goals:
A central goal of the Simons Collaboration on Celestial Holography is to find realizations of the holographic principle for quantum gravity in (nearly) flat spacetimes like the one we inhabit. The collaboration employs both top-down approaches guided by string and twistor theory and bottom-up approaches guided by soft theorems and asymptotic symmetries.
The 2025 annual meeting will bring together a wide range of theoretical physicists and mathematicians working on disparate topics relevant to this endeavor as well as observers pursuing detection of the associated memory effects. Speakers will both review foundational material and present recent developments across a range of approaches to quantum gravity and holography.
The 2025 annual meeting of the Simons Collaboration on Celestial Holography was held April 17–18th at the Simons Foundation, with 133 in-person participants representing a broad range of interests and perspectives.
A hallmark of the collaboration’s second year, and this annual meeting, has been an accelerating dialogue between Collaboration members and the theoretical physics community at large. In addition to Collaboration PI talks, invited speakers outside of the collaboration presented pioneering research congruent to Collaboration objectives.
The primary foci of the Collaboration are: (1) to find and understand universal quantum gravitational physics, including asymptotic symmetries, and their experimental signatures; (2) to find examples of celestial holography from the top down using string theory, and concomitant connections to mathematics; and (3) to advance our understanding of holography in general spacetimes, particularly asymptotically flat spacetimes. Significant progress was reported on all of these fronts at the meeting. Organizing meeting contributions by these three broad goals, a brief summary follows.
In brief, there was an influx of novel perspectives on the question of flat space holography, both from within and without the Collaboration. This stimulated further discussions and nascent collaborations among senior and junior scholars. Meal and coffee breaks were characterized by active discussions blending participants at all career stages, most of whom also attended the preceding two-day satellite meeting. Further, many results built on or were intimately connected to recent Collaboration achievements reported on at the previous annual meeting. For example, the work by Sen explored subleading logarithmic memory effects whose asymptotic symmetry interpretation was emphasized earlier by Andrea Puhm. The meeting reflected the rapid progress, stimulated by Collaboration activity, in the physics of holography for asymptotically flat spacetimes.
Apr. 15, 2025 – Apr. 16, 2025
9:30 AM – 5:30 PM
Andaz 5th Avenue
485 5th Avenue, New York, NY 10017
Glenn Barnich (Brussels)
Laurent Freidel (Perimeter)
Jelle Hartong (Edinburgh)
Daniel Kapec (Harvard)
Bob Knighton (Cambridge)
Beatrix Muehlmann (IAS)
Sruthi Narayanan (Perimeter)
Donal O’Connell (Edinburgh)
Julio Parra-Martinez (IHES)
Guilherme Pimentel (SNS Pisa)
Charlotte Sleight (Naples)
Stephan Stieberger (MPI Munich)
Raju Venugopalan (BNL)
Alexander Zhiboedov (CERN)
Feb. 10, 2025 – Feb. 21, 2025
Harvard University, Physics Department
17 Oxford St, Cambridge, MA 02138
This two-week-long Workshop on Celestial Holography was held at Harvard University from Feb 10-21, 2025. The aim of the workshop was primarily to bring experts together and foster interactions, with two to three talks held per day. There were 40 participants, including collaboration PI’s, postdocs and Ph.D. students. The informal discussions led to many new ideas for future work and helped start new collaborations between the participants.
Week 1: David Skinner kicked off the meeting by bringing up the big questions in celestial holography and discussing a specific top-down model that engineers self-dual Einstein gravity to answer some of them. Alfredo Guevara described the soft and collinear behavior of amplitudes involving particles with nonzero mass and spin, which led him to discover new extensions of the w-infinity algebra. Noah Miller looked at connections between maximal-helicity-violating graviton amplitudes and two-dimensional Wess-Zumino-Witten models, motivated by various graphical expansions and inverse soft recursion relations. Monica Pate discussed new developments in the debate about the spectrum of celestial CFT, elucidating the nature of operator product expansions involving local operators and their shadow transforms. Luca Ciambelli described advances in the geometry of null hypersurfaces and quantization of Carrollian theories, with special emphasis on null surfaces at finite distances. Albert Law reviewed his work on edge modes in de Sitter space and black holes, explaining their ubiquitous presence in the partition functions of gauge theories on manifolds with boundaries and corners. Mina Himwich continued with the theme of shadow transforms, showing that there are discrepancies between analyses based on celestial OPE blocks and those based on actual correlation functions. Eduardo Casali reviewed other attempts at finding a string theory embedding of self dual gravity, with the aim of finding a celestial holographic dual. Zixia Wei studied a one-dimensional toy model of entanglement between particles that is induced purely from their mutual gravitational interaction. Walker Melton constructed a basis of scattering states in Anti-de Sitter space and Klein space that transform in principal series representations of the conformal group.
Week 2: Lionel Mason described attempts to construct conserved charges for the algebra of asymptotic symmetries in self-dual Yang-Mills theory through its twistor action. Romain Ruzziconi reviewed Carrollian holography and explained how AdS Witten diagrams reduce to Carrollian amplitudes in the flat space limit of AdS/CFT. Akshay Yelleshpur Srikant gave more weight to the Carrollian proposal by means of studying the flat space limit of correlators of protected operators in ABJM theory. Andrew Strominger talked about the extension of Lorenztian CFT correlation functions from Minkowski space to the Einstein torus, which is the natural home of CFT in the embedding formalism. Tim Adamo discussed scattering in strong background fields and the associated twistor theory, obtaining new results for physically interesting backgrounds like lasers in QED. Sruthi Narayanan looked at distributional terms that can arise in the subsubleading soft graviton theorem, and attempted to derive them through on-shell recursion relations. Prahar Mitra explained the equivalence between two different characterizations of soft physics in QED: the soft-effective action and the edge mode action. Jordan Cotler reviewed lessons about quantum gravity (non-isometric encoding, Euclidean vs Lorentzian path integral, complex saddles, etc.), with explicit calculations performed in de Sitter JT gravity. Tom Taylor talked about the construction of scattering amplitudes in de Sitter space, based around the notion of what a de Sitter observer would see as their proper time elapses. Temple He explored the origins of t’Hooft’s commutation relations in a shockwave background, and derived them from an action principle which itself followed from a boundary term in Einstein gravity. Finally, Roland Bittleston concluded the workshop by discussing nonperturbative aspects of celestial holography, like computing amplitudes on instanton backgrounds in the bulk.
Jul. 22, 2024 – Jul. 26, 2024
Perimeter Institute for Theoretical Physics
PI/1-100 – Theatre
31 Caroline St N, Waterloo, ON N2L 2Y5, Canada
Description:
Perimeter Institute is happy to host the inaugural summer school for the Simons Collaboration on Celestial Holography July 22-26 in Waterloo, ON. The program will feature lectures on background material relevant for graduate students and postdocs interested in this emerging subfield, paired with vision talks on exciting future research directions.
Speakers:
Davide Gaiotto, Perimeter Institute
Lionel Mason*, University of Oxford
Prahar Mitra, Universiteit van Amsterdam
Sebastian Mizera, Institute for Advanced Study
Rob Myers, Perimeter Institute
Andrea Puhm*, University of Amsterdam
Ana-Maria Raclariu, King’s College London
Romain Ruzziconi, University of Oxford)
David Skinner*, University of Cambridge)
Andy Strominger*, Harvard University
*Collaboration PIs
The Celestial Holography Summer School 2024 was held at the Perimeter Institute for Theoretical Physics, July 22-26th. The focus of the school was to provide pedagogical introductions to the broad array of topics under active investigation under the purview of celestial and flat space holography. In addition to 15 lecturers and PIs, the school hosted 36 Masters/PhD students, 32 postdocs and PI residents, and 178 virtual participants.
In addition to the main lecture series, there were TA sessions held every day where students could work through lecturer-assigned exercises, supervised and assisted by expert postdoctoral researchers in the field of celestial holography, including Collaboration-affiliated postdocs. There was also a poster session, and a series of 7 lightning talks, to give junior members of the collaboration a chance to present their work. To bolster collaborative investigations, and promote the growth of Collaboration endeavors, the school concluded with a panel discussion featuring the Collaboration PIs, who shared future visions, exciting prospects, and pressing confusions and challenges, in an informal discussion with the school’s students.
Lecture series were split into two hour-long sessions each. Ana Maria Raclariu (King’s College) introduced celestial holography from a bulk perspective, culminating in the construction of asymptotic charges at null infinity, while Andrea Puhm (Amsterdam) explored a boundary CFT point of view, and elucidated how conformal representation theory provides an organizing principle on universal boundary degrees of freedom. Prahar Mitra (Amsterdam) introduced the covariant phase space formalism, and applied it to a first principles construction of the BMS symmetry in all dimensions. Sebastian Mizera (IAS) explored the physical imprints of Shapiro time delay in a scattering amplitudes calculation, emphasizing a quantum mechanical toy model, while Hofie Hannesdottir (IAS) gave an in-depth survey of various low-energy properties of the S-matrix, including proposals for how to correct and understand its definition when scattering states are subject to long-range potentials (i.e. are not asymptotically free). Romain Ruzziconi (Oxford) introduced Carrollian physics as an ultralocal limit of various conventional QFTs, and its application to a putative 3d Carrollian CFT dual at null infinity. David Skinner (Cambridge) provided a rapid survey of the geometry of twistor theory, culminating in discussions of holomorphic QFTs on twistor space and their connection with celestial physics; Davide Gaiotto (PI) explained how 2d holomorphic QFTs can be studied in the framework of twisted holography more generally, explained the large-N combinatoric observables they compute in the context of the AdS/CFT correspondence, and described various generalizations.
Finally, the school featured several research-level survey and vision talks, aimed towards providing a review of past work, and a jumping off point to important open research directions in celestial holography: Lionel Mason (Oxford) explained how celestial symmetry algebras may be deformed to incorporate nonzero cosmological constants, with a broad hope of realizing these symmetry algebras on the complete S-matrix of gravitational and gauge theories as an expansion around the self-dual sector, which enjoys these celestial symmetries. Rob Myers (PI) provided an overview of holographic entanglement entropy in AdS/CFT and its successes, and then described nascent but intriguing proposals which generalize this concept to flat spacetimes. Andrew Strominger (Harvard) provided a broad survey of the bottom-up approach to the celestial holography program and pointed to a host of open questions and puzzles, including the unusual distributional nature of low-point celestial CFT correlators and how they might be ameliorated by his leaf amplitude formulation, the question of how to constrain 4-pt scattering in the gravitational S-matrix given the underspecification of the Wilsonian approach, and connections to observing new memory effects at upcoming LIGO/LISA experiments.
Apr. 11, 2024 – Apr. 12, 2024
Thursday: 8:30 AM – 5 PM
Friday: 8:30 AM – 2 PM
Gerald D. Fischbach Auditorium
160 5th Avenue, New York, NY 10010
Speakers:
Geoffrey Compère, Université libre de Bruxelle
Lionel Mason*, University of Oxford
Shiraz Minwalla, Tata Institute of Fundamental Research
Natalie Paquette*, University of Washington
Andrea Puhm*, University of Amsterdam
Ana-Maria Raclariu, King’s College London & University of Amsterdam
Atul Sharma, Harvard University
Andy Strominger*, Harvard University
Meeting Goals:
A central goal of the Simons Collaboration on Celestial Holography is to find realizations of the holographic principle for quantum gravity in (nearly) flat spacetimes like the one we inhabit. The collaboration employs both top-down approaches guided by string and twistor theory and bottom-up approaches guided by soft theorems and asymptotic symmetries.
The 2024 annual meeting will bring together a wide range of theoretical physicists and mathematicians working on disparate topics relevant to this endeavor as well as observers pursuing detection of the associated memory effects. Speakers will review the foundations of the subject, present recent developments and explore future research focus areas.
Participants: Timothy Adamo* (University of Edinburgh), Nima Arkani-Hamed* (Institute for Advanced Study), Kevin Costello* (Perimeter Institute), Jordan Cotler* (Harvard University), Laurent Freidel* (Perimeter Institute), Lionel Mason* (University of Oxford), Natalie Paquette* (University of Washington), Sabrina Pasterski* (Perimeter Institute), Andrea Puhm* (University of Amsterdam), David Skinner* (DAMTP, Cambridge), Andy Strominger* (Harvard University), Tomasz Taylor* (Northeastern University), Clifford Cheung (Caltech), Holmfridur Hannesdottir (IAS Princeton), Luis Alday (University of Oxford), Arjun Bagchi (Indian Institute of Technology Kanpur), Adam Ball (Perimeter Institute), Glenn Barnich (Université Libre de Bruxelles), Christopher Beem (University of Oxford), Arindam Bhattacharjee (University of Warsaw), Roland Bittleston (Perimeter Institute), Giuseppe Bogna (University of Oxford), Raphael Bousso (UC Berkeley), Graham Brown (Queen Mary University of London), Wei Bu (University of Edinburgh), Katarzyna Budzik (Perimeter Institute), Miguel Campiglia Curcho (Universidad de la Republica), Lucile Cangemi (Uppsala University), Federico Capone (FSU Jena), Eduardo Casali (Harvard University), Chi-Ming Chang (Tsinghua University), Sangmin Choi (University of Amsterdam), Luca Ciambelli (Perimeter Institute), Scott Collier (MIT), Frank Coronado Idrogo (ETH Zurich), Erin Crawley (Harvard University), Nicolas Cresto (Perimeter Institute), Daine Danielson (University of Chicago), Shounak De (Brown University), Jan de Boer (University of Amsterdam), Samuel DeHority (Columbia University), Frederik Denef (Columbia University), Tudor Dan Dimofte (University of Edinburgh), Netta Engelhardt (MIT), Wei Fan (Jiangsu University of Science and Technology), Ricardo Jorge Ferreira Monetero (QMUL – Remote Participant), Eanna Flanagan (Cornell University), Ping Gao (Rutgers University), Marc Geiller (ENS de Lyon), Sudip Ghosh (Technion, University of Haifa – Remote Participant), Gaston Giribet (New York University), Hernán González Leiva (Universidad San Sebastian), Joshua Gowdy (Queen Mary University of London), Samuel Gralla (University of Arizona), Akexander Grant (University if Southampton – Remote Participant), Alfredo Guevara Gonzalez (Harvard University), Daniel Harlow (MIT), Jelle Hartong (University of Edinburgh), Emil Have (Niels Bohr Institute), Song He (Institute of Theoretical Physics, Chinese Academy of Sciences – Remote Participant), Temple He (Caltech), Carlo Heissenberg (Queen Mary University of London), Simon Heuveline (University of Cambridge), Matthew Heydeman (Harvard University), Elizabeth Himwich (Princeton University), Yangrui Hu (Perimeter Institute), Diksha Jain (Tata Institute of Fundamental Research, Mumbai), Eivind Hilmen Jorstad (Perimeter Institute), Daniel Kapec (Harvard University), Sonja Klisch (University of Edinburgh), Adam Kmec (Mathematical Institute, University of Oxford), Robert Knighton (University of Cambridge), Uri Kol (Harvard University), Per Kraus (UCLA), Hare Krishna (Stony Brook University), Harshal Kulkarni (Tata Institute of Fundemental Research, Mumbai – Remote Participant), Guilherme Leite Pimentel (Scuola Normale Superiore), Madalena Lemos (Durahm University – Remote Participant), Pujian Mao (Tianjin University – Remote Participant), Walker Melton (Harvard University), Noah Miller (Harvard University), Olivera Miskovic (Pontificia Universidad Catolica de Valparaiso), Prahar Mitra (University of Amsterdam), Sebastian Mizera (IAS Princeton), Igor Mol Bessa (Unicamp), Ruben Monten (CERN), Ian Moult (Yale University), Beatrix Muehlmann (McGill University), Richard Myers (UCLA), Parameswaran Nair (City College of New York), Sruthi Narayanan (Perimeter Institute), Kévin Nguyen (Université Libre de Bruxelles), David Nichols (University of Virginia), Alberto Nicolis (Columbia University), Filip Niewinski (Harvard University), Maria Nocchi (University of Oxford), Niels Obers (Niels Bohr Institute & Nordita), Gerben Oling (University of Edinburgh), Yorgo Pano (CPHT – Ecole Polytechnique), Partha Paul (Indian Institute of Science, Bangalore), Alfredo Perez (Center for Scientific Studies), Leonardo Pipolo de Gioia (ICTP-SAIFR/IFT-UNESP), Massimo Porrati (New York University), Siddharth Prabhu (TIFR – Remote Participant), Daniele Pranzetti (Udine University), Himanshu Raj (Stony Brook University), Leonardo Rastelli (YITP, Stony Brook), Lecheng Ren (Brown University), Maria Rodriquez (Utah State University / IFT UAM-CSIC), Victor Rodriguez (Princeton University), Radu Roiban (Pennsylvania State University), Francisco Rojas Fernandez (Universidad Adolfo Ibáñez), Romain Ruzziconi (University of Oxford), Amartya Saha (Indian Institute of Technology Kanpur – Remote Participant), Biswajit Sahoo (King’s College London), Gautam Satishchandran (Princeton University), John Schwarz (Caltech – Remote Participant), Sean Seet (University of Cambridge), Ali Seraj (Université libre de Bruxelles), Ahmed Sheta (Harvard University), Pushkal Shrivastava (Harvard University), Guillermo Silva (Universidad Nacional de La Plata), Konstantinos Skenderis (University of Southampton), Evgeny Skvortsov (Mons), Wei Song (Tsinghua University), Manu Srivastava (MIT), Sotaro Sugishita (Kyoto University), Haoyu Sun (UT Austin), Iustin Surubaru (The University of Edinburgh), Marika Taylor (University of Birmingham), Chiara Toldo (Harvard University), Andrew Tolley (Imperial College London), Marija Tomašević (University of Amsterdam), Piotr Tourkine (LAPTh, CNRS), Tung Tran (Vienna University), Emilio Trevisani (LPTHE), Adam Tropper (Harvard University), Oscar Varela (Utah State University and IFT-Madrid), Raju Venugopalan (Brookhaven National Laboratory and Stony Brook University), Evita Verheijden (Harvard University), Herman Verlinde (Princeton University), Dindian Wang (Harvard University), Tianli Wang (Harvard University), Zixia Wei (Harvard University), Sam Wikeley (Uppsala University), Michelle Xu (Stanford University – Remote Participant), Herfray Yannick (Université de Tours – Remote Participant), Akshay Yelleshpur Srikant (University of Oxford), Keyou Zeng (Perimeter Institute), Bin Zhu (University of Edinburgh), Kathryn Zurek (Caltech), Céline Zwikel (Perimeter Institute).
*Collaboration PIs
The first annual meeting of the Simons Collaboration in Celestial Holography (CH) was held on April 11-12th, 2024, with 142 in-person participants and an additional 14 remote participants. In addition to the speakers, the meeting was attended by CH PIs and postdoctoral fellows, distinguished faculty members working on related topics, and many other graduate students and postdocs. The meeting was immediately preceded by a two-day satellite meeting (April 9-10th), held at the ANDAZ hotel, featuring 14 stimulating talks with topics ranging from the mathematics of chiral algebras and top-down stringy models of celestial holography, to a detailed overview of short and long-term prospects for the experimental observation of gravitational memory effects. At the annual meeting, there were also 13 posters presented by graduate students, which became the focal point for many active discussions during the breaks between plenary talks, as well as after the final talk. The annual meeting kicked off with collaboration director Andrew Strominger (Harvard) giving an overview of approaches, successes, and both short and long-term
goals for the collaboration. He reviewed the deep connections between Weinberg’s soft theorems, memory effects, and asymptotic symmetries, pioneered by his group, which initially galvanized the subject. Collaboration goals ranged from the complete determination of the symmetries of asymptotically flat spacetimes to the construction of toy models from string theory, and prospects for experimental detection of memory effects. He paid particular emphasis to the bottom-up approach to CH, by which one can deduce properties of the putative celestial dual from known scattering processes. This approach is universal, independent of any special stringy realization or concomitant assumptions of a celestial holographic duality, and therefore suitable for revealing broad lessons about quantum gravity including in our own universe. He also highlighted crowdsourced questions, for inspiring future work on CH, from collaboration members, affiliates, and colleagues which are now available on the collaboration website.
Ana-Maria Raclariu (U. Amsterdam) explained how one can take flat-space limits of observables in the much-studied AdS/CFT correspondence to reproduce and explain various exotic features of celestial amplitudes describing the scattering of massless particles. She included a beautiful alternative derivation of the infinite tower of symmetries recently discovered in CH from this approach, exhibiting the potential of realizing a celestial CFT within a higher-dimensional CFT which itself participates in an AdS/CFT duality.
Shiraz Minwalla (TIFR) explained his recent tour-de-force work describing a formulation of (a generalization of) the S-matrix realized as a functional of boundary values. This approach generalizes the study of local singularities called “bulk point singularities” from AdS to flat spacetimes, and generalizing the analysis to include multi-bulk point singularities. His construction has potentially fascinating ramifications for understanding emergent bulk locality in asymptotically flat spacetimes.
Natalie Paquette (U. Washington), a collaboration PI, reviewed the twistorial approach to 4d amplitudes and asymptotic symmetries pioneered by herself and fellow PI Costello, which has been used recently to construct a top-down example of a CH duality from string theory. She then presented new results, including the first determination of a fully quantum-corrected asymptotic symmetry algebra, including deformations at all loops. In 4d, this provides an all-orders result for collinear splitting functions in a version of QCD coupled to special choices of matter.
Atul Sharma (Harvard), a collaboration postdoc, described a celestial CFT dual for MHV amplitudes in gauge theory by coupling a certain large-N chiral algebra to Liouville theory. He emphasized a novel structure called leaf amplitudes as a natural celestial quantity, and explained how they can be recombined to understand unusual distributional features of standard celestial amplitudes.
Geoffrey Compere (U.L.Bruxelle) resolved a fundamental puzzle in the definition of asymptotically flat spacetimes, by explaining how the five asymptotic boundaries of flat spacetime could be consistently joined in a manner compatible with a single action of the BMS group, which encodes the asymptotic symmetries general relativity. His construction accommodated logarithmic corrections to soft theorems and was used to derive celestial conserved charges. He also explained generalizations and challenges for de Sitter spacetimes.
Lionel Mason (Oxford), a collaboration PI, provided a pedagogical overview of key aspects of the twistorial formulation of massless physics on flat spacetimes, and explained how twistorial methods generalize to spacetimes with nonvanishing cosmological constant. He used this approach to derive a deformation of the walgebra obtained by Strominger et. al. for AdS spacetimes. In addition, he explained work in progress connecting infinite towers of celestial charges obtained by Friedel (collaboration PI) and others, to integrable hierarchies which are manifest on twistor space.
Andrea Puhm (U. Amsterdam), a collaboration PI, explored a logarithmic class of quantum corrections to soft theorems in scalar QED and general relativity (GR). She demonstrated that these subleading effects were universal, much like the vaunted leading soft theorems in QED and GR. Moreover, she provided a first-principles derivation that these corrections correspond to genuine asymptotic symmetries associated to conserved charges.
Apr. 9, 2024 – Apr. 10, 2024
9:30 AM – 5:30 PM
Andaz 5th Avenue
485 5th Avenue, New York, NY 10017
Fernando Alday, University of Oxford
Adam Ball, Perimeter Institute
Kasia Budzik, Perimeter Institute
Jan de Boer, University of Amsterdam
Frank Coronado, ETH-Zurich
Kevin Costello, Perimeter Institute
Per Kraus, University of California, Los Angeles
Prahar Mitra, University of Amsterdam
Ian Moult, Yale University
David Nichols, University of Virginia
Massimo Porrati, New York University
Romain Ruzziconi, University of Oxford
Bin Zhu, University of Edinburgh
Kathryn Zurek, Caltech
Participants: Timothy Adamo* (University of Edinburgh), Kevin Costello* (Perimeter Institute), Jordan Cotler* (Harvard University), Laurent Freidel* (Perimeter Institute), Lionel Mason* (University of Oxford), Natalie Paquette* (University of Washington), Sabrina Pasterski* (Perimeter Institute), Andrea Puhm* (University of Amsterdam), David Skinner* (DAMTP, Cambridge), Andy Strominger* (Harvard University), Tomasz Taylor* (Northeastern University), Luis Alday (University of Oxford), Arjun Bagchi (Indian Institute of Technology Kanpur), Adam Ball (Perimeter Institute), Glenn Barnich (Université Libre de Bruxelles), Christopher Beem (University of Oxford), Roland Bittleston (Perimeter Institute), Giuseppe Bogna (University of Oxford), Raphael Bousso (UC Berkeley), Graham Brown (Queen Mary University of London), Wei Bu (University of Edinburgh), Kasia Budzik (Perimeter Institute), Miguel Campiglia Curcho (Universidad de la Republica), Lucile Cangemi (Uppsala University), Federico Capone (FSU Jena), Eduardo Casali (Harvard University), Sangmin Choi (University of Amsterdam), Luca Ciambelli (Perimeter Institute), Frank Coronado Idrogo (ETH Zurich), Erin Crawley (Harvard University), Daine Danielson (University of Chicago), Shounak De (Brown University), Jan de Boer (University of Amsterdam), Tudor Dan Dimofte (University of Edinburgh), Wei Fan (Jiangsu University of Science and Technology), Marc Geiller (ENS de Lyon), Sudip Ghosh (Technion, University of Haifa – Remote Participant), Gaston Giribet (New York University), Hernán González Leiva (Universidad San Sebastian), Joshua Gowdy (Queen Mary University of London), Alfredo Guevara Gonzalez (Harvard University), Jelle Hartong (University of Edinburgh), Emil Have (Niels Bohr Institute), Temple He (Caltech), Simon Heuveline (University of Cambridge), Matthew Heydeman (Harvard University), Elizabeth Himwich (Princeton University), Yangrui Hu (Perimeter Institute), Diksha Jain (Tata Institute of Fundamental Research, Mumbai), Eivind Hilmen Jorstad (Perimeter Institute), Daniel Kapec (Harvard University), Sonja Klisch (University of Edinburgh), Adam Kmec (Mathematical Institute, University of Oxford), Robert Knighton (University of Cambridge), Uri Kol (Harvard University), Per Kraus (UCLA), Harshal Kulkarni (Tata Institute of Fundemental Research, Mumbai – Remote Participant), Guilherme Leite Pimentel (Scuola Normale Superiore), Walker Melton (Harvard University), Noah Miller (Harvard University), Olivera Miskovic (Pontificia Universidad Catolica de Valparaiso), Prahar Mitra (University of Amsterdam), Igor Mol Bessa (Unicamp), Ruben Monten (CERN), Ian Moult (Yale University), Richard Myers (UCLA), Sruthi Narayanan (Perimeter Institute), Kévin Nguyen (Université Libre de Bruxelles), David Nichols (University of Virginia), Filip Niewinski (Harvard University), Maria Nocchi (University of Oxford), Niels Obers (Niels Bohr Institute & Nordita), Gerben Oling (University of Edinburgh), Yorgo Pano (CPHT – Ecole Polytechnique), Alfredo Perez (Center for Scientific Studies), Leonardo Pipolo de Gioia (ICTP-SAIFR/IFT-UNESP), Massimo Porrati (New York University), Daniele Pranzetti (Udine University), Himanshu Raj (Stony Brook University), Leonardo Rastelli (YITP, Stony Brook), Lecheng Ren (Brown University), Maria Rodriquez (Utah State University / IFT UAM-CSIC), Radu Roiban (Pennsylvania State University), Francisco Rojas Fernandez (Universidad Adolfo Ibáñez), Romain Ruzziconi (University of Oxford), Biswajit Sahoo (King’s College London), Gautam Satishchandran (Princeton University), Sean Seet (University of Cambridge), Ali Seraj (Université libre de Bruxelles), Ahmed Sheta (Harvard University), Guillermo Silva (Universidad Nacional de La Plata), Wei Song (Tsinghua University), Manu Srivastava (MIT), Sotaro Sugishita (Kyoto University), Haoyu Sun (UT Austin), Iustin Surubaru (The University of Edinburgh), Marika Taylor (University of Birmingham), Marija Tomašević (University of Amsterdam), Piotr Tourkine (LAPTh, CNRS), Tung Tran (Vienna University), Emilio Trevisani (LPTHE), Adam Tropper (Harvard University), Oscar Varela (Utah State University and IFT-Madrid), Evita Verheijden (Harvard University), Herman Verlinde (Princeton University), Dindian Wang (Harvard University), Tianli Wang (Harvard University), Zixia Wei (Harvard University), Sam Wikeley (Uppsala University), Akshay Yelleshpur Srikant (University of Oxford), Keyou Zeng (Perimeter Institute), Bin Zhu (University of Edinburgh), Céline Zwikel (Perimeter Institute).
*Collaboration PIs
A satellite meeting of the Simons Collaboration on Celestial Holography (CH) was held on April 9-10th, 2024 at the ANDAZ hotel in NYC, with 135 in-person participants. In addition to the speakers, the meeting was attended by CH PIs and postdoctoral fellows, distinguished faculty members working on related topics, and many other graduate students and postdocs. Many of the talks at the satellite meeting dovetailed with the annual meeting talks, so that all participants were exposed to both review and cutting-edge perspectives on the key topics in CH.
The two day meeting included 14 talks, with one hour long ‘plenary’ talk each day, and 6 additional half-hour long talks per day. The plenary session on day 1 was given by Jan de Boer (Amsterdam) who reviewed fundamental results about the statistical mechanics interpretation of semiclassical gravity and the Euclidean path integral, ensemble averaging in holography, and the connections to random matrix theory. The second plenary lecture was by David Nichols (U. Virginia) who provided a status update of gravitational wave detectors, a review of the gravitational memory effects (including subleading/spin memory effects discovered from bottom-up CH), and prospects for experimental detection in the current and future generation of detectors.
The other speakers gave seminar-style talks providing updates on a variety of the interconnected fields of which the CH collaboration is composed. Topics covered included twisted holography (Costello, Budzik), determinant operators in holography (Coronado, Budzik), amplitudes in strong field (Bu, Costello) or AdS (Alday) backgrounds, twistorial methods for MHV scattering (Klisch), light ray observables at the LHC (Moult), Carrollian perspectives on scattering (Kraus) and as related to flat limits of AdS (Ruzziconi), bottom-up approaches to CH including new perspectives on the contour of Mellin transforms (Mitra) and supertranslation symmetries (Porrati) and clarifications on the appearance of edge modes in path integral computations of the entanglement entropy (Ball).
Oct. 26, 2023 – Oct. 29, 2023
Jefferson Laboratory, Harvard University
17 Oxford St, Cambridge, MA 02138
Confirmed Speakers: Tim Adamo* (University of Edinburgh), Nima Arkani-Hamed* (IAS), Shamik Banerjee (NISER, Bhubaneswar, India), Roland Bittleston (Perimeter Institute), Wei Bu (University of Edinburgh), Miguel Campiglia (Universidad de la República), Eduardo Casali (Harvard University), Luca Ciambelli (Perimeter Institute), Sangmin Choi (Ecole Polytechnique), Kevin Costello* (Perimeter Institute), Jordan Cotler* (Harvard), Lance Dixon (SLAC/Stanford), Laura Donnay (SISSA), Roberto Emparan (ICREA and University of Barcelona), Laurent Freidel* (Perimeter Institute), Daniel Grumiller (TU Wien), Temple He (Caltech), Elizabeth Himwich (Princeton University), Yangrui Hu (Perimeter Institute), Dan Kapec (Harvard University), Alok Laddha (Chennai Mathematical Institute), Lorenzo Magnea (University of Torino), Juan Maldacena (IAS), Lionel Mason* (University of Oxford), Prahar Mitra (University of Cambridge), Rob Myers (Perimeter Institute), Natalie Paquette* (University of Washington), Sabrina Pasterski* (Perimeter Institute), Malcolm John Perry (University of Cambridge), Andrea Puhm* (University of Amsterdam), Francisco Rojas (Universidad Adolfo Ibáñez), John H. Schwarz (Caltech), Ali Seraj (Queen Mary University of London), Atul Sharma (Harvard University), Eva Silverstein (Stanford), David Skinner* (DAMTP, Cambridge), Marcus Spradlin (Brown University), Andrew Strominger* (Harvard), Tadashi Takayanagi (YITP), Tomasz Taylor* (Northeastern University), Anastasia Volovich (Brown University), Robert Wald (University of Chicago), Diandian Wang (Harvard University), Alexander Zhiboedov (CERN)
*Collaboration PIs
The kickoff meeting of the Simons Collaboration in Celestial Holography was attended by the collaboration PIs, their postdocs and students, and many other faculty and junior researchers working in the field. Attendance was capped at 207 attendees, due to the venue’s recorded maximum capacity.
Collaboration PIs and postdocs gave short 10+5 minute talks and other speakers gave 20+5 minute talks. There were 41 talks in all (not counting a small number of cancellations due to illness/visa issues); we can give only a lightning summary of these many thrilling contributions below. Talk categorizations by topic are approximate.
Bottom-Up Holography/Celestial Symmetries: Andrew Strominger leveraged the fact that Minkowski space has regions which can be foliated by lower dimensional de Sitter spacetimes; this fact motivates the use of special states called alpha-vacua, which can ameliorate puzzling aspects of the CCFT correspondence. Alfredo Guevara proposed a toy model for a Hilbert space in celestial holography that is protected by quantum error correction. Andrea Puhm used CFT technology to clarify the difference between CCFT symmetries and asymptotic symmetries in spacetime. Akshay Yelleshpur discussed conditions for associativity of celestial OPEs, and simplifications that arise in the presence of supersymmetry. Sangmin Choi explained how divergent 1-loop corrections to the subleading soft theorem correspond to certain large gauge transformations with long-range interactions. Atul Sharma elucidated functional forms of CFT correlators that live on the boundary of the Klein spacetime of (2, 2) signature, “the celestial torus”. Daniel Grumiller presented general arguments that a CCFT will satisfy the mathematical axioms of a log-CFT. Diandian Wang used on-shell recursion relations to fix the expansion of a classical celestial OPE. Laura Donnay explained that the logarithmic soft theorems in gravity arise from Ward identities associated to supperotations. Shamik Banerjee derived the most general OPE governing +-helicity gravitons compatible with the infinite-dimensional classical symmetry algebra. John Schwarz discussed suggestive properties of celestial OPEs for a variety of theories. Prahar Mitra presented higher-dimensional generalizations of the BMS group. Yangrui Hui proposed that integrated multi-particle states should be included in the celestial OPEs and are related to mulit-collinear limits. Laurent Friedel employed the classical Poisson bracket approach to characterizing asymptotic symmetries in GR. Sabrina Pasterski emphasized important open questions in CCFT. Robert Myers initiated the study of entanglement entropy in CCFT and its dual. Temple He studied the phase space of higher-dimensional Yang-Mills theory. Miguel Campiglia extended the usual gravitational phase space at null infinity to achieve Diff(S^2) covariance. Dan Kapec connected non-commuting soft limits with the existence of a CCFT conformal manifold.
Top-Down Holography/Twistors: Francisco Rojas explained how string theory amplitudes in the celestial basis can recover field theory amplitudes in a certain limit. Kevin Costello discussed a new top-down celestial holography construction for self-dual Yang-Mills with matter, using intersecting stacks of branes in the topological string. Roland Bittleston described an extended celestial chiral algebra based on self-dual gravity, motivated from twistor space, that characterizes special deformations of SDGR. Wei Bu constructed a 2d CFT from large gauge transformations of SDYM using scaling reductions on twistor space. Lionel Mason recalled twistorial approaches to reconstruct flat spacetime from asymptotic data. Tim Adamo explored scattering in the presence of strong background fields with twistorial methods. Eduardo Casali described how 4d Goldstone modes appear as generalized Wilson lines in twistor space and derived their OPEs. David Skinner reported on progress constructing twisted holographic celestial duals for gravitational theories on Ricci-flat Kahler metrics.
Amplitudes & Bootstrap: Lance Dixon reported on an astonishing and still-mysterious duality relating different high-loop planar amplitudes in N=4 super Yang-Mills. Lorenzo Magnea mapped the factorization properties of IR divergences in gauge theory amplitudes to the celestial sphere, and explained how that suggests a representation of the soft scattering as a free gauge-valued bosonic CCFT. Leonardo Rastelli presented new bounds on pion scattering in large-N QCD using bootstrap techniques. Sam Gralla derived formulas for BMS charges at all infinities and determined BMS-covariant notions of impact parameter and spin for classical gravitational scattering. Mina Himwich delineated nonlocal properties of celestial scattering amplitudes including massive particles.
Memory Effects & Soft Modes: Robert Wald clarified numerous formal consequences of asymptotic symmetries and memory for QFT scattering. Luca Ciambelli presented novel solutions and conservation laws related to the null Raychaudhuri equation, and interpreted it as a stress-tensor inequality. Ali Seraj introduced a new gyroscopic gravitational memory effect and discussed its prospects for detection. Eanna Flanagan examined lore about the behavior of classical soft modes and the consequences for black hole soft hair and information content.
Related Advances (AdS, dS, & more): Eva Silverstein reported on a trove of recent progress constructing holographic duals for patches of 3d de Sitter (dS) spacetimes, including computations of the dS entropy, by applying a combination of controlled deformations from familiar AdS/CFT examples. Jordan Cotler revisited other approaches to dS holography such as dS/CFT, as well as new nonperturbative tools for studying gravity in dS. Juan Maldacena discussed aspects of a universal double-cone wormhole solution in AdS/CFT which explains the ramp in the spectral form factor that arises in general chaotic systems. Tadashi Takayanagi proposed the concept of pseudo-entropy as the appropriate holographic version of entanglement entropy for celestial and dS holography. Roberto Emparan resolved old puzzles about how spinning string states interpolate to higher-dimensional black objects as they become strongly interacting.