2026 Simons Collaboration on Celestial Holography Annual Meeting

Fernando Alday
University of Oxford

On the Soft Behaviour of N=4 SYM

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

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

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

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

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

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

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

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.

Participation in the meeting falls into the following four categories. An individual’s participation category is communicated via their letter of invitation.

The Simons Foundation will never ask for credit card information or require payment for registration to our events.

Group A – Speakers & Organizers

Individuals in Group A receive travel and hotel coordination within the following parameters:

Travel
Economy Class: For flights that are three hours or less to your destination, the maximum allowable class of service is Economy class.
Premium Economy Class: For flights where the total air travel time (excluding connection time) is more than three hours and less than seven hours per segment to your destination, the maximum allowable class of service is premium economy.
Business Class: When traveling internationally (or to Hawaii/Alaska) travelers are permitted to travel in Business Class on those segments that are seven hours or more. If the routing is over budget, a premium economy or mixed-class ticket will be booked.

Hotel
Up to three nights at the conference hotel, arriving on Wednesday, April 15 and departing on Saturday, April 18.

Group B – Funded Participants

Individuals in Group B receive travel and hotel coordination within the following parameters:

Travel
Economy class travel will be booked regardless of flight length.

Hotel
Up to three nights at the conference hotel, arriving on Wednesday, April 15 and departing on Saturday, April 18.

Group C – Unfunded Participants

Individuals in Group C will not receive financial support but are encouraged to enjoy all conference-hosted meals.

Group D – Remote Participants

Individuals in Group D will participate in the meeting remotely.

Air and Rail

For funded individuals, the foundation will arrange and pay for round-trip travel from their home city to the conference city. All travel and hotel arrangements must be booked through the Simons Foundation’s preferred travel agency.

Travel Deviations

The following travel specifications are considered deviations and will only be accommodated if the cost is less than or equal to the amount the Simons Foundation would pay for a standard round-trip ticket from your home city to the conference city:

• Preferred airline
• Preferred travel class
• Specific flights/flight times
• Travel dates outside those associated with the conference
• Arriving or departing from an airport other than your home city or conference city airports, i.e. multi-segment or triangle trips.

All deviations must be reviewed and approved by the Simons Foundation and, if the cost is more than what would normally be paid, a reimbursement quote must be obtained through the foundation’s travel agency before proceeding to booking and paying for travel out of pocket. All reimbursements for travel booked directly will be paid after the conclusion of the meeting.

Changes After Ticketing

All costs related to changes made to ticketed travel are to be paid for by the participant and are not reimbursable. Please contact the foundation’s travel agency for further assistance.

Personal & Rental Cars

Personal car and rental trips over 250 miles each way require prior approval from the Simons Foundation via email.

Rental cars must be pre-approved by the Simons Foundation.

The Royalton Park Avenue offers valet parking. Please note there are no in-and-out privileges when using the hotel’s garage, therefore it is encouraged that participants walk or take public transportation to the Simons Foundation.

Hotel

Funded individuals who require hotel accommodations are hosted by the foundation for a maximum of three nights, arriving on Wednesday, April 15 and departing on Saturday, April 18.

Any additional nights are at the attendee’s own expense. To arrange accommodations, please register at the link included in your invitation.

Royalton Park Avenue
420 Park Ave S.
New York, NY 10016
https://www.royaltonparkavenue.com/

For driving directions to the Royalton Park Avenue, please click here.

Overview

In-person participants will be reimbursed for meals and local expenses including ground transportation. Expenses should be submitted through the foundation’s online expense reimbursement platform after the meeting’s conclusion.

Expenses accrued because of meetings not directly related to the Simons Foundation-hosted meeting (a satellite meeting or meeting held at another institution, for example) will not be reimbursed by the Simons Foundation and should be paid by other sources.

Below are key reimbursement takeaways; a full policy will be provided with the final logistics email circulated approximately 2 weeks prior to the meeting’s start.

Meals

The daily meal limit is $125; itemized receipts are required for expenses over $24 USD. The foundation DOES NOT provide a meal per diem and only reimburses actual meal expenses up the following amounts.

• Breakfast $20
• Lunch $30
• Dinner $75

Allowable Meal Expenses

• Meals taken on travel days (when you traveled by air or train).
• Meals not provided on a meeting day, dinner on Friday for example.
• Group dinners consisting of fellow meeting participants paid by a single person will be reimbursed up to $75 per person and the amount will count towards the $125 daily meal limit.

Unallowable Meal Expenses

• Meals taken outside those provided by the foundation (breakfast, lunch, breaks and/or dinner).
• Meals taken on days not associated with Simons Foundation-coordinated events.
• Minibar expenses.
• Meal expenses for a non-foundation guest.

• Ubers, Lyfts, taxis, etc., taken to and from restaurants in Manhattan.

  • Accommodations will be made for those with mobility restrictions.

Ground Transportation

Expenses for ground transportation will be reimbursed for travel days (i.e. traveling to/from the airport or train station) as well as subway and bus fares while in Manhattan are reimbursable.

Transportation to/from satellite meetings are not reimbursable.

Attendance

In-person participants and speakers are expected to attend all meeting days. Participants receiving hotel and travel support wishing to arrive on meeting days which conclude at 2:00 PM will be asked to attend remotely.

Entry & Building Access

Upon arrival, guests will be required to show their photo ID to enter the Simons Foundation and Flatiron Institute buildings. After checking-in at the meeting reception desk, guests will be able to show their meeting name badge to re-enter the building. If you forget your name badge, you will need to provide your photo ID.

The Simons Foundation and Flatiron Institute buildings are not considered “open campuses” and meeting participants will only have access to the spaces in which the meeting will take place. All other areas are off limits without prior approval.

If you require a private space to conduct a phone call or remote meeting, please contact your meeting manager at least 48-hours ahead of time so that they may book a space for you within the foundation’s room reservation system.

Guests & Children

Meeting participants are required to give 24-hour advance notice of any guests meeting them at the Simons Foundation either before or after the meeting. Outside guests are discouraged from joining meeting activities, including meals.

With the exception of Simons Foundation and Flatiron Institute staff, ad hoc meeting participants who did not receive a meeting invitation directly from the Simons Foundation are not permitted.

Children under the age of 18 are not permitted to attend meetings at the Simons Foundation. Furthermore, the Simons Foundation does not provide childcare facilities or support of any kind. Special accommodations will be made for nursing parents.

Meeting & Policy Questions

Meghan Fazzi
Senior Manager, Events & Administration
Division of Mathematics & Physical Sciences
[email protected]

Travel & Hotel Support

FCM Travel Meetings & Events
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