2024 Simons Collaboration on Celestial Holography Annual Meeting

Geoffrey Compère
Université Libre de Bruxelle

Progress on the Definition of Asymptotically Flat and de Sitter Spacetimes

The definition of scattering in asymptotically flat spacetimes requires to consistently match its five asymptotic boundaries: past/future timelike and null infinities and spatial infinity. I will present a framework consistent with logarithmic corrections to soft theorems where a single BMS group acts on all boundaries and where individual ingoing/outgoing bodies are ascribed initial/final BMS charges. Using the post-Minkowskian expansion, I will demonstrate that non-radiative regions are entirely characterized by a set of conserved celestial charges that consist of the Geroch-Hansen multipole moments, the generalized BMS charges and additional non-stationary multipole moments. In the context of asymptotically de Sitter spacetimes, I will finally demonstrate that the presence of a quadrupole moment of any localized source in de Sitter leads to a fluctuating boundary metric that breaks the conjectured conformal asymptotic symmetry group. Dynamical Einstein gravity in de Sitter cannot therefore be modelled by a 3d CFT.
 

Lionel Mason
University of Oxford

Twistor Approaches to Celestial Symmetries and their AdS Deformations

This talk will review the twistor origins of celestial symmetry algebras and their extension to AdS. It will go on to discuss connections with the integral systems literature and top-down approaches to celestial holography via twistor actions and chiral sigma models and (ambi-)twistor strings.
 

Shiraz Minwalla
Tata Institute of Fundamental Research

The S-Matrix and Boundary Correlators in Flat Space

We consider the path integral of a quantum field theory in Minkowski spacetime with fixed boundary values (for the elementary fields) on asymptotic boundaries. We define and study the corresponding boundary correlation functions obtained by taking derivatives of this path integral with respect to the boundary values. The S-matrix of the QFT can be extracted directly from these boundary correlation functions after smearing. We interpret this relation in terms of coherent state quantization and derive the constraints on the path-integral as a function of boundary values that follow from the unitarity of the S-matrix. We then study the locality structure of boundary correlation functions. In the massive case, we find that the boundary correlation functions for generic locations of boundary points are dominated by a saddle point which has the interpretation of particles scattering in a small elevator in the bulk, where the location of the elevator is determined dynamically, and the S-matrix can be recovered after stripping off some dynamically determined but non-local “renormalization” factors. In the massless case, we find that while the boundary correlation functions are generically analytic as a function on the whole manifold of locations of boundary points, they have special singularities on a sub-manifold, points on which correspond to light-like scattering in the bulk. We completely characterize this singular scattering sub-manifold and find that the corresponding residues of the boundary correlations at these singularities are precisely given by S-matrices. This analysis parallels the analysis of bulk-point singularities in AdS/CFT and generalizes it to the case of multi-bulk point singularities.
 

Natalie Paquette
University of Washington

Associativity is Enough

I will report on work to appear shortly with my student, Victor Fernandez. The celestial chiral algebras of “twistorial” theories, 4d theories with local holomorphic lifts to twistor space, are associative even at the quantum level. In this work, we use elementary considerations, such as symmetries and associativity, to find closed-form expressions for all coefficients (i.e., at arbitrary loop order) of the OPEs for the celestial chiral algebras associated to twistorial theories, in particular self-dual Yang-Mills theory coupled to special choices of matter; similar considerations apply also for self-dual general relativity coupled to a special matter sector. This work constitutes a preliminary step in a program proposed by Costello and myself called the chiral algebra bootstrap, in which correlation functions for such chiral algebras can be used to compute higher loop form factors in non-supersymmetric 4d quantum field theories.
 

Andrea Puhm
University of Amsterdam

Asymptotic Symmetries and Log Soft Theorems in Gauge Theories and Gravity

Key to a celestial holographic correspondence is the identification of all symmetries. Perturbative quantum gravity was shown to be governed by the infinite-dimensional $w_{1+\infty}$ symmetry which arises from the tower of tree-level soft graviton theorems. How do quantum (loop) effects affect the classical (tree-level) symmetry interpretation? Aside from the leading soft theorems which are all-loop exact, subleading ones receive quantum corrections with logarithmic dependence on the energy of the soft particle. In this talk, I will initiate a program to compute quantum corrections to the charges that generate the asymptotic symmetries in scalar QED and perturbative quantum gravity and show that their conservation corresponds precisely to the leading universal logarithmic soft theorems. I will comment on the fate of the $w_{1+\infty}$ symmetry algebra at the quantum level.
 

Ana-Maria Raclariu
King’s College London & University of Amsterdam

What Can We Learn About Celestial Holography from Ads/CFT?

It is well known that perturbative scattering amplitudes in Minkowski spacetime can be obtained from a flat space limit of AdS-Witten diagrams. Moreover, certain conjectured properties of scattering amplitudes can be derived in a related limit from known properties of CFT correlation functions. In most cases, these results concern the scattering of massive particles. In this talk, I will show that many properties of massless celestial amplitudes similarly arise in certain kinematic limits of correlation functions of local, unitary CFTs in one higher dimension. I will present some concrete examples of celestial amplitudes constructed in this way and derive the infinity of celestial symmetries from Ward identities in the higher dimensional CFT.
 

Atul Sharma
Harvard University

A Celestial Dual for MHV Amplitudes

Atul Sharma will describe recent work on coupling a large-N chiral algebra to the semiclassical limit of Liouville theory to reproduce 4D gluon MHV amplitudes as correlators of 2D light operators. The correlators will produce certain building blocks called “leaf amplitudes”, and Sharma will explain how to recombine them into standard translationally invariant celestial amplitudes.
 

Andy Strominger
Harvard University

Celestial Holography: Past, Present and Future

The ongoing endeavor to realize the holographic principle for quantum gravity in nearly asymptotically flat spacetimes like the one we inhabit is described and motivated. Some highlights of this endeavor are presented, along with some open questions.

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

Group A – PIs and Speakers
The foundation will arrange and pay for all air and train travel to the conference as well as hotel accommodations and reimbursement of local expenses. Business-class or premium economy airfare will be booked for all flights over five hours.

Group B – Funded Participants
The foundation will arrange and pay for all air and train travel to the conference as well as hotel accommodations and reimbursement of local expenses. Economy-class airfare will be booked for all flights.

Group C – Unfunded Participants
Individuals in Group C will not receive funding to attend the meeting. Group C participants may take part in all conference-hosted meals at no additional cost.

Group D – Remote Participants
Individuals in Group D will participate in the meeting remotely. Please register at the link above and a remote participation link will be sent to you approximately two weeks prior to the meeting.

Air and Rail
For individuals in Groups A and B the foundation will arrange and pay for round-trip travel from their home city to the conference.

All travel and hotel arrangements must be booked through the Simons Foundation’s preferred travel agency.

Travel specifications, including preferred airline, will be accommodated provided that these specifications are reasonable and within budget.

Travel arrangements not booked through the preferred agency, including triangle trips and routing/preferred airlines outside budget, must be pre-approved by the Simons Foundation and a reimbursement quote must be obtained through the foundation’s travel agency.

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 James NoMad Hotel 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
Participants in Groups A & B who require accommodations are hosted by the foundation for a maximum of three nights at The James NoMad Hotel. Any additional nights are at the attendee’s own expense. To arrange accommodations, please register at the link above.

The James NoMad Hotel
22 E 29th St
New York, NY 10016
(between 28th and 29th Streets)
https://www.jameshotels.com/new-york-nomad/

For driving directions to The James NoMad, please click here.

Overview
Individuals in Groups A & B 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 as a result of meetings not directly related to the Simons Foundation-hosted meeting (a satellite collaboration 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 and itemized receipts are required for expenses over $24 USD. The foundation DOES NOT provide a meal per diem and only reimburses actual meal expenses.

• Meals taken on travel days are reimbursable.
• Meals taken outside those provided by the foundation (breakfast, lunch, breaks and/or dinner) are not reimbursable.
• If a meal was not provided on a meeting day, dinner for example, that expense is reimbursable.
• Meals taken on days not associated with Simons Foundation-coordinated events are not reimbursable.
• Minibar expenses are not reimbursable
• Meal expenses for a non-foundation guest are not reimbursable.

Group meals consisting of fellow meeting participants paid by a single person will be reimbursed up to $65 per person per meal and the amount will count towards each individual’s $125 daily meal limit.

Ground Transportation
Expenses for ground transportation will be reimbursed for travel days (i.e. traveling to/from the airport) as well as local transportation. While in NYC, individuals are encouraged to use public transportation and not use taxi, Uber or Lyft services.

Attendance
In-person participants and speakers are expected to attend all meeting days. Partial participation is permitted so long as the individual fully attends the first day, which is typically Thursday for two-day meetings. Participants receiving hotel and travel support wishing to arrive on meeting days which conclude at 2:00 PM will be asked to attend remotely.

COVID-19 Vaccination
Individuals accessing Simons Foundation and Flatiron Institute buildings must be fully vaccinated against COVID-19.

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.

Registration and Travel Assistance
Ovation Travel Group
[email protected]
(917) 408-8384 (24-Hours)
www.ovationtravel.com

Meeting Questions and Assistance
Meghan Fazzi
Manager, Events and Administration, MPS, Simons Foundation
[email protected]
(212) 524-6080