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Joint BHI/CMSA Conference on Flat Holography

June 21, 2022 @ 9:00 am - June 24, 2022 @ 5:00 pm

On June 21–24, 2022, the Harvard Black Hole Initiative and the CMSA hosted the Joint BHI/CMSA Conference on Flat Holography (and related topics).

The recent discovery of infinitely-many soft symmetries for all quantum theories of gravity in asymptotically flat space has provided a promising starting point for a bottom-up construction of a holographic dual for the real world. Recent developments have brought together previously disparate studies of soft theorems, asymptotic symmetries, twistor theory, asymptotically flat black holes and their microscopic duals, self-dual gravity, and celestial scattering amplitudes, and link directly to AdS/CFT.

The conference was held in room G10 of the CMSA, 20 Garden Street, Cambridge, MA.


  • Daniel Kapec, CMSA
  • Andrew Strominger, BHI
  • Shing-Tung Yau, Harvard & Tsinghua

Confirmed Speakers:

  • Nima Arkani-Hamed, IAS
  • Shamik Banerjee, Bhubaneswar, Inst. Phys.
  • Miguel Campiglia, Republica U., Montevido
  • Geoffrey Compere, Brussels
  • Laura Donnay, Vienna
  • Netta Engelhardt, MIT
  • Laurent Freidel, Perimeter
  • Alex Lupsasca, Princeton
  • Juan Maldacena, IAS
  • Lionel Mason, Oxford
  • Natalie Paquette, U. Washington
  • Sabrina Pasterski, Princeton/Perimeter
  • Andrea Puhm, Ecole Polytechnique
  • Ana-Maria Raclariu, Perimeter
  • Marcus Spradlin, Brown
  • Tomasz Taylor, Northeastern
  • Herman Verlinde, Princeton
  • Anastasia Volovich, Brown
  • Bin Zhu, Northeastern

Short talks by: Gonçalo Araujo-Regado (Cambridge), Adam Ball (Harvard), Eduardo Casali (Harvard), Jordan Cotler (Harvard), Erin Crawley (Harvard), Stéphane Detournay (Brussels), Alfredo Guevara (Harvard), Temple He (UC Davis), Elizabeth Himwich (Harvard), Yangrui Hu (Brown), Daniel Kapec (Harvard), Rifath Khan (Cambridge), Albert Law (Harvard), Luke Lippstreu (Brown), Noah Miller (Harvard), Sruthi Narayanan (Harvard), Lecheng Ren (Brown), Francisco Rojas (UAI), Romain Ruzziconi (Vienna), Andrew Strominger (Harvard), Adam Tropper (Harvard), Tianli Wang (Harvard), Walker Melton (Harvard)


Monday, June 20, 2022

7:00–9:00 pm Welcome Reception at Andy’s residence


Tuesday, June 21, 2022

9:00–9:30 am Breakfast light breakfast provided
Morning Session Chair: Dan Kapec
9:30–10:00 am Herman Verlinde Title: Comments on Celestial Dynamics
10:00–10:30 am Juan Maldacena Title: What happens when you spend too much time looking at supersymmetric
black holes?
10:30–11:00 Coffee break
11:00–11:30 am Miguel Campiglia Title: Asymptotic symmetries and loop corrections to soft theorems
11:30–12:00 pm Geoffrey Compere Title: Metric reconstruction from $Lw_{1+\infty}$ multipoles

Abstract: The most general vacuum solution to Einstein’s field equations with no incoming radiation can be constructed perturbatively from two infinite sets of canonical multipole moments, which are found to be exchanged under gravitational electric-magnetic duality at the non-linear level. We demonstrate that in non-radiative regions such spacetimes are completely determined by a set of conserved celestial charges, which uniquely label transitions among non-radiative regions caused by radiative processes. The algebra of the conserved celestial charges is derived from the real $Lw_{1+\infty}$ algebra. The celestial charges are expressed in terms of multipole moments, which allows to holographically reconstruct the metric in de Donder, Newman-Unti or Bondi gauge outside of sources.

12:00–2:00 pm Lunch break
Afternoon Session Chair: Eduardo Casali
2:00–2:30 pm Natalie Paquette Title: New thoughts on old gauge amplitudes
2:30–3:00 pm Lionel Mason Title: An open sigma model for celestial gravity

Abstract: A global twistor construction for conformally self-dual split signature metrics on $S2\times S2$  was developed 15 years ago by Claude LeBrun and the speaker.  This encodes the conformal metric into the location of a finite deformation of the real twistor space inside the flat complex twistor space, $\mathbb{CP}3$. This talk adapts the construction to construct global SD Einstein metrics from conformal boundary data and perturbations around the self-dual sector.  The construction entails determining a family of holomorphic discs in $\mathbb{CP}3$ whose boundaries lie on the deformed real slice and the (chiral) sigma model controls these discs in the Einstein case and provides amplitude formulae.

3:00–3:30 pm Coffee break
3:30–4:30 pm Short Talks Daniel Kapec: Soft Scalars and the Geometry of the Space of Celestial CFTs

Albert Law: Soft Scalars and the Geometry of the Space of Celestial CFTs

Sruthi Narayanan: Soft Scalars and the Geometry of the Space of Celestial CFTs

Stéphane Detournay: Non-conformal symmetries and near-extremal black holes

Francisco Rojas: Celestial string amplitudes beyond tree level

Temple He: An effective description of energy transport from holography

4:30–5:00 pm Nima Arkani-Hamed (Dual) surfacehedra and flow particles know about strings


Wednesday, June 22, 2022

9:00–9:30 am Breakfast light breakfast provided
Morning Session Chair: Alfredo Guevara
9:30–10:00 am Laurent Freidel Title: Higher spin symmetry in gravity

Abstract: In this talk, I will review how the gravitational conservation laws at infinity reveal a tower of symmetry charges in an asymptotically flat spacetime.
I will show how the conservation laws, at spacelike infinity, give a tower of soft theorems that connect to the ones revealed by celestial holography.
I’ll present the expression for the symmetry charges in the radiative phase space, which opens the way to reveal the structure of the algebra beyond the positive helicity sector. Then, if time permits I’ll browse through many questions that these results raise:
such as the nature of the spacetime symmetry these charges represent, the nature of the relationship with multipole moments, and the insights their presence provides for quantum gravity.

10:00–10:30 am Ana-Maria Raclariu Title: Eikonal approximation in celestial CFT
10:30–11:00 am Coffee break
11:00–11:30 am Anastasia Volovich Title: Effective Field Theories with Celestial Duals
11:30–12:00 pm Marcus Spradlin Title: Loop level gluon OPE’s in celestial holography
12:00–2:00 pm Lunch break
Afternoon Session Chair: Chiara Toldo
2:00–2:30 pm Netta Engelhardt Title: Wormholes from entanglement: true or false?
2:30–3:00 pm Short Talks Luke Lippstreu: Loop corrections to the OPE of celestial gluons

Yangrui Hu: Light transforms of celestial amplitudes

Lecheng Ren: All-order OPE expansion of celestial gluon and graviton primaries from MHV amplitudes

3:00–3:30 pm Coffee break
3:30–4:30 pm Short Talks Noah Miller: C Metric Thermodynamics

Erin Crawley: Kleinian black holes

Rifath Khan: Cauchy Slice Holography: A New AdS/CFT Dictionary

Gonçalo Araujo-Regado: Cauchy Slice Holography: A New AdS/CFT Dictionary

Tianli Wang: Soft Theorem in the BFSS Matrix Model

Adam Tropper: Soft Theorem in the BFSS Matrix Model

7:00–9:00 pm Banquet Maharaja Restaurant, 57 JFK Street, Cambridge, MA


Thursday, June 23, 2022

9:00–9:30 am Breakfast light breakfast provided
Morning Session Chair: Jordan Cotler
9:30–10:00 am Laura Donnay Title: A Carrollian road to flat space holography
10:00–10:30 am Andrea Puhm Title: Celestial wave scattering on Kerr-Schild backgrounds
10:30–11:00 am Coffee break
11:00–11:30 am Sabrina Pasterski Title: Mining Celestial Symmetries

Abstract: The aim of this talk is to delve into the common thread that ties together recent work with H. Verlinde, L. Donnay, A. Puhm, and S. Banerjee exploring, explaining, and exploiting the symmetries encoded in the conformally soft sector.

Come prepared to debate the central charge, loop corrections, contour prescriptions, and orders of limits!

11:30–12:00 pm Shamik Banerjee Title: Virasoro and other symmetries in CCFT

Abstract:  In this talk I will briefly describe my ongoing work with Sabrina Pasterski. In this work we revisit the standard construction of the celestial stress tensor as a shadow of the subleading conformally soft graviton.  In its original formulation, we find that there is an obstruction to reproducing the expected $TT$ OPE in the double soft limit. This obstruction is related to the existence of the $SL_2$ current algebra symmetry of the CCFT. We propose a modification to the definition of the stress tensor which circumvents this obstruction and also discuss its implications for the existence of other current algebra (w_{1+\infty}) symmetries in CCFT.

12:00–2:00 pm Lunch break
Afternoon Session Chair: Albert Law
2:00–2:30 pm Tomasz Taylor Title: Celestial Yang-Mills amplitudes and D=4 conformal blocks
2:30–3:00 pm Bin Zhu Title:  Single-valued correlators and Banerjee-Ghosh equations

Abstract:  Low-point celestial amplitudes are plagued with singularities resulting from spacetime translation. We consider a marginal deformation of the celestial CFT which is realized by coupling Yang-Mills theory to a background dilaton field, with the (complex) dilaton source localized on the celestial sphere. This picture emerges from the physical interpretation of the solutions of the system of differential equations discovered by Banerjee and Ghosh. We show that the solutions can be written as Mellin transforms of the amplitudes evaluated in such a dilaton background. The resultant three-gluon and four-gluon amplitudes are single-valued functions of celestial coordinates enjoying crossing symmetry and all other properties expected from standard CFT correlators.

3:00–3:30 pm Coffee break
3:30–4:00 pm Alex Lupsasca Title: Holography of the Photon Ring
4:00–5:30 pm Short Talks Elizabeth Himwich: Celestial OPEs and w(1+infinity) symmetry of massless and massive amplitudes

Adam Ball: Perturbatively exact $w_{1+\infty}$ asymptotic symmetry of quantum self-dual gravity

Romain Ruzziconi: A Carrollian Perspective on Celestial Holography

Jordan Cotler: Soft Gravitons in 3D

Alfredo Guevara: Comments on w_1+\inf

Andrew Strominger: Top-down celestial holograms

Eduardo Casali: Celestial amplitudes as AdS-Witten diagrams

Walker Melton: Top-down celestial holograms


Friday, June 24, 2022

9:00–9:30 am Breakfast
9:30–12:30 pm Open Discussion
12:30–2:30 pm Lunch provided at the BHI



June 21, 2022 @ 9:00 am
June 24, 2022 @ 5:00 pm
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