# FY2020 Annual Report

**Quantum Gravity Unit
Assistant Professor Yasha Neiman**

## Abstract

Yasha with students worked on higher-spin theory and on scattering in de Sitter space, the latter in collaboration with Mirian. Mirian worked on higher-spin interactions with Dorin and with external collaborators. Dorin also continued work on stringy models of hadrons with his previous supervisor. Slava worked on boundary degrees of freedom in topological field theories. Sudip worked on expressing scattering amplitudes in terms of current algebra on the celestial sphere. Aritra worked on cosmology with external collaborators, while pursuing his independent work on the connection between asymptotic symmetries and massless strings.

In March, we hosted a high-profile online workshop on boundary symmetries in flat spacetime, a theme that underlies the work of Aritra, Sudip and Slava.

Adi David graduated. David O’Connell joined as Ph.D. student.

## 1. Staff

- Dr. Mirian Tsulaia, Staff Scientist
- Dr. Sudip Ghosh, Postdoctoral Scholar
- Dr. Vyacheslav Lysov, Postdoctoral Scholar
- Dr. Dorin Weissman, Postdoctoral Scholar
- Dr. Aritra Banerjee, Postdoctoral Scholar
- Lena Hashimoto, Administrative Assistant

## 2. Collaborations

### 2.1 Scattering in the static patch of de Sitter space

- Type of collaboration: Joint research
- Researchers:
- Prof. Yasha Neiman (OIST)
- Dr. Mirian Tsulaia (OIST)
- Emil Albrychiewicz (UC Berkeley)

### 2.2 Interaction vertices for supersymmetric higher-spin theory

- Type of collaboration: Joint research
- Researchers:
- Dr. Mirian Tsulaia (OIST)
- Dr. Dorin Weissman (OIST)
- Prof. Joseph Buchbinder (Tomsk Pedagogical Institute and Tomsk State University)
- Prof. Vladimir Krykhtin (Tomsk Pedagogical Institute)

### 2.3**Higher-spin theories in the lightcone approach**

- Type of collaboration: Joint research
- Researchers:
- Dr. Mirian Tsulaia (OIST)
- Dr. Evgeny Skvortsov (University of Mons)
- Dr. Tung Tran (Albert Einstein Institute, Potsdam)

### 2.4 Non-critical string theory as model for hadrons

- Type of collaboration: Joint research
- Researchers:
- Dr. Dorin Weissman (OIST)
- Prof. Jacob Sonnenschein (Tel Aviv University)

### 2.5 Scattering amplitudes and symmetries on the celestial sphere

- Type of collaboration: Joint research
- Researchers:
- Dr. Sudip Gosh (OIST)
- Dr. Shamik Banerjee (Bhubaneswar Institute of Physics)
- Dr. Partha Paul (Chennai Mathematical Institute)

### 2.6 Validity of estimates for deviation from ɅCDM cosmology

- Type of collaboration: Joint research
- Researchers:
- Dr. Aritra Banerjee (OIST)
- Prof. Eoin O. Colgain (Sogang University)
- Prof. Misao Sasaki (Tokyo University)
- Prof. Shahin Sheikh-Jabbari (IPM, Tehran)

## 3. Activities and Findings

### 3.1 Higher-spin holography beyond boundary locality

In a series of two papers that formed part of Adi David’s Ph.D. thesis, we studied some novel points of view on the holographic duality between 4d higher-spin gravity and 3d vector models.

On one paper, we understood that black-hole-like objects in the bulk theory are described by bilocal operators on the boundary. This is analogous in some ways to the duality between bulk strings and boundary Wilson loops in the more standard, string-theoretic holographic models. We then studied the force between two higher-spin black holes in the bulk, and found that it provides a novel example for the cancellation of short-distance divergences in higher-spin theory.

In the other paper, we contrasted the boundary-local and twistorial perspectives on higher-spin holography. We showed that the two differ in a way that was unexpected way in the literature. We classified this as a clash between higher-spin symmetry and boundary locality, indicating that the non-local features of higher-spin theory extend beyond the bulk non-locality that is usually discussed. On the other hand, we showed that ordinary bulk locality can be replaced by spin-locality, in analogy with recent work on the bulk theory by Vasiliev’s group in Moscow. Finally, we argued that this boundary-spin-local picture is in fact the one best suited for our end goal of understanding holography in de Sitter space.

### 3.2 Scattering in the static patch of de Sitter space

In a series of papers with Emil Albrychiewicz and Mirian Tsulaia (one published, one to appear in FY2021), we studied the scattering problem in the static patch of de Sitter space. This is a fundamental and neglected problem in mathematical physics, extending the standard question of particle scattering in flat spacetime into the cosmological situation of a finite-sized observable region. In the first paper, we developed a toolkit for tackling the scattering problem in general theories, and applied it to the case of a scalar field with cubic interactions. In the second paper, we study Yang-Mills theory, where one can go much further, due to its conformal symmetry at tree level. There, we were able to obtain results for scattering amplitudes with the simplest helicity arrangement (N-1MHV) and arbitrary number of external legs. Furthermore, we developed recursion relations that reduce any tree-level amplitude to these N-1MHV building blocks, dressed by ordinary flat-spacetime amplitudes.

**3.3 Quantum higher-spin theories in the lightcone approach**

Mirian Tsulaia, in collaboration with Evgeny Skvortsov and Tung Tran, has continued his work on interacting higher-spin theories that are consistent at the quantum level. Previously, they described the first such theory – a theory of massless fields in 4 dimensions - by defining the interactions and proving their consistency within the lightcone formulation. In this year’s paper, they applied the same approach to a massive theory in 3 dimensions, which resembles string theory in certain ways. This serves to both extend the range of known consistent higher-spin theories, and to bridge the gap between the higher-spin and string-theoretic approaches to quantum gravity.

**3.4 Scattering amplitudes from current algebra on the celestial sphere**

Sudip Ghosh, in collaboration with Shamik Banerjee and Partha Paul, has brought to maturity his independent research program on scattering amplitudes and asymptotic symmetries in flat spacetime. In a series of papers, they systematically study the MHV sector of scattering amplitudes in gauge theory and gravity, and show how these amplitudes can be reconstructed from symmetry principles using a current algebra on the celestial sphere at infinity. A key component in their approach is the identification between sub-leading soft theorems in the bulk theory and operator product expansions on the celestial sphere. The similarities and differences they find between gauge theory and gravity serve to concretely illustrate the general expectation that ultimately, only gravitational theories should admit a purely holographic description.

**3.5 Degrees of freedom and gauge symmetries on boundary surfaces in topological field theories**

In a recent preprint, Slava Lysov has brought to maturity his ambitious independent research program aimed at elucidating the nature of boundary degrees of freedom in gravity and field theory. This is a subject that has received much attention in recent years, and is characterized by variety of only partially-overlapping definitions and claims. Slava has taken on the formidable task of sorting through these confusions, and combining the various approaches into a coherent picture. For this purpose, he uses concrete examples, which are simple enough to admit a fully rigorous mathematical treatment.

**3.6 Non-critical string theory as a model for hadron physics**

Dorin Weissman, in collaboration with Jacob Sonnenschein, has continued his work on non-critical string theory, i.e. string theory in 4 rather than 10 spacetime dimensions, and its application as a description of hadrons.

In one paper, they made progress on the fundamental issues of quantizing such theories. Specifically, they understood how to handle singular points points at which the string “folds”, by modeling them as massive point particles.

In another paper, they used the insights from their stringy models to decipher the inner structure of certain composite particles newly discovered in the LHCb experiment. They provided support for the conjecture that these new particles are tetraquarks, proposed a particular model for their structure, and made experimental predictions for their excited states and decay channels.

## 4. Publications

### 4.1 Journals

**E. Albrychiewitz**and**Y. Neiman**, "Scattering in the static patch of de Sitter space", PRD 103 (2021) 065014 [arXiv:2012.13584]**A. David**and**Y. Neiman**, "Bulk interactions and boundary dual of higher-spin-charged particles", JHEP 03 (2021) 264 [arXiv:2009.02893]- A. Bagchi,
**A. Banerjee**and S. Chakrabortty, "Rindler Physics on the String Worldsheet", PRL 126 (2021) 031601 [arXiv:2009.01408] - S. Banerjee,
**S. Ghosh**and P. Paul, "MHV graviton scattering amplitudes and current algebra on the celestial sphere", JHEP 02 (2021) 176 [arXiv:2008.04330] - J. Sonnenschein and
**D. Weissman**, "Deciphering the recently discovered tetraquark candidates around 6.9 GeV", Eur.Phys.J.C 81 (2021) 1, 25 [arXiv:2008.01095] **A. David**and**Y. Neiman**, "Higher-spin symmetry vs. boundary locality, and a rehabilitation of dS/CFT", JHEP 2010 (2020) 127 [arXiv:2006.15813]- J. Sonnenschein and
**D. Weissman**, "On the quantization of folded strings in non-critical dimensions", JHEP 12 (2020) 120 [arXiv:2006.14634] - E. Skvortsov, T. Tran and
**M. Tsulaia**, "A Stringy theory in three dimensions and Massive Higher Spins", PRD 102 (2020) 126010 [arXiv:2006.05809] - E. Skvortsov, T. Tran and
**M. Tsulaia**, "More on Quantum Chiral Higher Spin Gravity", PRD 101 (2020) 106001 [arXiv:2002.08487] - S. Banerjee,
**S. Ghosh**and R. Gonzo, "BMS symmetry of celestial OPE", JHEP 2004 (2020) 130 [arXiv:2002.00975] - T. Yang,
**A. Banerjee**and E. O Colgain, "Cosmography and flatΛCDM tensions at high redshift", PRD 102, 123532 (2020) [arXiv:1911.01681] - J. Sonnenschein and
**D. Weissman**, "The scattering amplitude of stringy hadrons: strings with opposite charges on their endpoints", JHEP 07 (2020) 156 [arXiv:1906.00976]

Preprints (4):

**V. Lysov**, "Phase Space on a Surface with Boundary via Symplectic Reduction" [arXiv:2103.13284]- I.L. Buchbinder,V.A. Krykhtin,
**M. Tsulaia**,**D. Weissman**, "Cubic Vertices for N=1 Supersymmetric Massless Higher Spin Fields in Various Dimensions" [arXiv:2103.08231] **A. Banerjee**, E. Ó Colgáin, M. Sasaki, M. M. Sheikh-Jabbari, "Lost in the Log-Polynomial Expansion: Comment on arXiv:2101.08278" [arXiv:2102.02098]- S. Banerjee and
**S. Ghosh**, "MHV Gluon Scattering Amplitudes from Celestial Current Algebras" [arXiv:2011.00017]

### 4.2 Books and other one-time publications

Nothing to report

### 4.3 Oral and Poster Presentations

- Neiman, Y. and David, A. “Higher-spin symmetry vs. boundary locality, and a rehabilitation of dS/CFT”.
*Locality vs. higher-spin symmetry on the boundary of de Sitter space*, Higher Spin Gravity Online Seminar, University of Mons, Belgium, March 22 (2021). - Ghosh, S. and Banerjee, S. “MHV gluon scattering amplitudes from celestial current algebras”.
*MHV gluon scattering amplitudes from celestial current algebras*, “Asymptotia” Workshop, OIST, March 15 (2021). - Neiman, Y. “Higher-spin symmetry vs. boundary locality, and a rehabilitation of dS/CFT”.
*Locality vs. higher-spin symmetry on the boundary of de Sitter space*, Lebedev Institute Seminar, Moscow, Russia, March 12 (2021). - Banerjee, A. Bagchi, A. and Chakrabortty, S. “Rindler physics on the string worldsheet”,
*A road to Rindler strings*, Seminar at IIT Mandi, India, March 1 (2021). - Ghosh, S. and Banerjee, S. “MHV gluon scattering from celestial current algebras”.
*MHV gluon & graviton amplitudes from celestial current algebras*, String Theory Webinar, IIT Kanpur, India, February 25 (2021) - Neiman, Y. and Albrychiewicz, E. “Scattering in the static patch of de Sitter space”.
*Scattering in the static patch of de Sitter space*, HEP/GR Colloquium, University of Cambridge, UK, February 3 (2021) - Banerjee, A. Cai, H. Heisenberg, L. O`Colgain E. and Sheikh-Jabbari M.M. “Hubble sinks in the low-redshift swampland”,
*String theory and the H0-ly tension*, Seminar at IIT Gandhinagar, India, January 23 (2021) - Ghosh, S. Banerjee, S. and Paul P. “MHV scattering amplitudes and current algebra on celestial sphere”.
*MHV graviton amplitudes from celestial current algebras*, High Energy Physics seminar, IIS Bangalore, India, January 15 (2021) - Ghosh, S. and Banerjee, S. “MHV gluon scattering from celestial current algebras”.
*Celestial amplitudes in gauge theory and gravity*, Theoretical Physics journal club, University of Porto, Portugal, January 6 (2021) - Neiman, Y. and David, A. “Bulk interactions and boundary dual of higher-spin-charged particles”.
*Geodesic Witten diagrams at the heart of higher-spin theory*, Seminar at National Taiwan University, Taipei, December 18 (2020). - Weissman, D. and Sonnenschein, J. “On the quantization of folded strings in non-critical dimensions”.
*On the quantization of folded strings in non-critical dimensions*, Seminar at YITP, Kyoto, Japan, November 27 (2020) - Ghosh, S. and Banerjee, S. “MHV gluon scattering from celestial current algebras”.
*MHV gluon & graviton amplitudes from celestial current algebras*, Strings and Fields workshop, YITP, Kyoto, Japan, November 10 (2020) - Tsulaia, M. Skvortsov, E. and Tran, T. “Quantum chiral higher spin gravity”,
*Higher spin interactions: from classical to quantum*, Higher Spin Gravity Online Seminar, University of Mons, Belgium, November 3 (2020) - Neiman, Y. and David, A. “Bulk interactions and boundary dual of higher-spin-charged particles”.
*Higher-spin holography beyond boundary locality*, Higher Spin Gravity Online Seminar, University of Mons, Belgium, October 20 (2020) - Neiman, Y. David, A. and Fischer, N. “Spinor-helicity variables for cosmological horizons in de Sitter space”.
*Scattering amplitudes for dS observers*, Workshop on Cosmological Correlators, CERN, September 8 (2020) - Ghosh, S. Banerjee, S. and Paul P. “MHV scattering amplitudes and current algebra on celestial sphere”.
*MHV scattering amplitudes and current algebra on celestial sphere*, Conference on Recent Developments in S-matrix Theory, ICTS-TIFR, Bangalore, India, July 28 (2020) - Weissman, D. and Sonnenschein, J. “On the quantization of folded strings in non-critical dimensions”.
*On the quantization of folded strings in non-critical dimensions*, Seminar at Tel Aviv University, Israel, June 18 (2020) - Tsulaia, M. Angelantonj C. and Florakis I. “Universality of gauge thresholds in non-supersymmetric heterotic vacua”.
*Calculation of gauge thresholds in heterotic compactifications*, Mathematics Seminar, University of Liverpool, UK, June 16 (2020) - Weissman, D. and Sonnenschein, J. “On the quantization of folded strings in non-critical dimensions”.
*On the quantization of folded strings in non-critical dimensions*, Seminar at Nagoya University, Japan, June 15 (2020) - Tsulaia, M. and Sorokin, D. “Supersymmetric reducible higher-spin multiplets in various dimensions”.
*Supersymmetric reducible higher spin multiplets in various dimensions*, Theoretical Physics Seminar, Joint Institute for Nuclear Research, Dubna, Russia, June 2 (2020)

## 5. Intellectual Property Rights and Other Specific Achievements

Nothing to report

## 6. Meetings and Events

### 6.1**“Asymptotia” online workshop**

- Date: March 15-18, 2021
- Venue: OIST Campus Lab 4, Zoom
- Speakers:
- Dr. Sudip Ghosh (OIST)
- Prof. Andrew Strominger (Harvard)
- Dr. Sabrina Pasterski (Princeton)
- Prof. Arjun Bagchi (IIT Kanpur)
- Prof. Daniel Grumiller (TU Wien)
- Prof. Glenn Barnich (UL Brussels)
- Prof. Stephan Stieberger (Max Planck, Munich)
- Dr. Temple He (UC Davis)
- Monica Pate (Harvard)
- Dr. Geoffrey Compere (UL Brussels)
- Prof. Abhay Ashtekar (Penn State)
- Prof. Marc Henneaux (UL Brussels)

### 6.2**“Celestial amplitudes and BMS algebra”**

- Date: January 18, 2021
- Venue: OIST Campus Lab 4, Zoom
- Speakers: Prof. Angelos Fotopoulos (Northeastern University and Wentworth Institute of Technology)

**6.3 “Twistors and the Standard Model”**

- Date: September 24, 2020
- Venue: OIST Campus Lab 4, Zoom
- Speaker: Prof. Peter Woit (Columbia University)

**6.4 “Novel perspectives in string phenomenology”**

- Date: June 1, 2020
- Venue: Zoom
- Speaker: Prof. Alon Faraggi (University of Liverpool)

**6.5 “Domain walls of N=1, D=4 Super Yang Mills theory”**

- Date: May 25, 2020
- Venue: Zoom
- Speaker: Prof. Dmitri Sorokin (University of Padua)

## 7. Other

Nothing to report.