# FY2021 Annual Report

Quantum Gravity Unit
Assistant Professor Yasha Neiman

## Abstract

In FY2021, we worked on higher-spin gravity, scattering in de Sitter space, flat-spacetime holography, Carrollian field theories, mirror symmetry via tropical geometry, holographic description of QCD scattering, cubic interactions in supersymmetric theories from a higher-spin approach, foundations of quantum mechanics, and supersymmetry for solving quantum-mechanical potentials in a discretized setting.

## 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
• Dr. Ardak Kussainova, Postdoctoral Scholar

## 2. Collaborations

### 2.1 Gluon scattering in the de Sitter static patch

• Description: Collaboration resulting from an OIST internship.
• Type of collaboration: Joint research
• Researchers:
• Emil Albrychiewicz, UC Berkeley
• Prof. Yasha Neiman, OIST
• Dr. Mirian Tsulaia, OIST

### 2.2 Supersymmetric cubic interactions from higher-spin approach

• Description: Continued collaboration from previous FY
• 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 Supersymmetric approach to discrete-time Schrodinger equation

• Description: Inter-unit collaboration within OIST
• Type of collaboration: Joint research
• Researchers:
• Dr. Mirian Tsulaia, OIST Quantum Gravity Unit
• Dr. Jonas Sonnenchein, OIST Theory of Quantum Matter Unit

### 2.4 Mirror symmetry from tropical geometry

• Type of collaboration: Joint research
• Researchers:
• Dr. Vyacheslav Lysov, OIST
• Prof. Andrei Losev, National Research University Higher School of Economics, Moscow

### 2.5 String and field theory in the Carrollian limit

• Type of collaboration: Joint research
• Researchers:
• Dr. Aritra Banerjee, OIST
• Prof. Arjun Bagchi, IIT Kanpur
• Prof. Shankhadeep Chakrabortty, IIT Ropar
• Dr. Kedar S. Kolekar, IIT Kanpur
• Sudipta Dutta, IIT Kanpur
• Punit Sharma, IIT Kanpur
• Ritankar Chatterjee, IIT Kanpur

### 2.6 Holographic description of hadron scattering

• Type of collaboration: Joint research
• Researchers:
• Dr. Dorin Weissman, OIST
• Prof. Jacob Sonnenschein, Tel Aviv University
• Prof. Massimo Bianchi, Rome University Tor Vergata
• Dr. Maurizio Ferrotta, National Institute for Nuclear Physics, Rome

### 2.7 Scattering amplitudes and symmetry algebras on the celestial sphere

• Type of collaboration: Joint research
• Researchers:
• Dr. Sudip Ghosh, OIST
• Dr. Shamik Banerjee, Bhubaneswar Institute of Physics
• Dr. Partha Paul, Chennai Mathematical Institute
• Sai Satyam Samal, Homi Bhabha National Institute, Mumbai

## 3. Activities and Findings

### 3.1 New diagrammatic rules for higher-spin gravity

Higher-spin gravity is an important object in mathematical physics, forming an intermediate between field theories (including General Relativity) and string theory. In recent years, the theory’s development has run into difficulties due to a failure of locality, which was observed in calculations of the 4-point scalar correlator. This year, in collaboration with Slava Lysov, I understood how to resolve this issue, by introducing a new, more string-like formulation of the theory. This new formulation constructs a propagator out of the Didenko-Vasiliev “black hole” solution, which thus acts as higher-spin gravity’s analogue of the fundamental string. By studying cubic interaction diagrams involving the Didenko-Vasiliev solution, we showed that the non-locality of the 4-point scalar correlator is resolved. The relevant results should appear as a series of 3 papers in FY2022.

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

In a paper with Emil Albrychiewicz and Mirian Tsulaia, 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 paper, we study this problem in the context of tree-level Yang-Mills theory. 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.
In subsequent work (to appear in FY2022), I studied N-1MHV de Sitter scattering amplitudes for gravity, using Kirill Krasnov’s new formulation of General Relativity. While Krasnov’s new formalism has been used previously to recover known results, my work constitutes its first application to a previously unsolved problem.

### 3.3 Scattering amplitudes from current algebra on the celestial sphere

Sudip Ghosh, in collaboration with Shamik Banerjee, 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.

### 3.4 Mirror symmetry in tropical geometry

Mirror symmetry is a rich topic in mathematical physics, in which string theory is applied to study the topology of complex 3-dimensional manifolds. Slava Lysov, in collaboration with Andrei Losev, found a simpler way to calculate the same topological quantities, by reducing from ordinary complex numbers to so-called tropical numbers. Instead of string theory, the topological invariants are then described by supersymmetric quantum mechanics on graphs. The results are now published in a preprint. Aside from providing a simpler setup for computations, the quantum mechanics on graphs hints at an underlying quantum field theory. This theory, and its locality properties, should make a fruitful subject for future work.

### 3.5 Higher-spin and lower-spin supersymmetric cubic interactions

Mirian Tsulaia and Dorin Weissman, in collaboration with I.L. Bukhbinder and V.A. Krykhtin, have published an analysis of possible cubic interactions in supersymmetric higher-spin theories in various spacetime dimensions, following a BRST approach. Their results shed new light on the interaction structure of familiar lower-spin theories as well, such as supersymmetric Yang-Mills theory and supergravity.

### 3.6 Holographic description of hadron scattering

Dorin Weissman, in collaboration with Massimo Bianchi and Jacob Sonnenschein, wrote a preprint (journal publication in FY2022) on string-theoretic models for hadrons, in particular within AdS/CFT. They calculated hadron scattering processes, comparing with experimental data. They focused on a regime that is difficult for the stringy models to reproduce: the regime of high-energy (so-called “deep”) scattering, in which real-world hadrons reveal their quark inner structure. By carrying out these calculations, they were thus able to identify the limits of validity of the stringy models.

### 3.7 Supersymmetry as a tool for discrete-time quantum mechanics

In quantum mechanics, N=2 supersymmetry can be introduced as a general technique for solving the Schrodinger equation in integrable systems. This works by constructing a hierarchy of supersymmetry-related Hamiltonians whose ground states correspond to all the energy states of the original system. This year, Mirian Tsulaia collaborated with Jonas Sonnenschein (Theory of Quantum Matter Unit) on adapting this technique to systems where time had been discretized into finite steps. They accomplished this by showing how the method of “exact discretization” – a way of defining discrete versions of differential operators – can be extended to the supersymmetry algebra.

### 3.8 Carrollian limit of string and field theory

Aritra Banerjee wrote a series of preprints in collaboration with Arjun Bagchi’s group (one already published in FY2022). The subject of their work was the so-called Carrollian limit of string and field theories: the limit in which the speed of light goes to zero. This arises naturally in two contexts: at the lightlike boundary of flat spacetime, and on the worldsheet of strings in the tensionless limit of string theory. In his work, Aritra related these two contexts to each other, linking tensionless string with flat-spacetime holography in 3 spacetime dimensions. Then, in the latest preprint, he began a general study of field theories with Carrollian structure, in order to map out the space of possible boundary theories in flat-spacetime holography.

### 3.9 Measurement postulates of quantum mechanics

Stepping outside our usual research field, Slava Lysov and I wrote a preprint on the foundations of quantum mechanics. We formulated a model for how the basic properties of quantum-mechanical measurement can arise from the structure of Hilbert spaces and unitary evolution, much like thermodynamics arises from statistical mechanics. Our model is a hybrid of existing approaches, specifically the frequentist approach to the Born rule and the decoherence approach to the measurement process. Its virtue is in presenting all the properties of measurement in a single, concise and simple setup, and in a language that is accessible to practicing quantum physicists, as opposed to “foundations” specialists.

## 4. Publications

### 4.1 Journals

1. Albrychiewicz, E., Neiman, Y., Tsulaia, M. “MHV amplitudes and BCFW recursion for Yang-Mills theory in the de Sitter static patch”. Journal of High Energy Physics, doi: 10.1007/JHEP09(2021)176 (2021).
2. Buchbinder, IL., Krykhtin, VA., Tsulaia, M., Weissman, D. “Cubic vertices for N=1 supersymmetric higher spin fields in various dimensions”. Nuclear Physics B, doi: 10.1016/j.nuclphysb.2021.115427 (2021).
3. Banerjee, S., Ghosh, S., “MHV gluon scattering amplitudes from celestial current algebras”. Journal of High Energy Physics,
doi: 10.1007/JHEP10(2021)111 (2021).
4. Banerjee, S., Ghosh, S., Samal, SS. “Subsubleading soft graviton symmetry and MHV graviton scattering amplitudes”. Journal of High Energy Physics,
doi: 10.1007/JHEP08(2021)067 (2021).
5. Banerjee, A., Colgain, EO., Sasaki, M., Sheikh-Jabbari, MM., Yang, T. “On problems with cosmography in the dark ages”. Physics Letters B,
doi: 10.1016/j.physletb.2021.136366 (2021).

### 4.2 Books and other one-time publications

Nothing to report

### 4.3 Oral and Poster Presentations

1. Albrychiewicz, E., David, A., Fischer, N., Neiman, Y., Tsulaia, M., (based on numerous papers). Higher-spin theory in de Sitter (discussion session), Quantum Features in a de Sitter Universe workshop, Corfu Institute, Greece, September 14 (2021).
2. David, A., Neiman, Y. “Bulk interactions and boundary dual of higher-spin-charged particles”. What is the force between two higher-spin black holes, Quarks 2020 workshop on Integrability, Holography, Higher Spin Gravity and Strings, Moscow, Russia, June 2 (2021).
3. Bianchi, M., Firrotta, M., Sonnenschein, J., Weissman, D. “Partonic behavior of string scattering amplitudes from holographic models of QCD”. Hard scattering and holographic QCD, seminar at Nagoya University, Japan, January 11 (2022).
4. Bianchi, M., Firrotta, M., Sonnenschein, J., Weissman, D. “Partonic behavior of string scattering amplitudes from holographic models of QCD”. Hard scattering and holographic QCD, seminar at YITP, Kyoto, Japan, December 17 (2021).
5. Buchbinder, IL., Krykhtin, VA., Tsulaia, M., Weissman, D. “Cubic vertices for N=1 supersymmetric higher spin fields in various dimensions”. Cubic vertices for supersymmetric higher spin fields, Strings and Fields 2021 workshop, YITP, Kyoto, Japan, August 27 (2021).
6. Bagchi, A., Banerjee, A., Dutta, S., Kolekar, KS., Sharma, P. “Carroll covariant scalar fields in two dimensions”, The curious case of Carrollian theories, seminar at Kyoto University, Japan, March 23 (2022).
7. Banerjee, A. Cai, H. Heisenberg, L. OColgain E. and Sheikh-Jabbari M.M. “Hubble sinks in the low-redshift swampland”, String theory and the H0-ly tension, Sabarmati lecture series, IIT Gandhinagar, India, July 9 (2021).
8. Banerjee, A. Cai, H. Heisenberg, L. OColgain E. and Sheikh-Jabbari M.M. “Hubble sinks in the low-redshift swampland”, The cosmic expansion conundrum: can quintessence help at all?, OIST Researcher Appreciation Month poster session, July 2021.
9. Bagchi, A., Banerjee, A., Chakrabortty, S. "Rindler Physics on the String Worldsheet". Rindler physics on the worldsheet, seminar at Kyoto University, Japan, October 27 (2021).
10. Bagchi, A., Banerjee, A., Chakrabortty, S. "Rindler Physics on the String Worldsheet". Rindler physics on the worldsheet, String Theory and Quantum Gravity conference at YITP, Kyoto, Japan, December 13 (2021).
11. Bagchi, A., Banerjee, A., Chakrabortty, S. "Rindler Physics on the String Worldsheet". Rindler physics on the worldsheet, Indian Strings Meeting, IIT Roorkee, India, December 13 (2021).
12. Bagchi, A., Banerjee, A., Chakrabortty, S. "Rindler Physics on the String Worldsheet". Rindler physics on the worldsheet, seminar at Peking University, China, January 7 (2021).
13. Buchbinder, IL., Krykhtin, VA., Tsulaia, M., Weissman, D. “Cubic vertices for N=1 supersymmetric higher spin fields in various dimensions”. Supersymmetric cubic interactions for lower spins from “higher spin” approach, Aspects of Symmetry RDP PhD school and workshop, Tbilisi State University, Georgia, November 8-12 (2021).
14. Buchbinder, IL., Krykhtin, VA., Tsulaia, M., Weissman, D. “Cubic vertices for N=1 supersymmetric higher spin fields in various dimensions”. Supersymmetric cubic interactions for lower spins from “higher spin” approach, Quarks 2020 workshop on Integrability, Holography, Higher Spin Gravity and Strings, Moscow, Russia, May 31-June 5 (2021).
15. Buchbinder, IL., Krykhtin, VA., Tsulaia, M., Weissman, D. “Cubic vertices for N=1 supersymmetric higher spin fields in various dimensions”. Free and interacting higher spin supermultiplets in various dimensions, seminar at Tokyo Institute of Technology, Japan, April 21 (2021).
16. Buchbinder, IL., Krykhtin, VA., Tsulaia, M., Weissman, D. “Cubic vertices for N=1 supersymmetric higher spin fields in various dimensions”. Free and interacting higher spin supermultiplets in various dimensions, seminar at Joint Institute for Nuclear Research, Dubna, Russia, November 15 (2021).

## 5. Intellectual Property Rights and Other Specific Achievements

Nothing to report

## 6. Meetings and Events

### 6.1 Carrollian and Galilean conformal higher spin algebras in any dimension

• Date: November 25, 2021
• Venue: OIST Campus Lab4 and Zoom
• Speaker: Dr. Andrea Campoleoni (Universite de Mons)

### 6.2 The Festina Lente bound and some applications

• Date: November 17, 2021
• Venue: OIST Campus Lab4 and Zoom
• Speaker: Prof. Thomas van Riet (KU Leuven)

### 6.3 Carroll symmetry and cosmology

• Date: October 20, 2021
• Venue: OIST Campus Lab4 and Zoom
• Speaker: Dr. Jelle Hartong (University of Edinburgh)

### 6.4 Duality-symmetric formulation of electrodynamics and (chiral) p-form generalizations

• Date: October 13, 2021
• Venue: OIST Campus Lab4 and Zoom
• Speaker: Dr. Karapet Mkrtchyan (Imperial College London)

### 6.5 On broken supersymmetry in string theory

• Date: October 6, 2021
• Venue: OIST Campus Lab4 and Zoom
• Speaker: Prof. Augusto Sagnotti (Scuola Normale Superiore)

### 6.6  Flat holography as a flat limit of AdS/CFT

• Date: September 1, 2021
• Venue: OIST Campus Lab4 and Zoom
• Speaker: Dr. Eliot Hijano (Princeton University)

### 6.7 Yang-Baxter sigma models from 4D Chern-Simons theory

• Date: August 25, 2021
• Venue: OIST Campus Lab4 and Zoom
• Speaker: Prof. Kentaroh Yoshida (Kyoto University)

### 6.8  Flat holography and BMSFT

• Date: July 5, 2021
• Venue: OIST Campus Lab4 and Zoom
• Speaker: Prof. Wei Song (Tsinghua University)

### 6.9 Fluxes and charges in an expanding Universe

• Date: June 14, 2021
• Venue: OIST Campus Lab4 and Zoom
• Speaker: Prof. Marika Taylor (University of Southampton)

### 6.10 Towards a ghost-free theory of quantum gravity

• Date: May 18, 2021
• Venue: OIST Campus Lab4
• Speaker: Dr. Luca Buoninfante (Tokyo Institute of Technology)

### 6.11 Cluster integrable systems and supersymmetric gauge theories

• Date: April 26, 2021
• Venue: OIST Campus Lab4 and Zoom
• Speaker: Prof. Andrei Marshakov (Skoltech, Higher School of Economics, ITEP, Lebedev Physics Institute)

### 6.12 Null boundary symmetries

• Date: April 12, 2021
• Venue: OIST Campus Lab4 and Zoom
• Speaker: Prof. Shahin Sheikh-Jabbari (IPM Tehran)

### 6.13 Enhanced gauge symmetry and suppressed cosmological constant in heterotic interpolating models

• Date: April 5, 2021
• Venue: OIST Campus Lab4 and Zoom
• Speaker: Prof. Hiroshi Itoyama (NITEP, Osaka City University)

## 7. Other

Nothing to report.