Titles and abstracts

Monday, Sept. 23rd

• 10:00-11:00, Announcements
• 11:30-12:30, Junggi Yoon

Title: Schwarzian Theory, Chaos and Higher Spin

[Slides]

Abstract:

• 14:00-15:00, Yegor Goncharov

Title: Scattering amplitudes as multiparticle higher-spin charges in the correspondence space

Abstract: Multi-particle scattering amplitudes are represented as conserved higher-spin charges by using unfolded dynamics formulation of massless fields. The advantage of the proposed approach is that multi-particle amplitudes acquire the form of an integral of a closed form in the correspondence space unifying usual space-time with the twistor-like spinor space. This allows one to identify seemingly different formulae for amplitudes in terms of twistor and space-time integrals. Example of tree MHV amplitudes of Yang-Mills theory is considered in detail. In these terms all information on the amplitude is contained in a single function that, even for lower-spin amplitudes, can be interpreted as higher-spin symmetry parameter.

[Slides]

Tuesday, Sept. 24th

• 10:00-11:00, Kanghoon Lee

Title: Kerr-Schild double field theory and classical double copy

Abstract: In this talk, I will present a generalization of the conventional KS formalism, which is a powerful tool for constructing exact solutions in general relativity, to double field theory (DFT) and supergravities. I will describe the generalized KS ansatz for the generalized metric in terms of a pair of null vectors and apply this ansatz to the equations of motion of DFT. I'll show that it is possible to find solutions by considering linear equations only. Based on this formalism, I'll discuss that the classical double copy structure, which represents solutions of the Einstein equation in terms of solutions of the Maxwell equation, can be extended to the entire massless string NS-NS sector.

[Slides]

• 11:30-12:30, Yihao Yin

Title: Solving Vasiliev's equations and exploring their physical content

Abstract: In my talk I will briefly introduce the method of solving Vasiliev’s equations (in 4D with only integer spins) by using the holomorphic gauge. I will elaborate on how to find suitable initial data such that the resulting solutions at the linearized level describe perturbative fields with desirable symmetry properties on an (A)dS background. Two examples in dS and AdS respectively will be shown, and some recent attempt to generalize the construction of quantum systems in the holomorphic gauge will be further discussed.

[Slides]

Wednesday, Sept. 25th

• 10:00-11:00, Konstantin Alkalaev

Title: On HS theory in two dimensions

[Slides]

• 11:30-12:30, Daniel Grumiller

Title: Towards flat space higher spin models in two dimensions

Abstract: Since gravity in three and two dimensions does not propagate gravitational waves these dimensions evade many of the no-go results that constrain higher spin theories. In three dimensions interacting flat space higher spin theories emerge from Inonu-Wigner contractions of corresponding AdS theories. In two dimensions the situation is more subtle. I present work in progress showing a path towards flat space higher spin models in two dimensions.

[Slides]

• 14:00-15:00, Justin David

Title: Unitarity and the Chaos bound

Abstract: We study the role of unitarity in various observables in 2d CFTs. We consider 2d CFTs with large central charge in an excited state obtained by the insertion of an operator of large conformal dimensions at spatial infinities in the thermal state.

We show that there is a violation of the chaos bound whenever the operator has negative conformal dimensions. We present a specific realisation of this situation in the holographic Chern-Simons formulation of a CFT with W₃⁽²⁾ symmetry also known as the Bershadsky-Polyakov algebra. We then study the 2d conformal field theories with W₃ symmetry. We show that the unitarity bound on states with higher spin-3 charge ensures that the chaos bound is satisfied as well and the jump in entanglement entropy during local quantum quenches remains real and finite.

[Slides]

• 15:30-16:30, Cheng Peng

Title: SYK, chaos and higher-spins

[Slides]

Thursday, Sept. 26th

• 10:00-11:00, Jeong-Hyuck Park

Title: O(D,D) completion of General Relativity

Abstract: While the initial motivation of Double Field Theory was to reformulate supergravity in an O(D,D) manifest manner, through subsequent further developments, the theory has now evolved into `Stringy Gravity' which assumes the whole massless NS-NS sector as stringy graviton fields. I will review Double Field Theory as Stringy Gravity, or the O(D,D) completion of General Relativity.

[Slides]

• 11:30-12:30, Roberto Bonezzi

Title: Leibniz algebras and the tensor hierarchy

Abstract: Duality covariant formulations of supergravity have a gauge structure that goes beyond Lie algebras. In this talk I will present recent developments concerning the identification of the correct algebraic structure underlying the interactions of towers of p-forms, known as the tensor hierarchy. In particular, this abstract formulation allows to construct gauge covariant curvatures in a completely model-independent way. Finally, I will show how to provide field equations for both the p-forms and scalars in terms of first order duality relations.

• 14:00-15:00, Per Sundell

Title: Topological fields, defects and higher spins

Abstract: We formulate a dual framework for relativistic quantum field theory by adapting an AKSZ inspired version of Atiyah's axioms for topological field theories with defects to noncommutative geometry, stressing the role of Lyakhovich-Sharapov partial boundary actions. We identify observables containing holographic correlation functions in Vasiliev-type higher spin gravities with local degrees of freedom in three and four dimensions. We highlight how various physically interesting objects with different co-dimensions, such as black hole states, domain walls and conical defects arise as geometrically entangled boundary states of flat Quillen superconnections.

Friday, Sept. 27th:

• 10:00-11:00, Kevin Morand

Title: M. Kontsevich’s graph complexes and universal structures on graded symplectic manifolds

Abstract: In the formulation of his celebrated Formality conjecture, M. Kontsevich introduced a universal version of the deformation theory for the Schouten algebra of polyvector fields on affine manifolds. This construction is generalised to graded symplectic manifolds of arbitrary degree n ≥ 1. The corresponding graph model is given by the full Kontsevich graph complex fGC_d where d=n+1 stands for the dimension of the associated AKSZ type σ-model. This generalisation is instrumental to classify universal structures on graded symplectic manifolds. We conclude by discussing the possible rôle played by this new deformation theory regarding the quantization problem for Courant algebroids and higher symplectic Lie-n algebroids.

[Slides]

• 11:30-12:30, Evgeny Skvortsov

Title: Formal Higher Spin Gravity I

Abstract: We discuss how to construct integrable models from associative algebras with application to Formal Higher Spin Gravities (HSGRA): constructing any HSGRA is equivalent to finding a certain deformation of a given higher spin algebra. We present various methods to describe such deformed algebras, discuss how to construct exact solutions and other results. Finally, we point out the relation to Deformation Quantization, topological string theory and propose a consistent scheme that avoids the non-locality problem.

[Slides]

• 14:00-15:00, Alexey Sharapov

Title: Formal Higher Spin Gravity II

Abstract: In the second part we discuss precise relation between strong homotopy algebras and HSGRA and treat interactions as deformations of the underlying A_∞ structure. We also touch on geometrical interpretation of HSGRA models in terms of Lie algebroids/groupoids. Physical observables should be given by invariants and several classes of invariants, including the new ones, are described. We show that the equations of all HSGRA are integrable and an explicit general solution can be constructed with the help of a Lax pair. Finally, we discuss several new HSGRA's that were constructed using these new techniques.

[Slides]

• 15:30-16:30, Dario Francia

Title: On asymptotic symmetries in any dimension

Saturday, Sept. 28th:

• 10:00-11:00, Stefano Giaccari

Title: An effective action approach to higher spin theories in flat spacetime

Abstract: Using the effective action method, we investigate the higher spin actions in flat spacetime that can be obtained by integrating out a fermion field coupled to external higher spin source fields. In particular, an approach based on Weyl-Wigner quantization allows to identify the gauge symmetry of these models and to find the L_∞ structure that characterizes many (classical) field theories, including closed string field theory. This structure is also found to be consistent with a Yang-Mills-like model for master fields. However, when the actions for the component fields are considered, non-locality must be introduced to grant the absence of ghosts at perturbative level.

[Slides]

• 11:30-12:30, Sergei Kuzenko

Title: Superconformal higher spin theories in curved backgrounds

Abstract: This talk will review some of the results obtained in arXiv:1701.00682 and arXiv:1902.08010.

[Slides]

• 14:00-15:00, Michael Ponds

Title: Conformal higher spin fields in curved space: the non-supersymmetric case

Abstract: This talk will review results from the three recent publications arXiv:1902.08010, arXiv:1812.05331 and arXiv:1806.06643.

[Slides]

Monday, Sept. 30th:

• 10:00-11:00, Maxim Grigoriev

Title: Background fields and CHS theories in 3d

[Slides]

• 11:30-12:30, Dario Rosa

Title: The importance of the tail: chaotic/integrable and Hawking-Page phase transitions in SYK-like systems

Abstract: We will discuss some recent results obtained by a careful study of the chaotic properties of various deformations of the SYK model.

In the first part of the talk, we will focus on the mass-deformed SYK model, a variant of SYK which is deformed by a random mass term. We will see that the model displays a transition from chaotic to integrable regime while increasing the strength of the mass term. Such a transition is not homogeneous along the spectrum: the tail of the spectrum, including the ground state and the low lying modes, makes the transition for very small values of the mass deformation, while the highly excited states require strong mass deformations to migrate to the integrable regime. This behavior signals that the chaos/integrable transition is temperature-dependent.

In the second part of the talk, we will discuss the holographic implications of this phenomenon: we will study a two-site SYK-model coupled by a relevant quadratic interaction. Such a model is argued to be holographically dual to a global AdS2 geometry, which displays a Hawking-Page phase transition from a wormhole geometry to a two-site SYK model with a temperature-dependent chaos/integrable transition, like the one described in the first part of the talk.

Hence, we conjecture that a temperature-dependent chaos/integrable transition is dual to a Hawking-Page phase transition in the gravity side.

References:

T. Nosaka, D. Rosa and J. Yoon, “The Thouless time for mass-deformed SYK,” JHEP 1809, 041 (2018) arxiv:1804.09934 [hep-th].

A. M. García-García, T. Nosaka, D. Rosa and J. J. M. Verbaarschot, “Quantum chaos transition in a two-site SYK model to an eternal transversable wormhole,” arxiv:1901.06031 [hep-th].

[Slides]

• 14:00-15:00, Ioannis Papadimitriou

Title: Higher form holography

Abstract: After reviewing the concept of generalized global symmetries in quantum field theory, I will discuss the holographic realization of such symmetries in terms of higher form fields in AdS. In particular, I will describe work in progress aiming to classify the possible boundary conditions for higher form fields, as well as the corresponding asymptotic symmetries and anomalies.

Tuesday, Oct. 1st:

• 10:00-11:00, Yasha Neiman

Title: Higher-spin theory in the de Sitter causal patch

Abstract: I will discuss the problem of an observer's S-matrix in de Sitter space, i.e. the mapping between lightlike field data on the initial and final horizons of a de Sitter static patch. I will show how the S-matrix of the free HS multiplet can be packaged in a spinor-helicity language. This will be done by relating each horizon separately to global, fully HS-invariant data.

I will then argue that HS symmetry prevents any corrections to the free S-matrix, except in the “soft" sector of zero frequencies. This will be done by analyzing (somewhat heuristically) the very slight breaking of HS symmetry due to a choice of horizon.

• 11:30-12:30, Yasuaki Hikida

Title: Matrix-valued higher spin holography

Abstract: Higher spin gravity is believed to describe the tensionless limit of string theory. However, higher spin gravity usually includes only a few gauge fields for each spin, and its degrees of freedom is far from sufficient to describe large number of higher spin states of strings. Matrix-valued extension of higher spin gravity is expected to be useful as in the case that large N Yang-Mills theory would explain infinitely many string states. In this talk, we propose that 3d matrix-valued higher spin gravity is dual to 2d Grassmannian-like coset model. As a check of the proposal, we examine the asymptotic symmetry of higher spin gravity with full quantum corrections and compare it with the symmetry of dual coset model.

[Slides]

• 14:00-15:00, Changhyun Ahn

Title: The N=4 Coset Model and the Higher Spin Algebra

[Slides]

• 15:30-16:30, Taejin Lee

Title: TBA

[Slides]

Wednesday, Oct. 2nd:

• 10:00-11:00, Mikhail Vasiliev

Title: Spin-locality in higher-spin gauge theories

[Slides]

• 11:30-12:30, Olga Gelfond

Title: Spin-Locality of Higher-Spin Theories and Star-Product Functional Classes

[Slides]

• 14:00-15:00, Vyacheslav Didenko

Title: Higher order vertices in HS theory

Abstract: Some higher order vertices up to quintic order are calculated in d=4 HS theory from Vasiliev equations. The results are obtained for any parity breaking parameter of the theory and exhibit remarkable spin-local structure.

[Slides]