Holography and Observables in Quantum Gravity

9 Nov 2026, 09:00 → 13 Nov 2026, 16:00 Asia/Tokyo

Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12) (Riken, Wako)

Overview:

In the past 20 years, there has been significant progress in our understanding of quantum gravity based on AdS/CFT. Recently, study of quantum gravity beyond AdS/CFT attracts a lot of attention, where there is no longer an asymptotically AdS boundary on which we can perform measurements with infinite accuracy. Thus it is important to understand observables in gravitational spacetimes with no asymptotic AdS boundaries, what an observer experiences and measures in such a spacetime,  and what is the microscopic theory that describes them.  This workshop aims to gather researchers in the this subject to exchange cutting edge ideas, aiming to establish new research directions and collaborations.

Registration: closed

Invited speakers:

Sergio Aguilar Gutierrez (OIST, Okinawa)

Jan Boruch (Stanford University)

Keiichiro Furuya (IPMU, Tokyo)

Ping Gao [online] (UCAS, Beijing)

Phillip Hoehn (OIST, Okinawa)

Kristan Jensen (University of Victoria)

Jonah Kudler-Flam [online] (IAS, Princeton)

Yasunori Nomura (UC Berkeley)

Kazumi Okuyama (Shinshu University)

Cheng Peng [online] (UCAS, Beijing)

Moshe Rozali (University of British Columbia)

Shanming Ruan (Peking University)

Martin Sasieta (UC Berkeley)

Tadashi Takayanagi (YITP, Kyoto)

Misha Usatyuk (IAS, Princeton)

Jie-qiang Wu (UCAS, Beijing)

Zhenbin Yang (Tsinghua University)

Mengyang Zhang (IPMU, Tokyo)

Organizers:

Gabriele Di Ubaldo, Satoshi Iso, Masamichi Miyaji, Shigehiro Nagataki, Yasunori Nomura, Tomonori Ugajin

Support:

This workshop is supported by JST ASPIRE program "RIKEN-Berkeley mathematical quantum science initiative" (PI: Tetsuo Hatsuda, Partner PI: Wick Haxton) and by iTHEMS working group Quantum Information & Gravity (QuIG).

Monday 9 November

1 Quantum Gravity in a Universe Without an Outside

Speaker: Yasunori Nomura

11:00 Coffee

2 Relational path integral and quantum frame covariance in gravity

I will present our recent proposal for a relational bundle-geometric formulation of the gravitational path integral by invoking the new tool of quantum reference frames (QRFs), which in gravity are gauge-covariant coordinate systems constructed from the available field content. Formulated in terms of relational (frame-dressed) observables, this yields formally a gauge-invariant path integral without ghosts and anomalies, and in which observables and their correlators are local to a frame. A key feature of it is its built-in covariance under QRF changes: it is a perspective-neutral path integral which encodes all internal QRF perspectives and the transformations between them. This leads to several qualitative predictions: local correlators and time evolution of relational observables in one QRF perspective become fuzzy in another, and a new spectrum of relational vacua arises. Comprised of frame-dependent no-boundary and asymptotic ground states, a vacuum from one perspective appears generally excited in another. Time permitting, I may also comment on how this offers starting point for a relational notion of renormalization. [Based on arXiv:2607.21463 and work in progress.]

Speaker: Philipp Hoehn

12:20 Lunch & Coffee

3 INTEGRABILITY-CHAOS TRANSITION OF THE ADS3 TENSIONLESS STRINGS

Speaker: Cheng Peng

15:00 Coffee

4 Contributed talk

Speaker: Ahmed Abdalla

5 Contributed talk

Speaker: Kotaro Tamaoka

16:20 Coffee

6 Contributed talk

Speaker: Javier Moreno

7 Contributed talk

Speaker: Joydeep Naskar

Tuesday 10 November

8 Matrix model duals of JT gravity multiverses

Speaker: Ping Gao

11:00 Coffee

9 TBA

Speaker: Zhenbin Yang

12:20 Lunch & Coffee

10 TBA

Speaker: Jan Boruch

15:00 Coffee

11 Codimension-Zero Holographic Complexity and Spectral Three-Point Correlators

Holographic complexity is expected to capture the linear growth of black hole interiors, with quantum corrections ultimately leading to a late-time saturation. We develop a spectral formulation of holographic complexity measures associated with codimension-zero bulk regions in the framework of the complexity=anything proposal. The corresponding generating function of complexity is governed by three-point correlation functions of the density of states, establishing a direct connection between bulk geometric observables and nonperturbative Euclidean spacetime wormholes. We find that the codimension-zero holographic complexity reduces to the sum of two codimension-one contributions and exhibits a universal time evolution, characterized by an exponentially long regime of linear growth followed by saturation at the Heisenberg time. The late-time plateau is a direct result of the spectral level repulsion, a generic feature of quantum chaotic systems, thereby providing a universal mechanism for the saturation of holographic complexity. We also develop a complementary operator interpretation, in which Euclidean wormhole corrections render the semiclassical basis of fixed-complexity states overcomplete. Constructing a complete orthonormal basis then yields well-defined holographic complexity operators that reproduce the same universal time evolution. Our results establish a unified connection among black hole interiors, chaotic spectral statistics, and Euclidean wormholes in quantum gravity.

Speaker: Shanming Ruan

16:20 Coffee

Poster session

18:00 Banquet (Hirosawa club)

Wednesday 11 November

12 Runaways in the no-boundary wavefunction

Speaker: Kristan Jensen

11:00 Coffee

13 An SYK wormhole under the microscope

In this talk, I will describe a large-N wormhole saddle in the Sachdev–Ye–Kitaev (SYK) model for the variance of a heavy operator’s thermal one-point function across realizations of the microscopic couplings. I will argue that this saddle describes a double-trumpet geometry. In the double-scaling limit of SYK, the wormhole defines a quantum transition amplitude in an emergent bulk Hilbert space of chords connecting the two boundaries. In the Schwarzian limit, these chords proliferate, giving a transition amplitude in the open-universe Hilbert space of Jackiw–Teitelboim (JT) gravity. Comparing the SYK and JT amplitudes provides a direct test of heavy-operator randomness in SYK. Time permitting, I will discuss the bulk structure of the half-wormhole for a fixed realization of the couplings, and the relation betwen the bulk Hilbert spaces of the wormhole and the baby universe Hilbert space.

Speaker: Martin Sasieta

12:20 Lunch & coffee

14 Euclidean folds and deSitter space in Double scaled SYK

We discuss the double scaled limit of the SYK model, and how bulk geometry can emerge from chord diagrams. Particularly we demonstrate that in an appropriate limit the bulk geometry contains deSitter space. This construction sheds light on the thermodynamics of dS space when embedded in a. UV complete microscopic model.

Speaker: Moshe Rozzali

15:00 Coffee

15 Emergent spacetime from fermions: gravitational algebras and Takesaki duality in c=1 strings/matrix quantum mechanics

We briefly review the c=1 string theory and its dual description by a quantum mechanical model of a single N × N Hermitian matrix, i.e. c=1 Matrix Quantum Mechanics (MQM). The ground state of the c=1 MQM admits a Fermi Sea representation, and in the double scaling limit, the perturbative excitations on the Fermi Sea can be studied by a continuum 2D scalar field theory via collective field approach. In the target space picture, this shows the emergence of a 2D spacetime with the tachyon field that lives on it. We study the operator algebra in a subregion of the emergent spacetime away from the potential wall of the MQM, where the string perturbation theory still works, and shows that it gives a type III_1 factor. We then perform the crossed product via the subregion modular operator, which leads to a type II_infinity algebra. Furthermore, by introducing a projection operator on the spectrum of modular operator, the algebra becomes type II_1 factor. On the other hand, We explicitly construct the type II algebra from the canonical anti-communtation relation (CAR) algebra of the fermions in c=1 MQM and shows that the type III_1 factor can be recovered by a dual crossed product suggested by the Takesaki duality.

Speaker: Mengyang Zhang

16:20 Coffee

16 Contributed talk

Speaker: Elisa Tabor

17 Contributed talk

Speaker: Weyne Weng

Thursday 12 November

18 Hamiltonian flows generated by geodesic network lengths in Classical AdS3 gravity

In this work, we study the Hamiltonian flows generated by the individual geodesic lengths in a three-leg geodesic network in classical pure AdS3 gravity. We find that a geodesic length generate both a kink along the corresponding geodesic and a split along the other two geodesics.

Speaker: Jie-qiang Wu

11:00 Coffee

19 New dS Holography from Time-like Entanglement

Speaker: Tadashi Takayanagi

12:20 Lunch & coffee

20 DSSYK matrix model and discrete volume

We can construct a hermitian matrix model whose genus-zero amplitude reproduces the computation of double-scaled SYK model; we call this matrix model the DSSYK matrix model. We argue that the higher genus amplitude of DSSYK matrix model is constructed by gluing the trumpets and the discrete volume of the moduli space of Riemann surfaces. We also comment on the appearance of de Sitter JT gravity as an unstable saddle point of DSSYK matrix model.

Speaker: Kazumi Okuyama

15:00 Coffee

21 Firewalls from the ETH matrix model and sine dilaton gravity

"We study the firewall problem in sine dilaton gravity and its boundary
duals, the double-scaled SYK and ETH matrix models. We compute the
microcanonical probability distribution of the wormhole length in the
Hartle--Hawking state at disk level and with one handle. At late times the
disk distribution localizes on the linearly growing length, while the handle disk gives three channels labelled by the discrete size of the emitted baby universe.
Constraining the moduli with the mapping class group and the
Penington--Witten bound on geodesics, we find finite smooth probabilities
that grow quadratically in time, are equal for the black hole and white
hole channels, and reduce to the JT gravity results of Stanford and Yang.
We also derive the genus-one correction to the wormhole length from its
generating function. On the boundary side, we construct the one-particle
Hilbert space of the ETH matrix model at finite $N$, show that the
two-sided chord basis is overcomplete, and propose Krylov-based complexity
probes of the black hole to white hole transition."

Speaker: Sergio Ernesto Aguilar Gutierrez "

16:20 Coffee

22 Contributed talk

Speaker: Takato Mori

23 Contributed talk

Speaker: Takeshi Morita

Friday 13 November

24 Wormholes and Averaging Over N

Speaker: Jonah Kudler-Flam

11:00 Coffee

25 TBA

Speaker: Keiichiro Furuya

12:20 Lunch & coffee

26 Comments on closed universes in AdS2 and alpha states

Speaker: Mykhaylo Usatyuk