Quantum Gravity in a Universe Without an Outside

• Yasunori Nomura

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

Relational path integral and quantum frame covariance in gravity

• Philipp Hoehn

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12) 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.]

INTEGRABILITY-CHAOS TRANSITION OF THE ADS3 TENSIONLESS STRINGS

• Cheng Peng

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

Contributed talk

• Ahmed Abdalla

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

Contributed talk

• Kotaro Tamaoka

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

Contributed talk

• Javier Moreno

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

Contributed talk

• Joydeep Naskar

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

Matrix model duals of JT gravity multiverses

• Ping Gao

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

TBA

• Zhenbin Yang

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

TBA

• Jan Boruch

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

Codimension-Zero Holographic Complexity and Spectral Three-Point Correlators

• Shanming Ruan

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12) 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.

Runaways in the no-boundary wavefunction

• Kristan Jensen

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

An SYK wormhole under the microscope

• Martin Sasieta

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12) 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.

Euclidean folds and deSitter space in Double scaled SYK

• Moshe Rozzali

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12) 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.

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

• Mengyang Zhang

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12) 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.

Contributed talk

• Elisa Tabor

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

Contributed talk

• Weyne Weng

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

Hamiltonian flows generated by geodesic network lengths in Classical AdS3 gravity

• Jie-qiang Wu

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12) 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.

New dS Holography from Time-like Entanglement

• Tadashi Takayanagi

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

DSSYK matrix model and discrete volume

• Kazumi Okuyama

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12) 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.

Firewalls from the ETH matrix model and sine dilaton gravity

• Sergio Ernesto Aguilar Gutierrez "

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12) "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."

Contributed talk

• Takato Mori

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

Contributed talk

• Takeshi Morita

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

Wormholes and Averaging Over N

• Jonah Kudler-Flam

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

TBA

• Keiichiro Furuya

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)

Comments on closed universes in AdS2 and alpha states

• Mykhaylo Usatyuk

Room: Okoichi Hall (except for Nov 12) & Suzuki Umetaro Hall (Nov 12)