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Algebras and States in JT Gravity

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We analyze the algebra of boundary observables in canonically quantised JT gravity with or without matter. In the absence of matter, this algebra is commutative, generated by the ADM Hamiltonian. After coupling to a bulk quantum field theory, it becomes a highly noncommutative algebra of Type II$_\infty$ with a trivial center. As a result, density matrices and entropies on the boundary algebra are uniquely defined up to, respectively, a rescaling or shift. We show that this algebraic definition of entropy agrees with the usual replica trick definition computed using Euclidean path integrals. Unlike in previous arguments that focused on $\mathcal{O}(1)$ fluctuations to a black hole of specified mass, this Type II$_\infty$ algebra describes states at all temperatures or energies. We also consider the role of spacetime wormholes. One can try to define operators associated with wormholes that commute with the boundary algebra, but this fails in an instructive way. In a regulated version of the theory, wormholes and topology change can be incorporated perturbatively. The bulk Hilbert space $\mathcal{H}_\mathrm{bulk}$ that includes baby universe states is then much bigger than the space of states $\mathcal{H}_\mathrm{bdry}$ accessible to a boundary observer. However, to a boundary observer, every pure or mixed state on $\mathcal{H}_\mathrm{bulk}$ is equivalent to some pure state in $\mathcal{H}_\mathrm{bdry}$.

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Smooth horizons from topology change in canonical quantum gravity

hep-th · 2026-06-04 · unverdicted · novelty 7.0

Topology change in canonical JT gravity resolves the firewall paradox by making the connected two-interior branch dominate after Page time, with gravitational constraints annihilating the firewall branch and identifying horizon vacuum and early radiation purity as the same Dirac observable.

The mini-Page Curve in Cosmology

hep-th · 2026-07-09 · conditional · novelty 6.5

In 2D centaur geometries the entropy difference of a modular-conjugate Hawking-pair probe traces an inverse mini-Page curve that bottoms at τ≈β/8, marking when information begins to leave the cosmological horizon.

Single-Sided Black Holes in Double-Scaled SYK Model and No Man's Island

hep-th · 2025-11-03 · unverdicted · novelty 6.0

In the double-scaled SYK model with an end-of-the-world brane, the boundary algebra for a single-sided black hole is a type II1 von Neumann factor with non-trivial commutant, preventing full bulk reconstruction and creating a no man's island behind the horizon.

Toward Krylov-based holography in double-scaled SYK

hep-th · 2025-10-26 · unverdicted · novelty 6.0

Establishes a threefold duality linking Krylov complexity growth rate to wormhole velocity and proper momentum in DSSYK holography, with higher moments capturing replica wormholes and Krylov entropy equaling parent-geometry von Neumann entropy after tracing baby universes.

Algebraic traversable wormholes

hep-th · 2025-08-18 · unverdicted · novelty 6.0

Proposes a new large N limit dual to back-reacted traversable wormholes via algebra-at-infinity operators and algebraically reproduces the Maldacena-Stanford-Yang result on left-right observer effects.

Timelike entanglement entropy Revisited

hep-th · 2025-03-25 · unverdicted · novelty 5.0

An operator-algebraic definition of timelike entanglement entropy in QFT is shown to be real-valued via the timelike tube theorem.

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