Clocks and Rods in Jackiw-Teitelboim Quantum Gravity

TL;DR

This work develops a boundary-intrinsic radar construction to define diff-invariant bulk points in Jackiw-Teitelboim gravity and computes exact bulk correlators for matter coupled to JT gravity. It demonstrates microcausality of bulk operators and reveals that quantum gravity effects dominate near-horizon and late-time physics, invalidating the semiclassical picture of quantum matter on curved spacetimes. By coupling to CFT matter and employing the Schwarzian action, the authors analyze pure and thermal states, bulk locality, and geometric observables, finding a dramatic breakdown of Rindler geometry at Planckian distances from the horizon. They further explore topologically complete JT gravity, linking late-time correlators to random-matrix theory and showing how nonperturbative effects avert the information paradox in this model. The results highlight the deep role of bulk-frame choices and quantum gravity in near-horizon physics, with universal implications across JT and related holographic setups.

Abstract

We specify bulk coordinates in Jackiw-Teitelboim (JT) gravity using a boundary-intrinsic radar definition. This allows us to study and calculate exactly diff-invariant bulk correlation functions of matter-coupled JT gravity, which are found to satisfy microcausality. We observe that quantum gravity effects dominate near-horizon matter correlation functions. This shows that quantum matter in classical curved spacetime is not a sensible model for near-horizon matter-coupled JT gravity. This is how JT gravity, given our choice of bulk frame, evades an information paradox. This echoes into the quantum expectation value of the near-horizon metric, whose analysis is extended from the disk model to the recently proposed topological completion of JT gravity. Due to quantum effects, at distances of order the Planck length to the horizon, a dramatic breakdown of Rindler geometry is observed.

Figures (23)

• Figure 1: Left: Building the bulk frame from the Poincaré perspective $(T,Z)$. For two reparametrizations (blue and red), we construct the bulk point given two boundary observer time coordinates $t_1$ and $t_2$. The ticks in the clock-ticking pattern are depicted. The bulk location is fuzzy in the Poincaré geometry, but the metric is fixed. Right: Building the bulk frame from the observer's perspective $(t,z)$. The bulk location is fixed, but the metric fluctuates.
• Figure 2: Euclidean bulk-to-bulk two point function \ref{['bulkbulk']} at finite temperature ($\beta=2\pi$, $C=1/2$), with one bulk point at ($t=0,z'=5$) and the second bulk point at ($it,z$), as a function of $z$. Blue: $it=0.1$, Green: $it=0.5$, Orange: $it=1$, Red: $it=\pi$.
• Figure 3: Two scalar operators $\phi$ at $(u,v)$ and $(u',v')$. Singularities in the propagator $\left\langle \phi(u,v) \phi(u',v') \right\rangle$ are encountered on the four lines of lightcone separated events: two direct lines, and two indirect lines obtained by reflection on the holographic boundary.
• Figure 4: Exact (full) and semi-classical (dashed) pure state bulk two-point functions $\left\langle G_{bb}(t,z,z') \right\rangle_M$ and $\bar{G}_M(t,z,z')$ for different values of $M$ ($C=1/2$). Evaluated at $z'=5$ (black vertical line) and for a range of $z$ values. Blue: $it=0.1$. Green: $it=0.5$. Orange: $it=1$. Red: $it=2$.
• Figure 5: Red: Zero-temperature or zero-energy $M=0$ bulk two-point function $G_{bb}^{\infty}$ as a function of $z$ for $z'=1000$, $t=1$ and $C=1/2$. The initial decay close to the lightcone singularity is logarithmic \ref{['pureclaszero']}. Blue: power law (inverse square-root) behavior at $z\gg z'$. Green: power law (linear) behavior at $z\ll z'$.