Quantum width of spherically symmetric black hole horizons is defined by signal escape timing and calculated in perturbative quantum gravity to often greatly exceed the Planck length, scaling as sqrt(l_P r_s^2 / sigma_perp) for Schwarzschild patches.
Effective density matrix for vacua in asymptotically flat gravity
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abstract
We explicitly construct the density matrix associated to the vacuum state of a large spherically symmetric causal diamond of area $A$ in four-dimensional asymptotically flat gravity. We achieve this using the soft effective action, which characterizes the low-energy gravitational degrees of freedom that arise in the long-distance limit of the Einstein-Hilbert action and consists of both the soft graviton mode and the Goldstone mode arising from the spontaneous breaking of supertranslation symmetry. Integrating out the soft graviton mode, we obtain an effective action for purely the Goldstone mode, from which we extract the density matrix and therefore the modular Hamiltonian $K_s$ associated to the vacuum state. As a corollary, we explicitly compute the mean and variance of $K_s$, finding $\langle \Delta {K}_s^2 \rangle = A/\epsilon_{\text{UV}}^2$, with $\epsilon_{\text{UV}}$ being a length-scale UV cutoff on the celestial sphere.
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hep-th 3representative citing papers
Phase space of arbitrary null cut in Minkowski spacetime is symplectomorphic to infrared phase space of asymptotically flat gravity, mapping cut fluctuations to leading soft graviton mode and supertranslation Goldstone mode to cut size times null time offset.
The angle-averaged soft and Goldstone modes of 4D asymptotically flat gravity are symplectically identified with the radial-size and area-edge modes of a spherically symmetric Minkowski causal diamond.
citing papers explorer
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Quantum Fluctuations of the Black Hole Horizon
Quantum width of spherically symmetric black hole horizons is defined by signal escape timing and calculated in perturbative quantum gravity to often greatly exceed the Planck length, scaling as sqrt(l_P r_s^2 / sigma_perp) for Schwarzschild patches.
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Mapping the Infrared Phase Space of Gravity to Finite Subregions
Phase space of arbitrary null cut in Minkowski spacetime is symplectomorphic to infrared phase space of asymptotically flat gravity, mapping cut fluctuations to leading soft graviton mode and supertranslation Goldstone mode to cut size times null time offset.
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From Asymptotically Flat Gravity to Finite Causal Diamonds
The angle-averaged soft and Goldstone modes of 4D asymptotically flat gravity are symplectically identified with the radial-size and area-edge modes of a spherically symmetric Minkowski causal diamond.