Deforming the Double-Scaled SYK & Reaching the Stretched Horizon From Finite Cutoff Holography

Abstract: We study the properties of the double-scaled SYK (DSSYK) model under chord Hamiltonian deformations based on finite cutoff holography for general dilaton gravity theories with Dirichlet boundaries. The formalism immediately incorporates a lower-dimensional analog of $\text{T}\bar{\text{T}}(+Λ_2)$ deformations, denoted $T^2(+Λ_1)$, as special cases. In general, the deformation mixes the chord basis of the Hilbert space in the seed theory, which we order through a modification of the Lanczos algorithm. The resulting chord number in the ordered basis represents a wormhole length at a finite cutoff in the bulk. We study the thermodynamic properties of the deformed theory; the evolution of $n$-point correlation functions with matter chords; the growth of complexity of the Hartle-Hawking state; and the entanglement entropy between the double-scaled algebras for a given chord state. The latter, in the triple-scaling limit, manifests as the minimal codimension-two area in the bulk following the Ryu-Takayanagi formula. By performing a sequence of $T^2$ and $T^2+Λ_1$ deformations in the upper tail of the energy spectrum in the deformed DSSYK, we concretely realize the cosmological stretched horizon proposal in de Sitter holography by Susskind. We discuss other extensions with sine dilaton gravity, end-of-the-world branes, and the Almheiri-Goel-Hu model.