$T^2$ deformations in the double-scaled SYK model: Stretched horizon thermodynamics

Abstract: It has been recently realized that the bulk dual of the double-scaled SYK (DSSYK) model has both positive and negative Ricci curvature and is described by a dilaton-gravity theory with a $\sin(\Phi)$ potential arXiv:2404.03535. We study T$^2$-deformations in the DSSYK model after performing the ensemble averaging to probe regions of positive and approximately constant curvature. The dual finite cutoff interpretation of the deformation allows us to place the DSSYK model in the stretched horizon of the bulk geometry, partially realizing a conjecture of Susskind arXix:2109.14104. We show that the energy spectrum and thermodynamic entropy are well-defined for a contour reaching these regions. Importantly, the system displays a phase transition from a thermodynamically stable to an unstable configuration by varying its microcanonical temperature; unless it is located on any of the stretched horizons, which is always unstable. The thermodynamic properties in this model display an enhanced growth as the system approaches the stretched horizon, and it scrambles information at a (hyper)-fast rate.