JT gravity and deformed CFTs

A bstract We propose alternative UV completion of pure JT gravity as well as CFT coupled to JT gravity, via a class of deformed 2D CFT. In AdS/CFT with a prescribed classical limit, pure JT gravity in one-sided AdS 2 black hole is argued to be described by certain holographic deformed CFT on a strip. Equivalently, these deformed CFTs can be recast as CFTs on one-sided AdS 2 black hole with emergent conformal boundary condition on a stretched horizon providing a proper UV frame of JT gravity. On the other hand, JT gravity coupled to CFT with fixed central charge of 𝒪(1), is also described by deformed CFT on strip satisfying conformal boundary condition, with a different classical limit. The resulting CFT Hilbert spaces in both of the above classical limits yield the black hole entropy as thermal entropy and the high-energy density of states match that of JT gravity with a precise energy scale correspondence. Moreover, the Hilbert space defined for a two-sided black hole factorizes into two one-sided sectors in both limits. Notably in the second limit, degenerate zero modes of the deformed Hamiltonian characterized by conformal primaries localized at the horizon appear as a residual effect of the stretched horizon boundary condition. Exploiting the second limit, we compute entanglement entropy in one-dimensional quantum systems dual to a conformally glued black hole Poincaré geometry in JT gravity, reproducing a ‘Page curve’ via the quantum extremal surface prescription, with ‘Page time’ set by the stretched horizon cutoff.