Holo-Club: From Volume as a Clock to Boundary Dynamics in JT Gravity

Title: From Volume as a Clock to Boundary Dynamics in JT Gravity

Speaker: Farbod-Sayyed Rassouli (University of Nottingham)

Venue&Time: 11:30 / Blue Room

Abstract:

Different notions of time arise from different choices of observer. In cosmological settings, a particularly natural choice is the spacetime volume, which is conjugate to the cosmological constant. This leads to a notion of unimodular time that deparametrizes the Wheeler–DeWitt equation into a Schrödinger-like evolution equation, while also inducing a natural time variable at the boundary. In this talk, I will first explain how this construction arises in arbitrary dimension, with particular emphasis on the 4D case. I will then turn to Jackiw–Teitelboim gravity, where promoting the vacuum cosmological constant to a dynamical top-form degree of freedom provides a bulk clock in the Henneaux–Teitelboim sense. On the boundary, this modifies the usual Schwarzian dynamics by coupling it to an additional U(1) phase mode, reproducing the universal low-energy structure familiar from complex SYK. I will show how the corresponding boundary theory can itself be rewritten as a (0+1)-dimensional observer action, making explicit the relation between the bulk volume clock and its holographic boundary counterpart.

arXiv:2601.07911