dorsal/arxiv
View SchemaUnimodular time in JT gravity: a holographic clock
| Authors | Altay Etkin, Farbod-Sayyed Rassouli |
|---|---|
| Categories | |
| ArXiv ID | 2601.07911vv1 |
| URL | https://arxiv.org/abs/2601.07911 |
| License | http://creativecommons.org/licenses/by-nc-nd/4.0/ |
Abstract
How is a ''bulk clock'' encoded holographically? We address this in Jackiw-Teitelboim (JT) gravity, where a natural physical clock emerges by promoting the vacuum energy to a dynamical variable: the vacuum cosmological constant becomes a top form degree of freedom conjugate to spacetime volume, thereby defining a notion of bulk physical time. This construction is naturally formulated in the Henneaux-Teitelboim (HT) framework. We show that the boundary dynamics is the Schwarzian mode coupled to a free particle on $U(1)$, matching the universal low-energy effective action of the complex SYK model. By further clarifying the role of the vacuum cosmological constant as a top form, we establish the equivalence between JT gravity coupled to two-dimensional Maxwell theory and 2d HT gravity via an explicit field redefinition. The initial question is addressed: we show that the resulting boundary theory can itself be rewritten as an observer action, equivalently a $(0+1)$-dimensional HT theory. This yields a direct identification of the boundary clock with the $U(1)$ phase mode, and makes its relation to the bulk clock explicit.
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"abstract": "How is a \u0027\u0027bulk clock\u0027\u0027 encoded holographically? We address this in Jackiw-Teitelboim (JT) gravity, where a natural physical clock emerges by promoting the vacuum energy to a dynamical variable: the vacuum cosmological constant becomes a top form degree of freedom conjugate to spacetime volume, thereby defining a notion of bulk physical time. This construction is naturally formulated in the Henneaux-Teitelboim (HT) framework. We show that the boundary dynamics is the Schwarzian mode coupled to a free particle on $U(1)$, matching the universal low-energy effective action of the complex SYK model. By further clarifying the role of the vacuum cosmological constant as a top form, we establish the equivalence between JT gravity coupled to two-dimensional Maxwell theory and 2d HT gravity via an explicit field redefinition. The initial question is addressed: we show that the resulting boundary theory can itself be rewritten as an observer action, equivalently a $(0+1)$-dimensional HT theory. This yields a direct identification of the boundary clock with the $U(1)$ phase mode, and makes its relation to the bulk clock explicit.",
"arxiv_id": "2601.07911",
"authors": [
"Altay Etkin",
"Farbod-Sayyed Rassouli"
],
"categories": [
"hep-th",
"gr-qc"
],
"license": "http://creativecommons.org/licenses/by-nc-nd/4.0/",
"title": "Unimodular time in JT gravity: a holographic clock",
"url": "https://arxiv.org/abs/2601.07911",
"version": "v1"
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