Modular theory and affine representations on the Rindler horizon

Abstract:We develop a group-theoretic interpretation of the Unruh effect based on affine symmetry on a light ray and relate it to modular theory. For a massless scalar field in two spacetime dimensions inertial and uniformly accelerated observers select two different flows within the same chiral one-particle structure, respectively, null translations and dilations. Minkowski modes are adapted to translations, while Rindler modes are adapted to dilations, with the Mellin transform providing the natural bridge between them. When a Minkowski positive-frequency mode is restricted to a single Rindler wedge, its comparison with Rindler modes is non-unitary within the positive-frequency sector. Modular theory gives the corresponding operator-algebraic interpretation: on the horizon the modular flow of the half-line algebra is implemented by dilations, and the restricted vacuum satisfies the KMS condition. The affine group thus appears as the minimal symmetry structure underlying thermality on the Rindler horizon.

19 pages, 2 figures. Invited contribution to the special issue "Quantum Horizons: Emerging Interfaces of Quantum Mechanics, Quantum Information, and Gravitation" of Fortschritte der Physik. Matches published version

arXiv:2606.01071 [hep-th]

(or arXiv:2606.01071v2 [hep-th] for this version)

Fortschritte der Physik 74, no. 9 (2026): e70150

https://doi.org/10.1002/prop.70150 DOI(s) linking to related resources