Modular Hamiltonians, relative entropy, and the entropy-area law in de Sitter spacetime
Date: 08 APRIL 2026 from 15:00 to 16:00
Event location: IR-2A
In a very general setting, entropy quantifies the amount of information about a system that an observer has access to. However, in contrast to quantum mechanics, in quantum field theory naive measures of entropy are divergent. To obtain finite results, one needs to consider measures such as relative entropy, which can be computed from the modular Hamiltonian using Tomita-Takesaki theory.
In this talk, I will present a modular Hamiltonian that was recently derived for conformal fields in diamond regions of conformally flat spacetimes (including de Sitter). I will give results for the relative entropy between the de Sitter vacuum state and a coherent excitation thereof in diamonds and wedges, and show explicitly that the result satisfies the expected properties for a relative entropy. Finally, I will use thermodynamic relations to determine the local temperature that is measured by an observer, and consider the backreaction of the coherent excitation on the geometry to prove an entropy-area law for de Sitter spacetime.
Based on arXiv:2308.14797, 2310.12185 and 2311.13990.