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An intuitive construction of modular flow

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arxiv 2309.16766 v2 pith:FEQB66OT submitted 2023-09-28 hep-th math-phmath.MPquant-ph

An intuitive construction of modular flow

classification hep-th math-phmath.MPquant-ph
keywords modularflowfundamentaloperatortheoryanalysisconstructioncontribution
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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The theory of modular flow has proved extremely useful for applying thermodynamic reasoning to out-of-equilibrium states in quantum field theory. However, the standard proofs of the fundamental theorems of modular flow use machinery from Fourier analysis on Banach spaces, and as such are not especially transparent to an audience of physicists. In this article, I present a construction of modular flow that differs from existing treatments. The main pedagogical contribution is that I start with thermal physics via the KMS condition, and derive the modular operator as the only operator that could generate a thermal time-evolution map, rather than starting with the modular operator as the fundamental object of the theory. The main technical contribution is a new proof of the fundamental theorem stating that modular flow is a symmetry. The new proof circumvents the delicate issues of Fourier analysis that appear in previous treatments, but is still mathematically rigorous.

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Cited by 4 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Uniqueness of null-local modular flow

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    For the free massless scalar in a Minkowski causal diamond, the vacuum is the unique state or weight in the vacuum sector whose modular flow is local on the null boundary.

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  3. Excitability in quantum field theory

    hep-th 2026-04 unverdicted novelty 6.0

    For zero-mean Gaussian states in generalized free field theories, one-way local excitability always implies two-way excitability, generalizing the quasiequivalence theorems of Powers, Stormer, van Daele, Araki, and Yamagami.

  4. Fiducial observers and the thermal atmosphere in the black hole quantum throat

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    A semiclassical construction of fiducial observers in JT gravity, fixed by conformal isometry flow, is extended to the quantum regime to compute wormhole contributions yielding finite thermal entropy and a quantum des...