Subsystem Entropy in 2d CFT and the Diagonal Approximation

Abstract: Entanglement entropy is a key quantity in quantum many-body physics, yet its computation remains challenging outside of special cases. In this talk, I will present a method based on the diagonal approximation, rooted in the subsystem Eigenstate Thermalization Hypothesis (ETH), for evaluating the entanglement entropy of excited states and thermal ensembles in the large-subsystem limit. Applying this framework to two-dimensional conformal field theories (2D CFTs), we show that it reproduces known results for canonical and microcanonical ensembles and individual primary states, while also yielding new predictions for KdV generalized Gibbs ensembles. Our approach resolves tensions between explicit CFT computations and ETH expectations, providing indirect support for the generalized ETH in 2D CFTs.

condensed mattergeneral relativity and quantum cosmologyHEP - latticeHEP - theorymathematical physicsquantum physics

Audience: researchers in the topic

Quantum Theories of Fields, Matter, and Strings

Series comments: A series of talks covering a broad range of topics in theoretical physics, including high energy theory, condensed matter, and string theory.

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