Quantum Hotspots: Mean Fields, Open EFTs, Nonlocality and Decoherence Near Black Holes

Effective theories describing black hole exteriors resemble open quantum systems inasmuch as many unmeasurable degrees of freedom beyond the horizon interact with those we can see. A solvable Caldeira-Leggett type model a field that mixes unmeasured thermal on shared surface was proposed in arXiv:2106.09854 to provide benchmark against which more complete calculations might be compared. We here use this test two types field-theoretic approximation schemes also lend themselves behaviour: Open EFT techniques (as applied fields themselves, rather than Unruh-DeWitt detectors) and mean-field methods. Mean-field methods are interest because effective Hamiltonians they lead nonlocal; possible source for nonlocality is sometimes entertained being holes near-horizon regime. EFTs compute evolution state, allowing discussion thermalization decoherence even when these occur at such late times perturbative fail often do). Applying both system identifies their domains validity shows how predictions relate garden-variety tools.