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arXiv · 2508.14512

Necessary and sufficient conditions for correctness of complex Langevin

Michael Mandl·Erhard Seiler·Dénes Sexty
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Abstract

We derive a family of correctness conditions for complex Langevin simulations. In particular, we show that if in a given theory the expectation values of all observables within a particular space satisfy the theory's Schwinger-Dyson equations as well as certain bounds, then these expectation values are necessarily correct. In fact, these findings are not only valid in the context of complex Langevin simulations, but they also hold for general probability densities on complex manifolds, given an initial complex density on a real manifold. We stress that, while the proposed conditions are necessary and sufficient in a mathematical sense, their practical use is not to prove the correctness of obtained simulation results. Rather, they are mainly useful for detecting incorrect convergence. In particular, we test these criteria in a few simple one- and two-dimensional toy models and find that they are indeed capable of ruling out incorrect results without the need of exact solutions.

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Michael Mandl, Erhard Seiler, Dénes Sexty. 2025-08-20. Necessary and sufficient conditions for correctness of complex Langevin. https://doi.org/10.1088/1751-8121%2Fae2245

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