Path integral contour deformations for observables in $SU(N)$ gauge theory

29 Jan 2021  ·  William Detmold, Gurtej Kanwar, Henry Lamm, Michael L. Wagman, Neill C. Warrington ·

Path integral contour deformations have been shown to mitigate sign and signal-to-noise problems associated with phase fluctuations in lattice field theories. We define a family of contour deformations applicable to $SU(N)$ lattice gauge theory that can reduce sign and signal-to-noise problems associated with complex actions and complex observables. For observables, these contours can be used to define deformed observables with identical expectation value but different variance. As a proof-of-principle, we apply machine learning techniques to optimize the deformed observables associated with Wilson loops in two dimensional $SU(2)$ and $SU(3)$ gauge theory. We study loops consisting of up to 64 plaquettes and achieve variance reduction of up to 4 orders of magnitude.

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High Energy Physics - Lattice Statistical Mechanics Nuclear Theory