Complex Langevin kernels for real-time SU(N) lattice gauge theory in 3+1 dimensions

Abstract

We investigate complex Langevin (CL) dynamics for real-time SU($N$) gauge theories in 3+1 dimensions and introduce new kernel modifications tailored for lattice gauge theory (LGT). Using the anisotropic kernel as a baseline, we demonstrate that on a rectangular regularized Schwinger-Keldysh time contour, stable simulations are possible for pure SU(2) gauge theory up to a real-time extent of $2\beta$ at a bare coupling $g=0.5$, where $\beta$ denotes the inverse temperature. We show that a contour-dependent phase kernel extends this reach to $3\beta$, while a local, field-dependent kernel based on traced plaquettes achieves $3.5\beta$. These constructions represent the first application of such kernels to LGTs, especially in 3+1 dimensions. To validate the approach, we generalize the CL correctness criterion based on the drift magnitude to kernelled dynamics, providing a practical tool to assess correct convergence. Our results substantially advance the applicability of CL to real-time simulations in Minkowski space, establishing a framework for controlled studies of non-Abelian gauge theories at unprecedented time scales. A forthcoming paper applies these developments to the computation of unequal-time correlation functions.

arXiv comment23 pages, 5 figures, 2 tables